Baseline Population Monitoring of Key Seabird Species 2006-2007
Macquarie Island Marine Park
Final Report for the Department of the Environment and Water Resources
June 2007
Parks and Wildlife Service Department of Tourism, Arts and the Environment Tasmania
Biodiversity Conservation Branch Department of Primary Industries and Water Tasmania
88ii Executive Summary This program aims to investigate the breeding activity of a number of key threatened seabirds on Macquarie Island. Long term monitoring of these species is necessary to follow trends in their population dynamics, and their subsequent response to the eradication of feral pest species. Funding from the federal Department of the Environment and Water Resources, for the Baseline Population Monitoring of Key Seabird Species on Macquarie Island Project, has enabled this to occur.
Little information is available about the burrow-nesting seabirds breeding on Macquarie Island prior to the 1890s. Collection and records from then to 1914 indicate that some species that are now rarely seen were still relatively common on the main island. By this time feral cats had been on the island for at least 60 years; and wekas, rabbits and rodents were established and beginning to have impacts.
Surveys carried out in the 1970s and 1980s established baseline data for several petrel species. Following eradication of feral cats in 2000, grey petrels re-established breeding sites on the Island and numbers of some other species started to increase. Unfortunately, as the benefits from the removal of cats began to be felt, habitat destruction due to rabbit grazing has become a serious issue for most burrow-nesting species. Habitat destruction by introduced species was identified in 2005 as one of the main threats to Macquarie Island’s seabirds (see http://www.deh.gov.au/biodiversity/threatened/publications/recovery/seabirds/index.html), and this year’s results have confirmed that this threat continues.
Another species whose status is unknown on Macquarie Island is the Rockhopper penguin. Populations of this species have declined markedly at some other breeding sites since the 1940s and this has caused concerns about their status worldwide.
This report documents results from the program for the period between April 2006 and May 2007. It compliments data collected since the successful conclusion of the cat eradication program. This season’s program focused on Grey, White-headed, Soft-plumaged and Blue Petrels, Sooty Sheawaters and Rockhopper Penguins, as well as documenting some rarer species. Each species is discussed separately including details on monitoring objectives, methods used, results and recommendations for future work.
Grey Petrels (Procellaria cinerea) Coinciding with the final stages of a successful cat eradiation program, Grey Petrels were found breeding again on Macquarie Island in 1999/00. Since this discovery, winter breeding activity has been monitored each year to the present time. Numbers rapidly increased over subsequent years to reach a conservative estimate of 70 pairs during the 2005 breeding season. Grey Petrel activity has been recorded at twenty-eight locations around the Island. The monthly monitoring program to document breeding activity at the main sites around the island was continued this season, and some less intensive monitoring was conducted at other small and remote breeding colonies.
In 2006 153 burrows were investigated for signs of Grey Petrel activity at the monthly monitored sites (these include the vast majority of known breeding burrows). 67 breeding attempts were confirmed, but only 15 chicks fledged at the end of the season. Breeding success at these sites was calculated to be 22%, which was less then half of that recorded during the previous season. All these successful breeding attempts were on North Head. Only eight of the other twelve known breeding colonies around the Island were visited this season due site instability. Grey Petrel activity was recorded at four of these sites, but only one chick was thought to have fledged.
The proportion of nest failures was much higher in 2006 then the past seven years since monitoring began. Physical deterioration of many of the Grey Petrel breeding colonies was ii thought to be a major influence on breeding success. Virtually all colonies had prominent signs of rabbit damage, and most have significantly deteriorated over the last four years.
White-headed Petrels (Pterodroma lessonii) Four White-headed Petrel sites were monitored for breeding success as part of the 2006/7 work program. Two existing sites located at the southern end of the island, and two new sites, in the north, were established and monitored this season. One hundred and thirty-five marked burrows across the sites were investigated for signs of breeding activity. Sixty-four chicks fledged, with only twenty nest failures recorded. This suggests an overall increase in breeding success this season.
Thirty seven White-headed Petrel carcasses, resulting from skua attacks, were found in the vicinity of the sites over the season. The number of carcasses was less than that recorded last season. Rat activity was not noted on any of the sites. Damage from rabbit activity was very obvious at some sites. Extensive grazing and tunnelling continues to cause erosion, increasing burrow exposure to prevailing weather conditions and the incidence of burrow collapse. These impacts have increased the vulnerability of this species to predation from skuas, and it is probable that birds are also being directly affected by rabbits using their burrows.
Sooty Shearwaters (Puffinus griseus) Three of the many Sooty Shearwater breeding sites around the Island were established and monitored this season. One hundred and thirty-seven burrows were investigated for signs of breeding activity. Thirty-two chicks fledged from forty eight confirmed breeding burrows. Monitoring breeding success in this species was difficult due to complex burrows.
Seven sites, containing approximately 152 active burrows were located between Cape Toutcher and Aurora Point when completing the whole island census of breeding colonies started in 2005/6. Results from this current census and a previous one conducted in the early 1980’s were compared with inconclusive results. Site quality at most Sooty Shearwater sites around the Island was noted to be very poor with extensive rabbit damage being noted on nearly all sites. For this reason, rabbit activity is likely to be having a major impact on Sooty Shearwaters.
Blue Petrels (Halobaena caerulea) Of all the burrowing petrel species monitored on the Island this season, Blue Petrels appear to have been affected the most by habitat modification and predation. Breeding activity was only observed on four of the twelve mainland sites investigated this season and only four chicks were thought to have fledged. Although this year’s results show more breeding attempts when compared to last season, it is still well below the levels noted in the years immediately following cat eradication and subsequent local rat baiting.
A combination of factors are thought to be causing the current low breeding. Many sites have been heavily grazed by rabbits which has resulted in extensive changes in the vegetation that previously protected burrows. Skuas are preying heavily on adult birds throughout the season with numerous carcasses being found in their territories. Evidence of rat activity correlated with failed burrows suggests that rats are also impacting on nesting birds.
Soft-plumaged Petrel (Pterodroma mollis) Soft-plumaged petrels have long been suspected of breeding on Macquarie Island, but this was first confirmed this season when an adult bird was found incubating an egg in a burrow near Waterfall Bay. Two chicks and egg remains were subsequently discovered at this site, but chick fledging was not verified. Birds were also heard calling and observed at night in a number of areas early in the season, but no additional burrows were located in subsequent searches. One pair of birds was found prospecting in a burrow on the tip of North Head near the end of the season.
ii The Soft-plumaged petrel population breeding on the Island is thought to be small. Skuas prey on this species as is evidenced by the collection of wing sets from their territories and around the Island during the year. The rapid decline of tussock vegetation on Macquarie Island due to rabbit grazing is highly likely to detrimentally impact on Soft-plumaged Petrel breeding sites. Rabbits were observed in Soft-plumaged Petrel breeding burrows, and it is likely that rabbit activity in the burrows is having a negative impact on this small species of petrel. Rats are known to prey on this species on other Islands but their impacts here are unknown.
Other Petrel Species Despite searching all known and suspected breeding sites, no sign of any breeding activity was found for Cape Petrels (Daption capense), Fairy Prion (southern) (Pachyptila tutur subantarctica) and Diving Petrel species (Pelecanoides sp) this season. A combination of breeding site modification, rabbit grazing, rat predation, and skua predation are thought to have contributed to a decline of breeding activity of these species on Macquarie Island, but this does not exclude their breeding in some remote locations, particularly off-shore stacks. All opportunistic observations of these species were recorded during the season. Skua kills of the far more populous Antarctic Prion (Pachyptila desolata) were also recorded.
Rockhopper Penguins (Eudyptes chrysocome) Little is known about the status of the Rockhopper Penguin population on Macquarie Island. This species has suffered dramatic declines at a number of other breeding locations across their range. Over this season the majority (46) of breeding colonies around the Island were mapped for the first time and a number of long term monitoring options were trialled. These included nest counts in some smaller colonies, establishment of photomonitoring points and colony perimeter mapping – recommendations are made on suitable methods for each colony. Some chick counts were also undertaken to determine breeding success at smaller colonies. A combination of options at a number of colonies is thought to be the most effective way of detecting change in the overall population.
iii Table of Contents
Executive Summary ...... ii 1. Introduction ...... 1 Acknowledgements ...... 1 2. Grey Petrel (Procellaria cinerea) ...... 2 2.1 Objectives of the 2006 season ...... 2 2.2 Background ...... 2 2.3 Methods ...... 4 2.3.1 Status of sites at the beginning of the 2006 season .. .. 4 2.3.2 Monthly Monitoring ...... 4 2.3.3 Monitoring methods ...... 4 2.3.4 Other locations around the Island ...... 6 2.3.5 Site and burrow numbering/marking ...... 6 2.3.6 Burrow descriptions ...... 6 2.3.7 Rabbit Grazing Damage Monitoring ...... 6 2.3.8 Photomonitoring ...... 7 2.3.9 Search for new breeding colonies ...... 7 2.3.10 Collection of eggs and carcasses ...... 7 2.3.11 Monitoring of feral species, predators and other burrowing seabirds on sites ...... 7 2.3.12 Update Macquarie Island Burrowing Petrel Database .. .. 7 2.4 Results ...... 8 2.4.1 Monthly Monitoring ...... 8 2.4.2 Results from other colonies ...... 9 2.4.3 Burrow descriptions ...... 10 2.4.4 Damage to sites and burrows ...... 11 2.4.5 Egg measurements ...... 11 2.4.6 New breeding burrows and locations ...... 11 2.4.7 Rat Rabbit and Skua Activity ...... 12 2.4.8 Sympatric species ...... 13 2.5 Discussion ...... 13 2.6 Recommendations ...... 18 2.6.1 Summary of biological information and monitoring suggestions .. 19 3. White-headed Petrel (Pterodroma lessoni) ...... 20 3.1 Objectives of the 2006 season ...... 20 3.2 Background ...... 20 3.2 Methods ...... 21 3.3 Results ...... 23 3.4 Discussion ...... 27 3.5 Recommendations ...... 28 3.5.1 Summary of biological information and monitoring suggestions 29 4. Sooty Shearwater (Puffinus griseus) ...... 30 4.1 Objectives of the 2006 season ...... 30 4.2 Background ...... 30 4.3 Methods ...... 31 4.3.1 Monitoring at Breeding Colonies ...... 31 4.3.2 Census for Breeding Colonies ...... 32 4.4 Results ...... 33 4.4.1 Sooty Shearwater Site Monitoring ...... 33 4.4.2 Census for breeding Colonies ...... 35 4.5 Discussion ...... 36 4.6 Recommendations ...... 39 4.6.1 Summary of biological information and monitoring suggestions 40 5. Blue Petrels (Halobaleana caerulea) ...... 41 5.1 Objectives of the 2006 season ...... 41 5.2 Background ...... 41 5.3 Methods ...... 42 1
5.4 Results ...... 43 5.5 Discussion ...... 45 5.6 Recommendations ...... 48 5.6.1 Summary of biological information and monitoring suggestions 49 6. Soft-plumaged Petrel (Pterodroma mollis) ...... 50 6.1 Objectives of the 2006 season ...... 50 6.2 Background ...... 50 6.3 Methods ...... 52 6.3.2 Monitoring of active burrows ...... 52 6.3.1 Searching for Activity ...... 52 6.4 Results ...... 54 6.5 Discussion ...... 56 6.6 Recommendations ...... 56 6.6.1 Summary of biological information and monitoring suggestions 57 7. Cape Petrel (Daption capense), Antarctic Prion (Pachyptila desolata), Fairy Prion (southern) (Pachyptila tutur subantarctica) and Diving Petrel sp (Pelecanoides sp) ...... 58 7.1 Objectives of the 2006 season ...... 58 7.2 Background ...... 58 7.2.1 Cape Petrel ...... 58 7.2.2 Antarctic Prion ...... 59 7.2.3 Fairy Prion (southern) ...... 59 7.2.4 Diving Petrels ...... 56 7.3 Methods ...... 61 7.3.1 Cape Petrel ...... 61 7.3.2 Antarctic Prion ...... 61 7.3.3 Fairy Prion ...... 61 7.3.4 Diving Petrels ...... 61 7.4 Results ...... 61 7.5 Discussion ...... 63 7.6 Recommendations ...... 64 8. Rockhopper Penguin (Eudyptes chrysocome) Monitoring .. .. 65 8.1 Objectives of the 2006 season ...... 65 8.2 Background ...... 65 8.3 Methods ...... 67 8.3.1 Monitoring ...... 68 8.3.1.1 Detecting change through population estimates .. 68 8.3.1.2 Detecting change through photomonitoring points .. 69 8.3.1.3 Detecting change through colony mapping .. .. 69 8.3.1.4 Breeding success ...... 70 8.4 Results ...... 70 8.5 Discussion ...... 75 8.5.1 Colony location mapping ...... 75 8.5.2 Total nest counts ...... 76 8.5.3 Population estimate ...... 76 8.5.4 Photomonitoring ...... 77 8.5.4 Colony Perimeter Mapping ...... 78 8.5.5 Perimeter observations ...... 78 8.5.6 Breeding Success ...... 78 8.6 Recommendations ...... 79 9. References ...... 81
2 Figures Figure 2.1 Location of currently known past and present Grey Petrel breeding sites on Macquarie Island and areas of prospecting activity in the 2006 season .. 3 Figure 2.2 Grey Petrel breeding sites monitored each month during the 2006 season .. 5 Figure 2.3 Location of New Grey Petrel activity on North Head...... 12 Figure 2.4 Graph comparing Grey Petrel Breeding Success since the 2000 season .. 14 Figure 2.5 Photomonitoring at some Grey Petrel sites since 2003 ...... 16 Figure 3.1 Location of White-headed Petrel sites monitored during the 2006/7 season 22 Figure 4.1 Areas of Sooty Shearwater Activity around Macquarie Island .. .. 34 Figure 5.1 Blue Petrel activity on Macquarie Island ...... 45 Figure 6.1 Approximate locations where Soft-plumaged Petrels have been heard and unconfirmed breeding burrow locations 2000 to 2003...... 51 Figure 6.2 Soft-plumaged Petrel Observation Records for the 2006/7 Season .. .. 54 Figure 8.1 Approximate location of Rockhopper penguin colonies around Macquarie Island – Northern 1/3 ...... 72 Figure 8.2 Approximate location of Rockhopper penguin colonies around Macquarie Island – Central 1/3 ...... 73 Figure 8.3 Approximate location of Rockhopper penguin colonies around Macquarie Island – Southern 1/3 ...... 74
Tables Table 2.1 Summary of results from monthly monitoring of Grey Petrel Burrows during the 2006 season ...... 8 Table 2.2 2006 Results from one off visit to other known Grey Petrel sites around the Island ...... 10 Table 2.3 Measurements of abandoned Grey Petrel eggs collected during the 2005/6 breeding seasons ...... 11 Table 2.4 Comparison of results from the 2005 and 2006 breeding season .. .. 13 Table 2.5 Comparison of 2005 and 2006 breeding success results and Rabbit Grazing Damage at Grey Petrel sites on Macquarie Island ...... 17 Table 3.1 Summary of results from monthly monitoring of White-headed Petrel burrows over the 2006 season ...... 24 Table 3.2 Measurements of abandoned White-headed Petrel eggs collected during the 2006/7 breeding seasons ...... 26 Table 3.3 Measurements taken from White-headed Petrel Carcasses over the 2006-7 breeding season ...... 27 Table 3.4 Comparison of White-headed Petrel breeding activity results from 2005/6 and 2006/7 seasons ...... 27 Table 4.1 Summary of results from monthly monitoring of Sooty Shearwater burrows over the 2006/7 season ...... 33 Table 4.2 Breeding colonies found during 2006/7 Sooty Shearwater census .. .. 35 Table 4.3 Measurements of abandoned Sooty Shearwater eggs collected during the 2006/7 breeding seasons ...... 35 Table 4.4 Measurements taken from Sooty Shearwater wing sets over the 2006-7 breeding season ...... 36 Table 4.5 Comparison of Sooty Shearwater Census results from Brothers (1984) and 2005/7 ...... 37 Table 5.1 Results from breeding activity monitoring conducted at Macquarie Island Blue Petrel colonies during the 2005/6 and 2006/7 seasons ...... 44 Table 5.2 Measurements taken from Blue Petrel wing sets over the 2006-7 breeding Season ...... 44 Table 6.1 Wing measurements taken from Soft-plumaged Petrel remains found during the 2006-7 breeding season ...... 55 Table 7.1 Observations of Cape Petrels, Diving Petrel sp and Fairy Prions over the 2006/7 season ...... 62 Table 7.2 Wing measurements taken from Antarctic Prion remains found during the 2006-7 breeding season ...... 63 Table 8.1 Breeding success at ten small Rockhopper Penguin Colonies over the 2006/7 season ...... 71 3 1. Introduction
The population status of seabirds on Macquarie Island is dynamic as the populations have been differentially affected by as range of threats – most notably interactions with fishing operations and impacts by feral pests. One of the strategic objectives of the Macquarie Island Marine Park is to protect the conservation values of the south east portion of the Macquarie Island region including the migratory, feeding and breeding ranges of marine birds and mammals, including threatened species.
Unfortunately, the population size and status of many species of Macquarie Island threatened seabirds remains unknown. Burrowing petrel species have been adversely affected by predation by cats and rats and habitat loss as a result of rabbit grazing. Another species whose status is unknown on Macquarie Island is the Rockhopper penguin. This species has declined by 90% since the 1940s at other breeding locations such as Falkland and Campbell Islands so there is interest in their status at other locations.
Since early 2005 collaborative funding by State and Australian Federal Government has funded a Tasmanian Parks and Wildlife Service Ranger on Macquarie Island whose main role has been to co- ordinate and conduct seabird monitoring. The success of monitoring since this time has significantly increased our understanding of the current status of seabirds on the Island, particularly Grey Petrels, Blue Petrels, White Headed Petrels, Sooty Shearwaters and Soft-plumaged Petrels. Other species that have been monitored as part of this program include Cape Petrels, Diving Petrel Species and Fairy Prions. A monitoring strategy for Rockhopper Penguins has also been formulated and trials were conduced in 2006/7.
Staff from the Tasmanian Department of Tourism, Arts and the Environment (DTAE) in collaboration with staff from the Department of Primary Industries and Water (DPIW) continue to manage the project. On site the PWS Wildlife Ranger coordinates the project, with assistance from other PWS staff. This report covers project activities from the start of April 2006 to the end of May 2007. Last years report, on the 2005-2006 year discussed in detail key threatening processes and potential active management strategies. This report will not cover these in as much detail but it should be acknowledged that these threatening processes are still very much in existence.
Acknowledgements Funding from the federal Department of the Environment and Water Resources, for the Baseline Population Monitoring of Key Seabird Species on Macquarie Island, has enabled a greater emphasis to be put into monitoring of threatened sea bird populations breeding on the Island. We would also like to acknowledge the assistance and support from the Australian Antarctic Division without which the field work for this project would not have been possible. Much of this research has depended on previous work by a variety researchers. Report written by Helen Achurch with input from others working on the project. Edited by James Doube and Sean Thompson. Front cover photo J. Hiscock, J. Doube, and H. Achurch.
1 2. Grey Petrel (Procellaria cinerea)
Photo: Helen Achurch Photo: Helen Achurch
2.1 Objectives of the 2006 season
¾ Monitor breeding activity at known Grey Petrel sites, and document the number of active burrows, breeding attempts, breeding success and failures. ¾ Locate new breeding burrows at existing sites and search for new breeding colonies around the Island. ¾ Document changes in site condition and identify potential threatening processes. ¾ Minimise impact to the sites from monitoring visitation. ¾ Document monitoring program activities over the season and make recommendations for subsequent seasons.
2.2 Background
The Grey Petrel, often described as a large shearwater-like petrel, is circumpolar in its range and breeds on cool temperate and subantarctic islands during the winter (Harrison 1985, Marchant and Higgins 1990). In the Australasian region this species of burrowing petrel is known to breed on the Antipodes and Campbell Islands and more recently on Macquarie Island. It is estimated to have an overall breeding population of between 32000 to 73000 pairs (Bell cited in Schulz et. al. 2005). This large bodied petrel is easily distinguished from other petrels by the combination of its size, slender greenish-yellow bill, uniform ashy grey dorsum and mostly white underbody which contrasts with dark grey underwings and undertail (Marchant and Higgins 1990).
Macquarie Island is the only known breeding location of the Grey Petrel in Australia. It is listed as Endangered by the Tasmanian Threatened Species Act 1995 and has the status of a Marine and Migratory Species in the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999. The Action Plan for Australian Birds (Garnett and Crowley 2000) records the Australian breeding population as Critically Endangered and Bird Life International (2004) lists the Grey Petrel as Near Threatened.
Grey Petrels were first reported breeding on Macquarie Island by J.R. Burton in 1900 (cited in Campbell 1974). The long absence of any subsequent breeding evidence over the next eighty years resulted in the species being regarded as no longer breeding on Macquarie Island (Jones 1980 cited in Rounsevell and Brothers 1984) even though they were still known to visit the area. Coinciding with the final stages of a successful cat eradiation program, in 1999 three burrows were found with evidence of recently fledged chicks, suggesting that Grey Petrels had begun to re-establish breeding colonies on the Island (Schulz et. al. 2005). In May 2000 breeding was confirmed by the discovery of a bird incubating an egg. Monitoring of Grey Petrel activity on the Island has continued since this time. From an early estimation of six breeding pairs (Baker et al 2002), numbers rapidly increased
2 over subsequent years to reach a conservative estimate of 78 pairs during the 2005 breeding season (Hedley 2005).
Figure 2.1 Location of currently known past and present Grey Petrel breeding sites on Macquarie Island and areas of prospecting activity in the 2006 season.
3
2.3 Methods
2.3.1 Status of sites at the beginning of the 2006 season Since 1999 considerable effort has gone into identifying breeding locations around the Island. In 2001 a comprehensive report was produced detailing the location of colonies and documenting breeding activity noted in the 2000 and 2001 seasons (Schulz and Hedley 2001). Robinson (2002), Schulz and Lynn (2003), Carmichael (2004) and Hedley (2005) have since documented breeding activity at these known sties and recorded details of any new locations in subsequent years (See Figure 2.1). In 2003 scientific site markers and photomonitoring markers were put in place at all breeding locations around the Island and site photos have since been taken each season. In 2005 a regular monthly monitoring program was established for sites on North Head, Brothers Point and Green Gorge. Permanent wooden pegs, identifying individual burrows, were put in place on these sites. Laminated site photos with the location of individual burrow and a list of grid references were provided at the beginning of the 2006 season to allow for consistent recognition of breeding sites and burrows.
2.3.2 Monthly Monitoring The bulk of Grey Petrel breeding burrows on the Island are located on sites at North Head, Brothers Point and Green Gorge. The monthly monitoring program in 2006 was based around these three locations (See Figure 2.2). Monitoring of Grey Petrel sites in 2006 began the first week of April during staff changeover at resupply. Undertaking this check together with the previous researcher provided good familiarisation with the location of sites and burrows as well as experience with techniques and methods used during the previous season. These locations were then visited each month from April through to October. An attempt was made to keep the timing of visits evenly spread, but weather conditions caused some variation. Sites were not visited following high snowfall or wet soaking rain. Deep snow obscures burrow entrances and makes navigation around the site difficult, increasing the risk of burrow collapse. Soaking wet conditions increase soil instability so these conditions were also avoided given the risk of burrow collapse and proximity of some sites to steep drops. Days when the soil was frozen were the best for getting around the sites with minimal impact.
2.3.3 Monitoring methods The 2005 Grey Petrel Report (Hedley 2005) identified site instability as one of the biggest issues to be considered when monitoring burrowing petrels over the season. Some sites were noted to be extremely fragile and a cautionary approach was fundamental to minimising damage from human visitation. With this in mind, during 2006 visits were kept to a minimum and some fragile sites or areas were avoided altogether.
Laminated site photos and burrow markers were initially used to identify existing Grey Petrel burrows at each site. Burrows were either marked with wooden pegs or pieces of conduit. Wooden pegs indicated burrows suspected of or used for breeding activity during the 2005 season. Conduit marked burrows that were visited by prospecting birds during the 2005 breeding season. All burrows were initially checked for signs of activity. Suitable habitat on each site and within a 100m radius was also searched for burrows showing signs of activity. In the beginning of the season all suitable habitat on North Head, and when time allowed, other locations around the Island were searched for new areas of breeding activity. In addition to the site photos produced the previous season, mud maps were drawn at the beginning of the season to document new burrows and highlight preferred stable routes around the sites. In this way fragile areas could be avoided.
On each visit prospective burrow entrances were searched for signs of activity. Signs included faeces, digging or tracks in and around the burrow, freshly plucked green vegetation, feathers, and the presence of egg shell, down or birds. When first investigating the burrow, a torch was used to search for evidence down the tunnel. If nothing was found then an imitation of a Grey Petrel call was tried as adults on nests will often respond to calls. If nothing was discovered then a digital camera, held at full arms length, was used to take a photo down the burrow. Using this camera technique, birds were often detected. Photos also provided information on burrow direction for later use of the
4 burrowscope. If the above methods were inconclusive a burrowscope was then used to investigate long or convoluted burrows. The burrowscope’s cumbersome size and weight meant that it was not used during initial burrow checks. Monthly visits, to active burrows, provided a continuum of information on breeding activity at each burrow throughout the season. In some initially uncertain burrows this progressive evidence provided clarification of breeding status. Monthly checks were also useful for detecting previously missed burrows.
Figure 2.2 Grey Petrel breeding sites monitored each month during the 2006 season.
Information from each visit was recorded on a spreadsheet which could be taken out on subsequent visits. In this way previous notes on burrow status, position of burrow, direction of burrow, location of nest chamber, rabbit or human damage etc could be reviewed before burrow checks. Pest species and predator activity, such as number of European rabbits (Oryctolagus cuniculus) seen on site, Black rat (Rattus rattus) faeces near burrow entrances, skua kills and rabbit digging and damage to burrows, was recorded during each visit. Old signs of bird activity, such as skulls and old egg shell were also noted. As the season progressed, previously active burrows conclusively proven to be unoccupied, were removed from follow up visits.
2.3.4 Other locations around the Island Grey Petrel breeding sites around the Island, aside from the ones being monitored each month, were visited on one occasion during the 2006 breeding season. The location of these sites (See Figure 2.1) or their fragility meant they were unsuited to monthly monitoring. These sites were visited between mid August and mid September at times of suitable weather (ie no snow and not too wet). Burrows on these sites are not marked. Each site and surrounding suitable habitat was searched for current and old signs of Grey Petrel activity. Photomonitoring photos and an assessment of rabbit grazing damage were also undertaken during these visits. 5
2.3.5 Site and burrow numbering/marking One of the recommendations from the 2005 season was that the current site numbering system be reviewed and a more consistent approach adopted for the identification of sites and individual burrows. Prior to this time two site numbering systems (original site numbers and scientific site tag numbers) were used inconsistently to identify the sites. Some sites were split into sub groupings, some of which were right next to each other (due to the spreading of active burrows over time), and a number were a considerable distance apart. Identification of the sites has now been standardised so that they are now referred to by scientific site tag numbers. This number is attached to the scientific site marker on each site. Permanently engraved wooden pegs, marking individual burrows, were changed so that they now identify the scientific site and burrow number. Changes were made to some of the sub groupings, neighboring burrows were placed in the same group, outlying groups of burrows were made into subgroups or completely new sites. New sites were given scientific numbers and all changes were updated in the Scientific Sites Database held on the Island. To assist with the transition, the original number has been included in the colony name and details of the changes will be kept on file in the TASPAWS Office on Macquarie Island.
Burrows monitored in the 2005 season were marked with wooden pegs and burrows where birds were though to be prospecting were marked with conduit. In 2006 additional burrows were only marked with wooden pegs when breeding activity was confirmed. When prospecting activity was suspected in a burrow (ie birds visiting the burrow, nest building and digging without a breeding attempt) they were marked with conduit. Wooden pegs, made from treated pine, were engraved with the site and burrow details and placed near the entrance, but in a location that would not interfere with bird activity on the site. Unoccupied burrows used in the past for breeding, but not used this season due to collapse or other damage retained their burrow number. New burrows were assigned the next number at the site. This should help to demonstrate the number of burrows at each site that can no longer be used due to rabbit or erosion damage. Photo: Helen Achurch Photo: Helen Achurch
New nest markers put near burrow entrances 2.3.6 Burrow descriptions Additional information was compiled on most of the active burrows monitored in the 2006 season. Details such as number of entrances, depth of burrow, fraction of concealment of entrance, rabbit damage to burrow, human damage to burrow and a description of burrow direction and approach cautions, were recorded.
2.3.7 Rabbit Grazing Damage Monitoring An assessment of rabbit grazing damage was undertaken at all Grey Petrels breeding colonies during the 06/07 season. The assessment was based on the amount of damage to (including complete removal) the main vegetation community known to have existed on the site in the recent past (approx 5-10 years ago before extensive rabbit damage started on the escarpment slopes). A five point scale, based on the percentage of grazing damage sustained on the site relative to its past condition, was used. For example the scale ranges from 0-20% to 80-100% of original vegetation removed. Site assessments were first conducted last season at the end of the 2005-06 summer. During the 06-07 year assessments were conducted at the beginning of spring as well as at the end of summer where possible.
2.3.8 Photomonitoring Photomonitoring of the Grey Petrel breeding sites was undertaken in July/August/Sept this season when weather permitted good visibility. Methodology is documented in the 2006 Grey Petrel Report. On some sites the original photo marker was missing, where this occurred a new marker was installed using previous photos and details updated on the methodology. Site markers and photomonitoring 6 markers were installed at sites SS#283 and SS#281. Photos were stored electronically with TASPAWS 2006 data under Grey Petrel/photomonitoring. Copies of photos from previous years were also added to this location to enable comparisons of site quality. Additional photos were taken on some sites if the photomonitoring location was thought to no longer represent the whole of the site. Photos were also taken of sub sites (A/B) and areas where site degradation wasn’t shown up on other photos. This was done at the end of the season on monthly monitored sites and in Aug/Sept for the other Grey Petrel sites around the Island.
2.3.9 Search for new breeding colonies When time allowed, suitable habitat was searched for Grey Petrels activity throughout the season. North Head was the main focus for searches, given the quality of habitat and the proximity to other active sites. At the beginning of the season, considerable effort was put into searching potential habitat near known breeding sites on North Head, Brothers Ridge and south of Green Gorge. Active burrows found during this time were marked with conduit and monitored during subsequent visits. Towards the middle of the season, when prospecting birds were investigating burrows, an effort was again made to search for new areas of activity. The location of sites showing signs of activity were recorded by GPS and burrows marked with conduit so that they could be revisited during the next breeding season. Photo: Helen Achurch Photo: Helen Achurch
Prospecting birds found in a burrow in the middle of the season
2.3.10 Collection of eggs and carcasses Abandoned eggs and dead birds were collected when found on the sites. Eggs were measured and candled to note their stage of development when abandoned. They were then blown out and waxed and kept for reference or sent to the Tasmanian Museum. Dead chicks and adults were also collected and put in the freezer until they could be sent back to the Tasmanian Museum.
2.3.11 Monitoring of feral species, predators and other burrowing seabirds on sites Throughout the season the presence of introduced pest species, skuas and other burrowing seabirds, on the sites, was noted. Rabbit, and rat activity was recorded during each visit. An assessment of rabbit grazing damage was also undertaken at each of the sites.
2.3.12 Update Macquarie Island Burrowing Petrel Database Data compiled on the number of active burrows, breeding attempts, chicks fledged and grazing damage percentage for each Grey Petrel site has been added to the Macquarie Island Burrowing Petrel Database.
2.4 Results
2.4.1 Monthly Monitoring Throughout the season 153 burrows were investigated for signs of breeding activity at sites in the three areas being monitored. These burrows included those monitored during the 05 season (marked with wooden pegs), those visited by prospecting birds in the 05 season (marked with conduit) and any new burrows that presented evidence of visitation during the 06 season (marked with conduit). Burrows were monitored each month until definite evidence of a failed breeding attempt was noted or it became unlikely that any evidence of breeding activity was going to be detected. New burrows were initially marked with conduit and checked on subsequent visits. If evidence of breeding was detected then the conduit was replaced by a wooden marker. Later in the season, when birds were detected in new burrows, or in marked burrows that had previously shown no signs of activity, they were monitored during subsequent visits until it was certain that they weren’t a previously missed breeding attempt. These birds were thought to be prospecting burrows for future seasons. 7
Burrows Breeding Burrows Burrow with Success No. of with Confirmed suspected Suspected % marked breeding Breeding but breeding Fledged Failed Prospecting Area burrows Activity attempts unconfirmed Chicks Nests Activity North Head 102 56 43 4 15 28 28 35 Brothers Point 26 16 13 0 0 13 2 0 Green Gorge 25 14 11 3 0 11 3 0 Total 153 86 67 7 15 52 33 22 Table 2.1 Summary of results from monthly monitoring of Grey Petrel Burrows during the 2006 season.
Table 2.1 summarises the results from the 2006 monthly monitoring program. Active burrows included confirmed and unconfirmed breeding attempts and those burrows where birds were active at the beginning of the season but departed without any evidence of breeding. A breeding attempt was confirmed if chicks, abandoned eggs or fresh egg fragments were detected in burrows or at their entrance. Some burrows were suspected of having breeding activity (ie activity throughout the season or birds sitting on nests etc) but no chick, egg or egg fragments were found so breeding was unconfirmed. A successful breeding attempt was defined by the presence of a near fledged chick in shallow burrows or the presence of grey down and a distinctive odour at the entrance of deep or convoluted burrows in early to mid October. Chicks were assumed to have fledged if they were absent from the burrow late in October and no evidence of their death was detected on the site. Nests were recorded as failed if dead chicks, abandoned eggs or egg fragments without any sign of a chick were found. Breeding success was calculated as the number of fledged chicks as a proportion of the total breeding attempts. Burrows were thought to have had prospecting activity if evidence of visitation was first found later in the season (ie after egg laying). Prospecting activity was noted in new burrows or in marked burrows that had shown no previous sign of activity. Further details of the results from monthly monitoring can be found in 2006 Grey Petrel Report. Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Adult Grey Petrel on a nest Grey Petrel chick early in the season Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Chick starting to loose down in September Down left at burrow entrance late in the season prior to fledging
Eggs were detected during the first site visit on the 3rd April, which was an earlier date than previously recorded. (Note as this report is being written eggs were seen on the 28th of March at the start of the 2007 season). The first chicks of the 06 season were seen during site visits on the 6th of June. In total only twenty chicks (dead or alive) were detected in burrows, across all three locations. The North Head sites were the only ones of those being monitored monthly, to successfully fledge chicks (See Table 2.1). Three chicks hatched at the Brothers Point sites, but all died and no chicks 8 were thought to have hatched at any of the Green Gorge sites. Site degradation was thought to be an important factor in this difference.
There were fifty two nest failures across all three sites (see Table 2.1). The majority of these occurred during the egg phase (85%). Eight (15%) of the burrows failed at chick stage. It is possible that the number of failures at chick stage was greater as predators may have removed chick carcasses and only left egg remains. All but one of the dead chicks died within two months of hatching - the exception being one at Brother Point which was thought to have died in the month prior to fledging. It was difficult to determine when most of the egg failures occurred. Abandoned eggs and shell fragments were most often found later in the season when burrows were dug out by birds or when later excavated by rabbits.
2.4.2 Results from other colonies Of the twelve other known Grey Petrel sites around Island, only eight were visited in the 2006 season (see Figure 2.1). The sites at Eagle Point Bluff, West Rock and South Reef were thought to be too fragile to sustain visitation (all these sites had substantial rabbit grazing damage in 2005, see Table 2.5). The remote sites were only visited once in August at a time when any breeding activity should still be evident (except Aurora Ridge which was delayed until September due to inclement weather). Prospecting birds were also likely to be detected at this time. Due to their location and relatively lower levels of activity, these sites weren’t included in the monthly monitoring. Results are summarised in Table 2.2 below and further details are available in the 2006 Grey Petrel Report.
Breeding activity was only confirmed at two locations, Aurora Ridge and Lower Sellick Point and only one chick was thought to have fledged (from the former site). Adult birds, thought to be prospecting, were seen in burrows at two sites. Site condition at most of these sites was very poor, with five out of the eight sites having extensive rabbit grazing damage (ie greater than 60% see Table 2.5). It is possible that Grey Petrel activity at these sites was not detected given the sites were only visited once in the season, however visits did provide an indication of whether breeding sites were still being used.
Confirmed Breeding Active Breeding Chicks Success Site No. Colony Name Burrows Attempt Fledged % Notes Lower Eagle Point Too fragile not visited in ss#92A Bluff (17a) NA NA NA NA 2006 Upper Eagle point Too fragile not visited in ss#92B Bluff (17b) NA NA NA NA 2006 Site fragile with extensive ss#61 Hell Point (10) 0 0 0 0 rabbit damage Lower Sellick Point: ss#178A Ridge (9a) 2 1 0 0 Mid Sellick Ridge ss#178B (9b) 0 0 0 0 Bird seen in one burrow, may have been ss#179 Flynn Point (8) 3 0 0 0 prospecting North Double Point ss#184 (18) 1 0 0 0 Rockhopper Point ss#189 (14) 0 0 0 0 ss#191 Aurora Ridge (16) 11 6 1 17 Adult bird seen in burrow ss#190 Precarious Point (15) 0 0 0 0 Crest of West Rock Too fragile not visited in NA (21) NA NA NA NA 2006 Spur opposite South Too fragile not visited in NA Reef (12) NA NA NA NA 2006 Table 2.2 2006 Results from one off visit to other known Grey Petrel sites around the Island.
2.4.3 Burrow descriptions Additional information was gathered on individual Grey Petrel burrows being monitored over the 2006 season to assist with their future identification and for comparing their condition in subsequent 9 years. Information collected: the number of entrances (including new rabbit tunnels), rough depth (tussock overhang, less than 1m, 1m to 3m and >3m), concealment of entrance (none, 0-1/3, 1/3-2/3 and >2/3), notes on burrow direction and approach directions, rabbit damage over the season, and human damage over the season. The 2006 Grey Petrel Report contains these results as well as information on the success or otherwise of the individual burrow. Further analysis of this data was not undertaken due to time constraints.
2.4.4 Damage to sites and burrows Rabbit grazing damage was assessed at all sites during the 06 season either at the end of winter, beginning of summer or both. Table 2.5 compares 05 and 06 assessments and breeding success results.
During site visits damage to burrows thought to have resulted from rabbit activity was recorded. Of the burrows being monitored, at least 42 out of 107 sustained noticeable damage from rabbit activity. Damage was mainly in the form of burrow widening, creation of new entrances or holes and tunnelling off the main chamber. At a number of burrows roof or side wall collapses were evident. Where practical, active burrows were repaired and at least five burrows were fixed during the season.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rabbit damage at sites, general tunnelling and eventual burrow collapse
Given the fragile state of some of the sites it is likely that human visitation is impacting on site quality. Damage to burrows caused by human activity, was documented during the 2006 season. Three burrows sustained damage to their rooves when conducting monitoring checks on the sites. Only one of the burrows was active when the damage occurred. On all occasions the damage was repairable and the active burrow fledged a chick at the end of the season. General damage incurred when walking around the sites was not as easy to document.
2.4.5 Egg measurements Three abandoned eggs were found at sites over the 2006 season. They were collected and measured. Table 2.3 list the details. Measurements of Grey Petrel egg sizes, contained in Higgins and Marchant (1990), ranged from between 78.4 – 86.1 in length and 52 – 58.0 in width. These measurements were recorded at breeding colonies on other subantarctic islands (Tristan da Cunha, Iles Crozet, Iles Kerguelen, and Marion Is). One egg found this season on Macquarie Island was considerably shorter then the other Grey Petrel eggs and outside the above range. This egg was laid in a Grey Petrel burrow and was fresh when found in May so is unlikely to be from another species of bird. More likely it was an abnormal shaped egg that may have been laid by a young or old individual.
Site Burrow Width Length Number Location Number Date found (mm) (mm) ? ? ? 2005 season 55.2 81.5 SS#60 Brothers Point 11 06/4/2006 55.3 85.9 SS#95 North Head 5 07/7/2006 55.3 79.4 SS#95 North Head 4 04/5/2006 54.5 72 Table 2.3 – Measurements of abandoned Grey Petrel eggs collected during the 2005/6 breeding seasons
10 2.4.6 New breeding burrows and locations During the season suitable habitat was searched for new breeding activity. Proximity to existing sites and potential areas identified by Schulz and Lynn (2003) were the main focus of the search effort. Eight new burrows with confirmed breeding activity were found on existing sites. Only one definite new breeding location was found this season, but a number of areas had signs of activity. The new area, about 25m upslope from SS#54, had one confirmed breeding attempt and three other burrows with signs of activity. As this site was in close proximity to an existing site it was given sub site identification. It is now referred to as SS#54B. Seven other active areas were located, five on North Head, one on Brothers Point Ridge and one on Precarious Point. Activity at these sites was most likely from prospecting birds. Figure 2.3 shows the location or the new areas on North Head and the 2006 Grey Petrel Report contains further details on all new locations.
Figure 2.3 Location of New Grey Petrel activity on North Head.
2.4.7 Rat Rabbit and Skua Activity. Notes were kept throughout the season on opportunistic observations of rat and rabbit activity on the sites. Rat faeces were infrequently noted at sites. The sites above Catchme Cave and at the Tip of North had faeces recorded 2 and 3 times over the season. Rat faeces were also observed on the sites at Brothers Stack and at Rockhopper Point. Given the low occurrence of rat faeces on the sites it was surprising to find that all chick and adult carcasses found during the season appeared to have rat chew marks on them (the lack of bruising or haemorrhage would suggest that these all occurred post- mortem). This would suggest that rat faeces are not a true indicator of rat presence on the sites. Interestingly abandoned eggs found on the sites had not been chewed by rats.
Rabbit activity was also recorded when visiting sites. The Grazing Damage Assessments detailed in Table 2.5 also gives an idea of grazing pressure on the sites. Rabbits were often observed when approaching sites and checking burrows. Rabbits were not often observed in the same burrow as a Grey Petrel but in one instance it was discovered that their tunnelling had blocked a burrow and entombed a live chick. On some sites such as SS#188A, SS#187, SS#55A and SS#95 severe damage resulting from rabbit tunnelling and digging was noted in a portion of the sites. Breeding failures at the egg stage were noted in burrows in all of these portions.
11 Photo: Helen Achurch Photo: Helen Achurch Photo: James Doube
Rabbits were often seen in burrows Rat chew marks were found on dead chicks
Skua activity was mainly observed towards the end of the season when chicks were more likely to be near burrow entrances. No carcasses were found during the season but skuas were often noted flying low over sites during the day.
2.4.8 Sympatric species At the beginning of the season a number of Sooty Shearwater (Puffinus griseus) chicks were observed in burrows on Grey Petrel sites. Grey Petrels were not observed in the same burrows while the chicks were there, but were noted to visit burrows later in the season. There was no evidence to allow any conclusion to be made about the interaction between these two species. Sooty Shearwater and White- headed Petrel (Pterodroma lessonii) activity was noted in some Grey Petrel burrows at the end of the season after chicks had fledged.
2.5 Discussion
Methods during the 2006 season closely followed those undertaken in 2005. For this reason a detailed comparison of the two seasons was possible. Table 2.4 compares breeding activity results.
Active Breeding Chicks Breeding Area Burrows Attempts Failures Fledged Success % 2005 Season North Head 63 47 15 32 68 Brothers Point 23 14 9 5 36 Green Gorge 18 9 9 0 0 Other sites 10 8 4 4 50 Totals 114 78 37 41 53 2006 Season North Head 56 43 28 15 28 Brothers Point 16 13 13 0 0 Green Gorge 14 11 11 0 0 Other sites# 17 7 6 1 17 Totals 103 74 58 16 22 Table 2.4 – Comparison of results from the 2005 and 2006 breeding season
There was a substantial decline in Grey Petrel breeding success between the seasons. This trend was noted across all breeding locations around the Island. In 2006 the sites fledged less then half the total number of chicks fledged in 2005. Although active burrows and confirmed breeding attempts were comparable between the two yeas the number of nest failures was significantly higher in 2006. Only one chick fledged away from North Head in 2006 compared to nine in 2005. The decline in breeding success in 2006 is also clearly illustrated in Figure 2.4 which compares breeding attempts and chicks fledging figures over the past seven seasons.
The above graph compares the number of confirmed breeding attempts and fledged chicks over the seven years since Grey Petrels were discovered breeding again on Macquarie Island (no records of breeding success during 2001 could be found). Although there have been some fluctuations in the number of breeding attempts recorded over this period, overall the number has rapidly increased. The number of fledged chicks has also fluctuated but again, overall, the number has generally increased
12 until 2006. In 2006, despite a high number of confirmed breeding attempts, the number of fledged chicks was substantially lower than those recorded over the two previous seasons. The graph also highlights the 2006 season as having the lowest breeding success (ie the number of chicks fledged as a proportion of confirmed breeding attempts) over the seven years since monitoring started in 2000. This demonstrates that the birds were still breeding at the sites in reasonable numbers but failure rates in 2006 were much higher then previously noted.
90
80
70
60
50 Confirmed Breeding Attempts Chicks Fledged 40 Number of Burrows
30
20
10
0 2000 2001 2002 2003 2004 2005 2006 Year
Figure 2.4- Graph comparing Grey Petrel Breeding Success since the 2000 season.
An obvious influence on breeding success on the Island is the dramatic deterioration in the condition of the sites. This is a difficult issue to quantify and correlate with the downturn in breeding success, but the available evidence implies that breeding sites have significantly deteriorated. Figure 2.5 illustrates the dramatic deterioration of six breeding sites over the last four years. It documents changes in vegetative cover over four years of photomonitoring at six Grey Petrel colonies. At Aurora Ridge, Flynn Point, North Double Point and Precarious Point the rapid deterioration of tussock vegetation is very apparent. At sites at the Tip of North Head and Rockhopper Point the changes have been more subtle. Tussock still remains on these sites but the tillers are cropped shorter and small gaps have started to open up between the plants. There were very few sites that did not show some evidence of site degradation since photomonitoring started in 2003.
Table 2.5 lists Rabbit Grazing Damage Assessments for all Grey Petrel sites in 2005 and 2006. All sites have either remained at the same level of assessment or have been awarded a higher percentage of damage. The levels of assessment are very coarse and a reasonable amount of damaged has to be evident to be awarded the higher categories. The bold figures highlight sites that have increased in grazing damage since 2005. Damage to burrows was noted over the season. Numerous burrows suffered from collapses, rabbit tunnelling or had new entrances opened by rabbit digging.
In both 2005 and 2006, breeding success has been much higher on North Head than all the other breeding locations around the Island. Grey Petrel sites on North Head are generally in reasonable condition with a greater amount of intact vegetation and moderate damage from rabbit activity and erosion when compared to other sites around the Island. For example 65% of sites on North Head had a Rabbit Grazing Damage Percentage of 40% or lower compared to 29% at other sites. Less than a third of the sites on North Head had a Rabbit Grazing Damage Percentage of greater then 60% compared to over half of the sites around the rest of the Island. Although site condition on North Head has deteriorated over the last four years, they are still in better condition than other sites around the island. In 2005 and 2006 North Head Grey Petrels sites experienced relatively higher breeding success than at other locations. 13
Other factors that may have contributed to the down turn in Grey Petrel breeding success in 2006 must also be considered. For example natural variation in environmental conditions at breeding sites and away from the Island may have an influence. Island weather conditions such as the number days with strong wind, was often above average during the winter months in 2006. Factors such as sea surface temperature, currents and storms may have affected availability of prey at feeding locations, as well as the possibility of deaths through interaction with commercial fishing. The Macquarie Island Grey Petrel population has been in a colonising phase since they started to breed again on the Island. It is possible that this down turn is also a natural part of this process (although this is unlikely at this stage due to the birds presumed lifespan). Future monitoring is likely to provide a better understanding of factors influencing these population dynamics.
14 2003 2004 2005 2006 SS#55A Top of North Head
2001 2003 2004 2006 SS#179 Flynn Pt
2003 2004 2005 2006 SS#191 Aurora Ridge
2003 2004 2005 2006 SS#184 North Double Point
2003 2004 2005 2006 SS#190 Precarious Point
2003 2004 2006 SS#189 Rockhopper Pt
Figure 2.5 Photomonitoring at some Grey Petrel sites since 2003
15
Site Site Name Breeding Chicks Grazing Breeding Chicks Grazing Grazing Number attempts fledged Damage attempts fledged Damage Damage 05 05 % 05 06 06 % Aug 06 % March 07 SS#55 A Top of North Head 7 6 60-80 8 2 60-80 60-80 & B SS#54A Above Rockhopper Cave 4 1 0-20 3 0 20-40 20-40 SS#54B Above Rockhopper Cave 1 0 20-40 20-40 SS#96 Mid North Head 11 9 0-20 7 4 0-20 20-40 SS#100 Aerial saddle spurline 3 3 20-40 4 0 40-60 40-60 SS#95 Below old Insect Trap site 7 4 60-80 7 3 60-80 60-80 SS#94A Catch-me-cave 5 4 0-20 1 0 0-20 0-20 SS#94B Catch-me-cave 0 0 20-40 20-40 SS#283 West of Wireless Hill 2 1 20-40 20-40 Track Bend (1c) northern end of Aerial 0 0 80-100 0 0 80-100 80-100 NEW Saddle SS#99 Aerial saddle track 3 2 0-20 4 4 0-20 0-20 SS#98A NW Mawsons Mast 0 0 1 0 20-40 40-60 SS#98B NW Mawsons Mast 1 1 0-20 0 0 20-40 20-40 SS#97 SW Mawson Mast 0 0 0-20 0 0 20-40 20-40 SS#93 Above camp cove 1 0 0-20 0 0 20-40 20-40 SS#56 Western Spurline 2 2 60-80 2 0 60-80 60-80 SS#57 1st spurline sth Western 1 0 60-80 1 0 60-80 60-80 spurline SS#60 Brothers Point Ridgeline 8 5 60-80 8 0 60-80 SS#59A Brothers Stack 5 0 0-20 4 0 20-40 SS#59B Saddle between Brothers 1 0 60-80 1 0 60-80 60-80 Stack and ridge SS#58A Above Rockhopper 0 0 80-100 0 0 80-100 80-100 Colony SS#58B At top of SS colony BP 0 0 60-80 0 0 60-80 1st spurline SS#187 Green Gorge East 1 0 80-100 1 0 80-100 80-100 SS#186 Green Gorge west 0 0 80-100 0 0 80-100 80-100 SS#188A Green Gorge 13a 3 0 60-80/80- 5 0 60-80/80- 80-100 100 100 SS#188B Green Gorge 13b 1 0 20-40 2 0 20-40 20-40 SS#188C Green Gorge 13c 4 0 3 0 20-40 20-40 SS#184 North Double Point 1 0 0 0 80-100 80-100 SS#179 Flynn Point (Mt Waite) 0 0 0 0 80-100 80-100 SS#178A Sellick Point Lower 0 0 1 0 20-40 20-40 Ridge SS#178B Sellick Point Mid Ridge 0 0 20-40 20-40 SS#61 Hell Point 0 0 80-100 0 0 80-100 80-100 SS#189 Rockhopper Pt 0 0 0-20 0 0 20-40 20-40 SS#191 Aurora Ridge 2 2 60-80 6 1 60-80 SS#190 Precarious Point SS190 0 0 80-100 0 0 80-100 80-100 SS#92 Eagle bluff lower and 3 1 80-100 NA NA 80-100 80-100 upper GP-N3 West Rock 1 1 80-100 NA NA 80-100 80-100 GP-N4 Southern Coast 0 0 80-100 NA NA 80-100 80-100 Table 2.5 Comparison of 2005 and 2006 breeding success results and Rabbit Grazing Damage at Grey Petrel sites on Macquarie Island
16 2.6 Recommendations ¾ Continue monthly monitoring of Grey Petrel sites on North Head, Brothers Point and Green Gorge documenting active nests, number of breeding attempts, and the number of chicks fledged. Continue to monitor other accessible breeding sites around the Island less intensively. Monitoring should follow guidelines established in the 2005/06 seasons (See Appendix 7) and a thorough change over should be undertaken between Grey Petrel observers between seasons.
¾ Continue to assess site condition through photomonitoring and Rabbit Grazing Assessments.
¾ If areas within a site or an entire site becomes too fragile then it should be either observed from the site boundary using binoculars, visited less frequently or not visited at all during subsequent years. If site condition starts to improve then visitation of the site should be reassessed. In 2007 sites at Crest of West Rock and Spur Opposite South Reef will not be visited. Sites at Hell Point, Precarious Point, Eagle Point Bluff, Flynn Point and North Double point will be visited using extreme caution. In most instances these sites will be observed from a distance using binoculars. Some sections of sites at Green Gorge (#188A and #187) and Brothers Point (SS#60) will no longer be visited.
¾ In 2006 the remote sites were visited once only in August. This time was thought to be a little late for detecting activity at the sites during incubation and too early for detecting down in burrows prior to chick fledging. In 2007 it is recommended that remote sites are visited for the first time in June. At this time incubation of eggs will have recently finished and evidence of activity during this time should still be observed on the sites. If activity is noted on the sites during this time then a follow up visit should be planed for early September. In early September the chances of detecting down near burrow entrances is greater as chicks are close to fledging. If the site is deemed too fragile in June then no follow up visit will occur.
¾ In 2006, descriptive information (such as depth, number of entrances, entrance concealment, rabbit or human damage observed etc) (See Appendix 2) was collected for individual active burrows. In 2007 this data should be collected again with the possible addition of burrow temperature. This information will better document changes to the site over time.
¾ Undertake feral animal control on sites. Support an Island wide eradication program aimed at removing rabbits and rats from the Island. In the interim until the program gets under way:
• Continue shooting pressure on rabbits on North Head over the winter months. • Erect a rabbit proof fence to prevent migration of rabbits to North Head rabbit control area. • In areas of extensive rabbit digging trial coving the surface of burrows with fencing wire. Secure wire to the ground with pegs and soil. This activity may discourage further digging into burrow and help stabilise existing vegetation.
¾ Investigate the use of triggered infra-red cameras (camera trap) as these would allow non-invasive monitoring of all activity at selected burrows. This would provide much better information on interaction with pest, predator and sympatric species, and also on Grey Petrel behaviour around the burrows (such as confirming fledging).
17 2.6.1 Summary of biological information and monitoring suggestions
Wing Cord (mm) 335-344 (n=6) Large heavy bodied petrel with small head, short wedge-shaped tail, narrow, finely pointed wings and slender bill. Upper parts uniform ashy grey, shading to darker slate- grey on cap and sides of face. Upper wings and upper tail may appear slightly darker Identifying features than grey of upper body. When on the island February to October Not definitely known for Macca, approximately Late Feb to late March (birds were noted in Burrows on the 20th Feb and back in burrows on eggs on the 28th of March. Exodus occurred between these Pre-egg laying exodus dates. first egg seen on Macca 28 March, Laying Egg laying likely to be late march to early April Laying to Hatching Under 2 months First chick seen 23 May (was only one seen) Chicks but a number were noted on the 4th of June. Fledging End of Sept to October. Marchant and Higgins (1990), Monitoring References notes 2005/06 Search for new breeding sites April - May Search for locations of prospecting activity June – August. Visit non monitored sites in June to see if active. Return to active sites in early Recommendations for September to search for signs of breeding Monitoring 2007 success (down or chick)
18 3. White-headed Petrel (Pterodroma lessoni)
Photo: Helen Achurch Photo: Helen Achurch
3.1 Objectives of the 2006 season
¾ Monitor breeding activity at four representative White-headed Petrel breeding sites on the Island by documenting the number of active burrows, breeding attempts, breeding success and failures. ¾ Record the number of White-headed Petrels killed by skuas in the vicinity of these sites and other locations around the Island ¾ Document changes in site condition and identify potential threatening processes ¾ Reduce impacts to the sites by minimising visitation. ¾ Document monitoring program activities and make recommendations for subsequent seasons.
3.2 Background
The White-headed Petrel is a large gadfly petrel that ranges throughout the southern oceans mainly in subantarctic and Antarctic waters. Prominent black eye patches below and in front of the eye on a largely white head is diagnostic and their white underbody and tail (white to pale grey) contrast noticeably with dark grey/brown wings (Marchant and Higgins 1990).
White-headed Petrels breed on subantarctic Islands in the Pacific and Indian Oceans including: Auckland and Antipodes Island, Macquarie Island, Iles Kerguelen and Crozet and possibly Marion, Prince Edward and Campbell islands (Harrison 1985). Macquarie Island is the only location in Australia where they are known to breed and they are listed as vulnerable under Tasmania’s Threatened Species Act 1995, given Marine Species status under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and the Australian breeding population is listed as vulnerable by Garnett and Crowley (2000).
White-headed Petrels nest in burrows and are generally colonial breeders. On Macquarie Island they are primarily found on slopes along the escarpment edge corresponding with the historic distribution of tussock (Poa foliosa) vegetation communities (denser colonies currently found in herbfield, were most likely in tussock grassland before European Rabbit (Oryctolagus cuniculus) Grazing) (Brothers 1984). Burrows may also be found less densely on the plateau in herbfield and feldmark communities. Birds tend to avoid burrowing in wetter soil, flat ground, exposed rocky terrain and areas devoid of vegetation (Brothers 1984). Colonies are distributed widely over more than half the area of the island, but are mainly
20 concentrated in the southern and mid sections. White-headed petrels may also be found in mixed colonies with Sooty Shearwaters (Puffinus griseus).
Birds are absent from Macquarie Island for at least two months during winter. They depart from the Island between late May to early June and return again from early August to mid September. Birds are strictly nocturnal in the breeding season and arrive after dark and leave before dawn. They may be heard calling from colonies after arrival and just before dawn when departing (Warham and Brothers cited in Higgins and Marchant 1990).
Much of the early information on the breeding cycle and habits of this species was collected by John Warham on Macquarie Island between Dec 1959 and to March 1961. Work by Nigel Brothers 1975-1982 added to Warham’s findings and provided information on distribution, abundance and threats. In the early 1960s the White-headed Petrel was considered to be very abundant (Warham 1967). Based on burrow counts between 1975 and 1982, Brothers (1984) estimated the Island’s breeding population at 7850 pairs. White-headed Petrels were heavily preyed upon by feral cats (felis catus) (approx 3000 per year) prior to their eradication from the Island and in areas vegetated by tussock they were also impacted upon by wekas (Galilrallus australis scotti) and black rats (Rattus rattus) (Warham 1967, Brothers 1984). Skuas prey on both adults and chicks during the season but particularly around fledging. Warham (1967) also described the potential impact on the population from increasing rabbit activity. In particular he discussed the removal of stabilising vegetation, erosion and the resulting impacts on breeding sites and burrows.
More recent work by Brothers (2000) in 1999-2000, coinciding with the eradication of feral cats from the Island found burrow activity had increased by about 15% in quadrats used to monitor the species. Extrapolated across the Island’s population this represented an increase of 1200 birds giving a total of 9050 breeding pairs. However with the increase in rabbit numbers since 2003 it is thought the population may be decreasing again (TSU 2004). In December 2003 visits to colonies on Sodomy Ridge and Hill 291 noted little or no burrow activity (TSU 2004).
The original sites at Hill 291 and Sodomy Ridge, previously used for monitoring by Nigel Brothers, were re-established in 2004 so that more intensive monitoring could be undertaken. Prior to 2005, with the exception of early work done by Brothers on these sites, monitoring was done sporadically and little data on breeding numbers is available. Sites were visited at the end of the 03/04 breeding season and at the beginning and end of the 04/05 season. Active burrows were noted at the beginning of the season but at the end of both seasons activity was less obvious except if a chick was seen in the burrow and so the number of chicks fledged was uncertain (Carmichael 2004). In the 05/06 summer a monthly monitoring program was initiated at these sites as part of the Baseline Population Monitoring of Key Seabird Species on Macquarie Island Project. All active burrows within the marked site boundaries were numbered and marked with electrical conduit. Sites were visited monthly from early October 2005 to April 2006.
3.2 Methods
In 2006/7 breeding activity was monitored at four White-headed Petrel sites including two previously monitored sites at the southern end of the Island and two new sites at the northern end of the Island (See Figure 3.1). Sites at Hill 291 and Sodomy Ridge were monitored in 2005/6 as well as in earlier years. Sites at Douglas Point Ridge and Douglas Point Ridge South, were set up and monitored for the first time this season.
Hill 291 and Sodomy Ridge sites were visited late in the 05/06 breeding season (April 2006) during staff changeover at resupply. Visiting the site with the previous researcher provided a good familiarisation with the location of sites and burrows as well as experience with techniques and methods used. The Douglas Point Ridge sites were added to the monthly 21 monitoring program in 2006 as it was suggested that the Sodomy Ridge site be dropped from the program due to its fragility and poor condition. White-headed Petrel activity was noted on Douglas Point Ridge during the Sooty Shearwater census in December 05 and was put forward as an alternative site for monitoring during the 06/07 season. At the beginning of the season searches along the escarpment in the vicinity of Douglas Ridge found a denser White- headed Petrel breeding colony (Douglas Point Ridge South). To increase the total number of burrows being monitored on the Island, this easily accessible and stable site was also included in the monthly monitoring program. At the beginning of the season it was decided that the Sodomy Ridge site would not dropped from the 2006/7 program, but instead would be monitored less intensively.
Figure 3.1 Location of White-headed Petrel sites monitored during the 2006/7 season. All burrows found by Brothers (1984) were between 100 and 300m above sea level.
Monthly monitoring began at all four sites in September 2006 and continued until chicks fledged in April/May 2007. An early visit to the sites during August found few signs of activity. At Hill 291 and Sodomy Ridge most burrows were already marked and these were inspected for signs of activity. Any other burrows on these and the Douglas Point Ridge sites, showing signs of activity, were marked with conduit and numbered. A number of active burrows outside of the marked sites at Hill 291 and Sodomy Ridge were also marked with conduit at the beginning of the season. This was done to increase the overall number of burrows being monitored over the season. These burrows were recorded separately so comparisons could still be down with earlier monitoring work conducted on the original sites.
An attempt was made to keep the timing of visits evenly spread, but weather conditions and other work commitments caused some variation. Sites were not visited following high snowfall (which obscures burrows) or heavy rain (which increases soil instability). Burrow entrances were searched for signs of activity. Signs included faeces, digging or tracks in and around the burrow, freshly plucked green vegetation, feathers, and the presence of egg shell, 22 down or birds. When first investigating the burrow, a torch was used to search for evidence down the tunnel. If nothing was discovered then a digital camera, held at full arms length, was used to take a photo down the burrow. Birds were often seen by this method. Photos also provided information on burrow direction for later use of the burrowscope. If the above methods were inconclusive a burrowscope was then used to investigate long or convoluted burrows. The burrowscope’s cumbersome size and weight meant that it was not used during initial burrow checks. Monthly visits provided a continuum of information on breeding activity at each burrow throughout the season. In some initially uncertain burrows this progressive evidence provided clarification of breeding status.
Because of the sites fragility, burrow monitoring at Sodomy Ridge was initially undertaken from the side of the site using binoculars. Later in the season (February onwards), due to drier conditions and growth of vegetation, it was found that site stability had improved. This allowed a closer inspection of active burrows. During subsequent visits active burrows were revisited only if site conditions were suitable (especially dry).
Information from each visit was recorded on spreadsheet which could be taken out on subsequent visits. In this way previous notes on burrow status, position of burrow, direction of burrow, location of nest chamber, rabbit or human damage etc could be reviewed before burrow checks. Indicators of pest species and predator activity, such as rabbits and rat faeces near burrow entrances, skua kills and rabbit digging and damage to burrows, were recorded during each visit. Skua territories in the vicinity of the sites were also inspected each month for White-headed Petrel carcasses. Signs such as feather spreads, wing sets resulting from skua attacks and boluses were noted when seen on or near the site.
Abandoned eggs and dead birds were collected when found on the sites. Eggs were measured and candled to note their stage of development. They were then blown out, waxed and kept for reference or sent to the Tasmanian Museum. Dead adults were also collected and put in the freezer until they could be sent back to the Tasmanian Museum.
Site photos from reference locations and rabbit grazing damage assessments were undertaken at each site during the season. The new sites were given site numbers and tags and details were noted on the local Scientific Sites register. Data compiled on the number of active burrows, breeding attempts, chicks fledged and grazing damage percentage for each White- headed Petrel site was added to the Macquarie Island Burrowing Petrel GIS Database.
3.3 Results
One hundred and thirty-five marked burrows across four sites were investigated for signs of breeding activity during the 2006/7 season. Table 3.1 below summarises the results. At the beginning of the season burrows were marked if they had been active the previous year or if there were signs of activity at the beginning of this season. A breeding attempt was confirmed if chicks, abandoned eggs or fresh egg fragments were detected in burrows or at their entrance. Some burrows were suspected of having breeding activity (ie activity throughout the season or birds sitting on nests etc) but no chick, egg or egg fragments were found so breeding was unconfirmed. A successful breeding attempt was defined by the presence of a near fledged chick or the presence of grey down from late April to mid May (chicks were presumed to have fledged if they were absent from the burrow at the end of the season and no evidence of their death was detected on the site). Nests were recorded as failed if dead chicks of fledglings, abandoned eggs or egg fragments without any sign of a chick were found. Breeding success was calculated as the number of fledged chicks as a proportion of the total breeding attempts. Burrows were thought to have had prospecting activity if adults were first found later in the season (ie after egg laying and no breeding attempt was detected). Further details are available in the 2006 White-headed Petrel Report.
23 Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
White-headed Petrel chicks observed in February 2007
Site Burrow Breeding No. of Confirmed suspected Success marked Breeding but breeding Prospecting Fledged Failed % burrows attempts unconfirmed Birds Chicks Nests Hill 291 30 19 3 0 13 6 68 Hill 291 Extra burrows* 20 14 0 0 12 2 86 Sodomy Ridge 25 15 0 0 11 4 73 Sodomy Ridge 10 8 Extra burrows* 0 0 7 1 88 Douglas Point 20 9 Ridge 2 2 6 3 67 Douglas Point 30 19 Ridge South 2 2 15 4 79 Total 135 84 7 4 64 20 77 Table 3.1 – Summary of results from monthly monitoring of White-headed Petrel burrows over the 2006 season. (* extra active burrows were marked outside of the site boundaries at the beginning of the season to increase the overall number of burrows being monitored this season)
Activity was first noted on the sites when they were visited in mid September. No activity was seen during an August visit. Burrows were also active in October but were quiet again in early November. Presumably this gap coincided with a pre-egg laying exodus from the sites as birds were observed incubating eggs in mid December. The return date from exodus was not determined but it was likely to be towards the end of November. The first chicks were seen on the 20th of January, two still being attended by adults.
All sites successfully fledged chicks. Sixty nine chicks in total (dead and alive) were detected in burrows, across the four sites. Only twenty nest failures were recorded out of the eighty four confirmed breeding attempts. The majority of failures occurred during the egg phase (75%). Five (25%) of the burrows failed at chick stage, three were taken by skuas when close to fledging and two died in the burrow about a month prior to fledging.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Chicks late in the season prior to fledging
24 The presence of down in burrows and around entrances late in the season was a useful indicator of chick presence in long convoluted burrows where breeding status had not been confirmed. A number of chicks were detected in this way. Down was seen in burrows from mid March through to early May but the highest concentrations were detected during visits at the end of April.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Chick deposits down when moving Chick starting to loose down throughout the burrow
Thirty seven White-headed Petrel carcasses, resulting from skua attacks, were found in nearby skua territories or in the vicinity of the sites over the season. The majority of skua attacks were noted on Hill 291 and in the vicinity of Sodomy Ridge. Due to the occurrence of a large number of burrows in the surrounding area these kills were likely to include birds from outside the marked sites. In a few cases the evidence directly linked deaths to particular burrows on the sites. Skuas were often noted on these two sites, particularly Hill 291, either roosting or actively investigating burrow entrances. Birds appeared to be more vulnerable to skua attacks early in the season or just prior to fledging. Pressure from skuas at this time may relate to reduced availability of other food sources. The sites at Douglas Point Ridge did not appear to get as much attention from skuas. Only two adult birds were taken over the season, one on each site. Skuas were observed flying over these sites but were rarely seen roosting there.
The White-headed Petrel site at Douglas Point Ridge also contained six Sooty Shearwater burrows. These burrows were spread throughout the site, but were mainly located at the top. No interaction between the two species was observed
Rat activity was not noted on any of the sites. Abandoned eggs observed in burrows were left whole and appeared to be untouched by rats over successive visits and no faeces were seen around burrow entrances. Presumably their absence was related to the lack of tussock cover on the sites.
Damage from rabbit activity was very obvious on the Douglas Point Ridge and Sodomy Ridge sites. Extensive grazing and tunnelling have heightened impacts from erosion, increased exposure of burrow entrances to prevailing weather conditions and increasing the incidence of burrow collapse. Tussock plants have been killed and only dead stumps, with sparse or absent ground cover remain on the whole site at Sodomy Ridge and the top half of Douglas Point Ridge site. Although tussock and other vegetation was still present on the lower half of the Douglas Point Ridge site, some areas were noted to be very fragile and extensively affected by burrowing activity and grazing of vegetation. Hill 291 and Douglas Point Ridge South were relatively stable sites in comparison. They both supported a healthy cover of Aceana spp and short grasses (particularly Poa annua) with very little bare earth being exposed. Counts of rabbit faeces near burrow entrances each month indicated that rabbit activity was still relatively very high on these sites. When approaching Hill291 on one occasion sixteen rabbits were counted either on or within 30meters of the sites. The vegetation on these sites appears to be able to withstand heavy rabbit grazing and other activity. Although less susceptible to these impacts, the high level of rabbit activity makes it
25 probable that birds are being affected by rabbits using their burrows. The degree to which interactions between these species impact upon breeding activity is not really known. It is suspected that they compete for suitable burrows and that birds are frequently disturbed by rabbits entering the burrow. Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rabbit in White-headed Petrel burrow Rabbit damage at Douglas Point Ridge
Sodomy Ridge site showing lack of Hill 291 covered by Aceana spp and Vegetation short grasses
Three abandoned eggs were collected from the sites and measurements taken. Table 3.2 lists the details. A further three eggs were seen abandoned in burrows but they could not be retrieved. Date Site Egg Egg Burrow Notes found Length Width 10/1/2007 Douglas Pt Ridge 65.7* 49.2* 289 Irregular shape, South fertile but not incubated for long 10/1/2007 Douglas Pt Ridge 73* 51.6* 009 Not incubated for South long 20/1/2007 Sodomy Ridge 73.9 51.1 8 Abandoned during the early stages of incubation, no development Table 3.2 – Measurements of abandoned White-headed Petrel eggs collected during the 2006/7 breeding seasons. *Rough measurements due to eggs being damaged
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Abandoned egg seen in a burrow Feather spread and WHP carcass at Hill 291
26 Throughout the season when White-headed Petrel remains were found and measurements were taken of wings, beak, head and tarsus where possible. Wing cord was measured using a straight ruler with the wing pressed flat. The right wing was measured when there was a choice. Other measurements were taken using callipers. Results are shown in Table 3.3.
Wing Cord Bill Bill Total Date Location found (mm) Width Length Head Tarsus 18/12/06 East of Mt Ainsworth 306 18/12/06 Base of Sodomy Ridge 306.5 18/12/06 Base of Sodomy Ridge 306.7 18/12/06 Base of Sodomy Ridge 297 18/12/06 Base of Sodomy Ridge 324 18/12/06 Base of Sodomy Ridge 313.5 18/12/06 Base of Sodomy Ridge 18.4 95.8 46.6 20/12/07 South of 4 Ways 301 17.5 38.3 93.4 46.4 5/1/07 West of Prion Lake 303 5/1/07 West of Prion Lake 16.4 94.1 5/1/07 West of Prion Lake 16.7 92.2 19/1/07 2km nth of Hurd Pt JD 292.5 17.1 33.6 88.8 43.8 20/1/07 Base of Hill291 301.1 20/1/07 Base of Hill291 315.8 20/1/07 Base of Hill291 16.9 40.3 95.7 47 20/1/07 Base of Sodomy Ridge 278 20/1/07 Base of Sodomy Ridge 306 20/1/07 Base of Sodomy Ridge 309 20/1/07 Base of Sodomy Ridge 300 20/1/07 Base of Sodomy Ridge 295 20/1/07 Base of Sodomy Ridge 17.5 92.4 20/1/07 Base of Sodomy Ridge 18.1 96.7 20/1/07 Base of Sodomy Ridge 16.3 38.1 93.2 20/1/07 Base of Sodomy Ridge 17.2 96.7 Table 3.3 Measurements taken from White-headed Petrel Carcasses over the 2006-7 breeding season.
3.4 Discussion
Methods during the 2006 season closely followed those undertaken in 2005. For this reason a detailed comparison of the two seasons was possible. Table 3.4 below compares breeding activity results.
Site No. of Confirmed Breeding marked Breeding Fledged Failed Success burrows attempts Chicks Nests % 2006/7 Hill 291 30 19 13 6 68 Sodomy Ridge 25 15 11 4 73 Total 55 34 24 10 77 2005/6 Hill 291 22 8 6 3 75 Sodomy Ridge 20 5 2 3 40 Total 42 13 8 6 58 Table 3.4 Comparison of White-headed Petrel breeding activity results from 2005/6 and 2006/7 seasons
A comparison of results between the two years suggests an overall increase in breeding success this season when compared to 2005/6 (although the sample size is very small). This increase was most marked at the Sodomy Ridge site. Interesting this site displayed the poorest site quality with complete loss of tussock vegetation and much exposed friable soil. 27 Although breeding success was down from the previous season at Hill 291, the number of breeding attempts and successful fledgings was markedly higher. From the beginning of the season greater activity was noted on both sites and additional burrows were pegged out. This was followed by an overall doubling in the number of breeding attempts being recorded and three times the number of chicks fledging.
Similar breeding success was experienced at all sites monitored this season with figures ranging from 67 to 88 percent. Sites varied considerably in condition with extensive rabbit damage and erosion being recorded at two of the four sites. Sites also varied in predation pressures from skuas. This would suggest that these factors may be less influential than others (possibly mild summer weather, plentiful food resources etc) in determining breeding success at the monitored sites this season. Given the level of success recorded at all four sites it is probable that other breeding colonies across the Island also experienced similar success. Due to the limited amount of data available it is difficult to say whether this year’s results are typical or unusual. Increasing the amount of data by monitoring over successive seasons is likely to provide a better understanding of factors influencing the population dynamics.
3.5 Recommendations
¾ Continue monthly monitoring of White-headed Petrels at Hill 291 and Douglas Point Ridge South documenting active nests, number of breeding attempts, and the number of chicks fledged. Prior to undertaking monitoring at Sodomy Ridge and Douglas Point Ridge sides, assess their condition at the beginning of the season and decide whether monitoring will proceed and at what level of visitation. Monitoring should follow guidelines established in the 2005/06 seasons (See 2007/8 version of the Burrowing Petrel Monitoring Methods Manual) and a thorough change over should occur between researchers working on White-headed Petrel at the end of the season.
¾ Continue to assess site condition through photomonitoring and Rabbit Grazing Assessments.
¾ If areas within a site or an entire site become too fragile then burrows should be either observed from the site boundary using binoculars, visited less frequently or not visited at all during the rest of the season.
¾ Investigate the use of triggered infra-red cameras (camera trap) as these would allow non-invasive monitoring of all activity at selected burrows. This would provide much better information on interaction with pest, predator and sympatric species, and also on White-headed Petrel behaviour around the burrows (such as confirming fledging).
¾ Conduct a census of White-headed Petrel breeding colonies around the Island (As was undertaken Sooty Shearwaters in 2005/6). This could be done over more than one season and added to over time. Consult Brothers (1984) for results from earlier census. Start by searching grids which recorded high burrow densities. Search for burrows between mid December and mid Feb (during incubation and early chick stages as the likelihood of finding signs of breeding activity at the front of burrows is much higher. Document all area searched (even if nothing found), name and number each individual site, describe the location of colonies, record grid reference (even if just one burrow), estimate the number of active burrows, map the extent of the colony (GPS points around the perimeter), photograph the site, record grazing damage and other details such as vegetation community and site condition. Add results to the Burrowing Petrel GIS database.
28 3.5.1 Summary of biological information and monitoring suggestions
Wing Cord (mm) 291-332 (n=44) Prominent black eye patches below and in front of the eye on a largely white head, white underbody and tail (white to pale grey) contrast with dark Identifying features grey/brown wings. Absent from the Island June, July and early August 9approx 11 weeks). Arrive back in late August and depart at the end of the breeding season in late May When on the Island to start of June Pre-egg laying exodus Early November Not synchronised, from Mid November to end of Egg laying December Incubation 8 to 9 weeks Hatch mid January to mid February, nestling for Chicks approximately 102 days Fledging Late April to mid May Marchant and Higgins (1990) Brothers (1984) References Warham (1967) Start monitoring burrows late November when birds start to incubate eggs (this would minimise disturbance when birds are setting up burrows etc). Do a second check of burrows in mid December to ensure most incubating birds are detected early in the season. Start monthly checks (ensure a visit occurs late in January and again in mid Feb so most hatched chicks are detected early on) and continue monthly visits till April. Do a final check mid May. Search for other SS colonies around the island. Add to the Burrowing Petrel GIS database. Map Recommendations for 2007 locations of colonies around the Island for program management purposes.
29 4. Sooty Shearwater (Puffinus griseus)
Photo: Helen Achurch Photo: Helen Achurch
4.1 Objectives of the 2006 season
¾ Monitor breeding activity at three representative Sooty Shearwater breeding sites on Macquarie Island by documenting the number of active burrows, breeding attempts, breeding success and failures. ¾ Record the number of Sooty Shearwaters killed by skuas in the vicinity of these sites and other locations around the Island. ¾ Document changes in site condition and identify potential threatening processes. ¾ Reduce impacts to the sites by minimising visitation. ¾ Complete island wide breeding colony census initiated in the 2005/6 season. ¾ Document monitoring program activities and make recommendations for subsequent seasons.
4.2 Background
The Sooty Shearwater is a large solid bodied shearwater which is one of the most numerous tubenoses in the world (Shirihai 2002). They generally inhabit subtropical, subantarctic and Antarctic oceans and migrate to the northern Pacific and Atlantic Oceans outside of the breeding season (Marchant and Higgins 1990). Sooty Shearwaters are uniformly brown/grey in colour with a silvery white panel across the centre of their underwing. Their underside appears slightly paler than above when seen up close. They have a dark long slender bill with only slightly raised nostrils and a downward hook at the tip.
Sooty Shearwater breed mainly on subtropical and subantarctic islands in the Australasian region including off the SE Australian mainland, Tasmania, New Zealand, Macquarie, Chatham, Antipodes, Campbell, Auckland and Snares as well islands off Southern America, the Falklands and a small population on Tristan da Cunha (Shirihai 2002). Their total population was estimated to be in excess of 20 million individuals in the 1980s, but their numbers are thought to be in decline (Shirihai 2002).
Sooty Shearwaters are not listed on the Tasmanian Threatened Species Act 1995 or the federal Environment Protection and Biodiversity Conservation Act 1999 but have an international conservation status of Near Threatened (Bird Life International 2004). Sooty Shearwaters are an international migratory species which are considered a coastal species of Conservation 30 Significance in Tasmania. They are protected under international agreements such as JAMBA and CAMBA.
The population of Sooty Shearwaters on Macquarie Island was estimated to be 1770 breeding pairs in the early 80s (Rounsevell and Brothers 1984). Birds were found breeding at thirty- five colonies distributed around the Island but the highest activity was found in the southern quarter. Sooty Shearwaters are colonial breeders (often in association with other species) who nest in self-excavated burrows or in rock crevices on coastal slopes, ridges and cliff tops in herbfield, tussock grassland or forest. On Macquarie Island all colonies were found among tussock (Poa foliosa) or on grass/herbfield slopes which were once covered by tussock (before grazing by European rabbits (Oryctolagus cuniculus)) (Brothers 1984). Colonies often extend down ridgelines running from the top of the plateau and may be found on lower escarpment slopes. Birds are absent from breeding islands over the winter months. They depart from Macquarie Island at the end of the breeding season in May and return again around late October. Similar to other Procellariids, Sooty Shearwaters depart on a pre-laying exodus early in October to November and lay one egg soon after their return. They incubate for approximately 50 days and chicks hatch mid to late January (Brothers, 1984). Chicks fledge late April to May.
Sooty Shearwaters call on land often immediately after returning to breeding sites and before departure, but sometimes call in flight over colonies. Most calling occurs around twilight and prior to departure at dawn and lots of calling activity is generally noted in the period before egg laying. Photo: Helen Achurch Photo: Helen Achurch
Chick starting to loose down around face
Between 1972 and 1982 Brothers (1984) studied the breeding habits, distribution, abundance and threats to the Sooty Shearwater population on Macquarie Island. The total number of burrows found during these surveys was approximately 1800 and colonies ranged in size from 3 to 500 (Brothers, 1984). Little other work has been done on the Macquarie Island population since this time. In 2005/6 a census of most of the Sooty Shearwater breeding sites (excluding the section of the escarpment from Cape Toutcher to Aurora Point) originally detected by Brothers was undertaken. Thirty five breeding colonies were located during the census and 900 active burrows were counted. Due to site instability, burrows could not be counted at seven of the colonies (DTAE and DPIW 2006). All sites were found to be affected by rabbit activity and many to a substantial degree (The 2006/7 Sooty Shearwater Report gives the Rabbit Grazing Damage figures for all sites).
4.3 Methods
4.3.1 Monitoring at Breeding Colonies Following the 2005/6 census of Sooty Shearwater colonies around the Island, potential sites for long term monitoring of breeding activity were identified. Site instability was the main issue when choosing monitoring sites. The poor condition of most Sooty Shearwater sites meant that few were suited to a monthly monitoring program. Three sites were identified Sandy Bay (ss-8), above Rockhopper Cave on North Head (ss-1) and Rockhopper Point (ss- 20). A preliminary visit was made to these sites prior to the start of the 2006/7 breeding season and it was decided that the Rockhopper Point site, although well vegetated with tussock, was too fragile to sustain monthly visits over the season. For this reason monitoring 31 was only undertaken at the beginning and end of the season. Active burrows were marked out in December and January and then burrows were checked for fledging success in April and the beginning of May. When monitoring White-headed Petrels at Douglas Point Ridge a number of Sooty Shearwaters were found nesting among this colony. These burrows were then monitored over the season and findings added to the Sooty Shearwater results.
The sites at Sandy Bay and above Rockhopper Cave were visited each month from late Oct/Dec 2006 till May 2007. Active burrows were marked out during the first visit to the sites. An attempt was made to keep the timing of visits evenly spread, but weather conditions and other work commitments caused some variation. Sites were not visited following snowfall (which obscures burrows) or heavy rain (which increases soil instability). Burrow entrances were searched for signs of activity. Signs included faeces, digging or tracks in and around the burrow, freshly plucked green vegetation, feathers, and the presence of egg shell, down or birds. When first investigating the burrow, a torch was used to search for evidence down the tunnel. If nothing was discovered then a digital camera, held at full arms length, was used to take a photo down the burrow. Birds were often detected using the camera or photos provided information on burrow direction for later use of the burrowscope. If the above methods were inconclusive a burrowscope was then used to investigate long or convoluted burrows. Monthly visits provided a continuum of information on breeding activity at each burrow throughout the season. In some initially uncertain burrows this progressive evidence provided clarification of breeding status.
Information from each visit was recorded on spreadsheet which could be taken out on subsequent visits. In this way previous notes on burrow status, position of burrow, direction of burrow, location of nest chamber, rabbit or human damage etc could be reviewed before burrow checks. Indicators of pest species and predator activity, such as rabbits and rat faeces near burrow entrances, skua kills and rabbit digging and damage to burrows, were recorded during each visit. Skua territories in the vicinity of the sites were also inspected each month for Sooty Shearwater carcasses. Signs such as feather spreads, wing sets resulting from skua attacks and boluses were noted when seen on or near the site.
Abandoned eggs and dead bird remains were collected and measured when found on the sites. Eggs were candled to note stage of development when abandoned. They were then blown out, waxed and kept for reference or sent to the Tasmanian Museum.
Site photos from set locations and rabbit grazing damage assessments were undertaken at each site during the season. The new sites were given site numbers and tags and details were noted on the Scientific Sites Register. Data compiled on the number active burrows, breeding attempts, chicks fledged and grazing damage percentage for each site was added to the Macquarie Island Burrowing Petrel GIS Database.
4.3.2 Census for Breeding Colonies The escarpment slopes between Cape Toutcher and Aurora Point were searched for Sooty Shearwater breeding colonies to complete the Total Island census started in 2005/6. Methods followed those employed in the earlier season. Previous work by Brothers (1984) was initially consulted to identify the approximate location of known colonies along the escarpment. The census was undertaken late in December and January (as per the previous year). Escarpment slopes including ridges and spurlines were searched if they presented suitable Sooty Shearwater nesting habitat (ie areas currently or historically covered by tussock vegetation). Other areas were scanned with binoculars for evidence of bird activity. When a colony was located all active burrows were counted. Burrows were defined as active if they showed signs of recent occupancy indicated by faeces, diggings, fresh egg shell, seabird smell, and adults or chicks in the burrow. Extreme caution was employed when moving about some the sites due to the fragile state most were in. Burrows were sometimes counted from the side of the site.
The number of active burrows, colony location and description, estimated area covered, site photos and rabbit grazing damage estimates were recorded at each breeding site. No scientific site markers were established for the Sooty Shearwater colonies because sites were mainly on 32 prominent headlands and therefore easy to relocate. Where colonies were located on Grey Petrel sites scientific site markers were recorded. All new records were entered into the Burrowing Petrel GIS database. Throughout the year other areas were opportunistically searched for burrowing petrel colonies. Any additional Sooty Shearwater sites were added to the database.
4.4 Results
4.4.1 Sooty Shearwater Site Monitoring One hundred and thirty-seven marked burrows across four sites were investigated for signs of breeding activity during the 2006/7 season. Table 4.1 below summarises the results. At the beginning of the season active burrows were marked with conduit. A breeding attempt was confirmed if chicks, abandoned eggs or fresh egg fragments were detected in burrows or at their entrance. Some burrows were suspected of having breeding activity (i.e. activity throughout the season or birds sitting on nests etc) but no chick, egg or egg fragments were found so breeding was unconfirmed. A successful breeding attempt was defined by the presence of a near fledged chick or the presence of grey down from late April to mid May (i.e. chicks were assumed to have fledged if they were absent from the burrow at the end of the season and no evidence of their death was detected). Nests were recorded as failed if dead chicks of fledglings, abandoned eggs or egg fragments without any sign of a chick were found. Breeding success was calculated as the number of fledged chicks as a proportion of the total breeding attempts. Burrows were thought to have had prospecting activity if adults were first found later in the season (ie after egg laying and no breeding attempt was detected). The 2006/7 Sooty Shearwater Report contains further details on breeding activity at these sites. It should be noted that the results from the Rockhopper Point site are likely to be less reliable due to the low number of visits over the season. Monthly visits generally provide greater details of breeding activity however due this sites fragility it was decided that it would be monitored less frequently. Consequently some details may have been missed.
Site Burrow Breeding No. of Confirmed suspected Success marked Breeding but breeding Prospecting Fledged Failed % burrows attempts unconfirmed Birds Chicks Nests Sandy Bay 26 7 3 5 5 2 71 Above Rockhopper Cave 48 11 3 5 7 4 64 Douglas Point Ridge 6 4 0 1 3 1 75 Rockhopper Point 57 26 5 0 17 5 65 Total 137 48 11 11 32 12 67 Table 4.1 Summary of results from monthly monitoring of Sooty Shearwater burrows over the 2006/7 season.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Chick early in the season Entrance to a Sooty Shearwater burrow, note lip at front
33
Activity was first noted on the sites in October and November and chicks were thought to have fledged around mid May. Thirty-two chicks were detected in burrows, across the four sites and all of these survived to fledging. Twelve nest failures were recorded out of the forty-eight confirmed breeding attempts. All detected failures occurred during the egg phase. The remains of an adult bird were found in a burrow but it was uncertain whether it had attempted to breed this season.
The presence of down in burrows and around entrances late in the season was a useful indicator of chick presence in long convoluted burrows where breeding status had not been confirmed. A number of chicks were detected in this way.
Figure 4.1 Areas of Sooty Shearwater Activity around Macquarie Island. Identifies colonies located during 2005/6 and 2006/7 census as well as colonies monitored for breeding success this season. Numbers indicate the approximate number of active burrows at each site. 34
4.4.2 Census for breeding Colonies Seven additional Sooty Shearwater Colonies were added to the Burrowing Petrel GIS Database at the end of the season. One was discovered on the top of Brothers Ridge when searching for Grey Petrel colonies and the other six were found while conducting the Sooty Shearwater Census between Cape Toutcher and Aurora Point in December/January. Only one of the seven colonies had been documented during previous work by Brothers (1984). Figure 4.1 shows the location of these colonies and Table 4.2 provides details including location, number of burrows, area and rabbit grazing damaged assessment.
Date Location When Recorded approx # active # Rabbit of visit area burrows breeding Grazing (m2) 2006-07 attempts Damage % 2006-07 15/5/06 Top of Brothers Ridge newly identified 30 6 4 80-100 colony Top of escarpment above Cape newly identified 22/1/07 Toutcher colony 45 9 2+ 80-100 At Grey Petrel Site on Lower slopes of escarpment above the newly identified 30/1/07 North Double Point colony 35 approx 3 ? 80-100 At Grey Petrel Site on lower newly identified 120 30/1/07 coastal slopes of Mt Waite colony 10 1+ 80-100 In the vicinity of the Grey 365 Petrel Site on escarpment newly identified 30/1/07 slopes above Sellick Point colony 34 2+ 40-60 On ridge line running up to newly identified 30/1/07 escarpment behind Hell Point colony 600 approx 34 1+ 80-100 On ridge line running up to top of slope escarpment behind point at Nth located by 80-100, bottom 31/1/07 end of Hell Bay Brothers (1984) 230 56 4+ of slope 40-60 Table 4.2 Breeding colonies found during 2006/7 Sooty Shearwater census.
During the breeding season seven abandoned eggs were found at breeding colonies. These were collected, measured and candled to gauge their state of development. Results are listed in Table 4.3.
Date found Site Egg Egg Burrow Notes Length Width No. Medium a/c, yolk denatured, Rockhopper most likely infertile. Found 15/12/2006 point colony 74.4 47.1 N/A kicked out of burrow Rockhopper Not incubated for long, or 21/1/2007 Point 72.8 51.1 33 infertile as egg not developed Rockhopper 69.5 48.8 38 two thirds developed 21/1/2007 Point Cape Toutcher 76.2 49.61 N/A large air sack and egg membrane 22/1/2007 partially developed Cape Toutcher N/A Half of egg so couldn't do measurements, abandoned late 22/1/2007 as veins along egg membrane North Head white Not incubated for long, or SS#100 star infertile as egg not developed 11/3/2007 78.5 47.2 picket Sandy Bay Not incubated for long, or 22/3/07 76.1 48.9 A134 infertile as egg not developed Table 4.3 Measurements of abandoned Sooty Shearwater eggs collected during the 2006/7 breeding seasons.
35 Evidence of three skua kills was found on the monthly monitored sites over the season, two at Sandy Bay and one at the site above Rockhopper Cave. These kills occurred well before fledging so were likely to be adult breeding or prospecting birds. One bird was killed near the entrance to a burrow that had previously been active on the Sandy Bay Site. Skuas were frequently observed roosting on this site throughout the year. Another Sooty Shearwater wing, resulting from a skua attack, was found at station. Table 4.4 contains the measurements taken from two Sooty Shearwater wing sets.
Photo: Helen Achurch Photo: Helen Achurch
Sooty Carcass after skua attack
Wing Cord Location (mm)* Notes Sandy Bay Sooty Shearwater Site 294 wing set Station, near magnetic zone 290 right wing Table 4.4 Measurements taken from Sooty Shearwater wing sets over the 2006-7 breeding season. *Wing cord was measured with a straight ruler with the wing pressed flat. The right wing was measured when there was a choice
4.5 Discussion
Breeding success figures ranged from 64 and 75% this season. All sites successfully fledged chicks and very few nest failures were recorded. This is the first year of monitoring at these sites so there are no earlier results to compare. Monitoring breeding success in this species was not as straight forward as other species being studied this season. Breeding sites exhibited lots of signs of general activity early in the season and at times it was difficult to link this activity to burrows. Later in the season signs of activity were fewer or absent even when it was known that burrows were still active. Due to the generally long or convoluted nature of Sooty Shearwater burrows, techniques for observing nests (camera and burrowscope) were not always conclusive in determining breeding status in many burrows. Hamilton (2000) discusses the complex geometry of Sooty Shearwater burrows and the inherent problems with accurately determining burrow occupancy. Trials aimed at testing the effectiveness of burrowscopes for detecting Sooty Shearwater nests demonstrated unreliability for providing conclusive results (Hamilton 2000). Burrowscopes are often used because other techniques (such as using sound, smell and sign at entrances or probing down burrows with a stick) are thought to be inaccurate. Consequently results from Sooty Shearwater monitoring should not be considered to be precise. It is highly likely that successful breeding attempts and failures were undetected this season and the actual breeding success may differ from the results presented. Results should still be comparative to future monitoring using the same techniques but they should probably be considered to be an under estimation. Sooty sites are often shared with other burrowing seabird species and it likely some of their activity (especially prospecting) is mistaken for Sooty Shearwater activity. This was particularly the case on the Rockhopper Cave site. Blue Petrels (Halobaena caerulea) were active on the site during the season but their activity was often distinguishable due to the size of their burrows and colour of feathers left in tunnels. Grey Petrels (Procellaria cinerea) returned to the site in February and caused some confusion late in the season and a pair of Soft-plumaged Petrels (Pterodroma mollis) was also discovered prospecting on the site later
36 in the season. Other species did not cause confusion at other sites. Confusion over burrow occupancy is additionally exacerbated by only having a few visits to the sites over the season. Evidence of breeding activity can be removed from burrows by birds, rabbits and rats so frequent visits are important for detecting this information. The rate of visitation this season was set conservatively so that damage to the sites was minimised. With this species it may be useful to reconsider this balance prior to monitoring over future seasons.
Between 1975 and 1982 Brothers (1984) located 35 Sooty Shearwater colonies containing approximately 1777 active burrows. During the census this year between Cape Toutcher and Aurora Point seven colonies were found with approximately 152 active burrows. Only one of these colonies had been identified by Brother’s and no activity was found at Aurora Point, where Brothers had previously recorded a small colony. In the 2005/6 census around the rest of the Island thirty-five colonies were located and 990 active burrows were counted (note that activity could not be counted at seven colonies in the densely occupied southern part of the Island due to site instability). Combining these recent census results suggests that there are currently at least forty-two Sooty Shearwater colonies with 1142 active burrow around the Island. This is 635 fewer burrows than recorded by Brothers during the earlier census, but the uncounted colonies probably account for this difference. Table 4.5 below compares the number of active burrows counted during both round island counts. More than half of the colonies counted in 2005/7 recorded a lower number of active burrows, but at some sites there was a dramatic increase in the number. Shaded figures in the table highlight colonies where a greater number of active burrows were recorded. The total number of active burrows, in colonies counted in both censuses, are also compared in the table showing that the later census only recorded a small number fewer. Unfortunately the large colonies that could not be counted would have made up a third of the overall total, so differences at these locations probably contributed significantly to changes in the overall total.
Number of Active Burrows 1972-1982 Active Burrow Areas (Brothers 1985) 05/07 Census North Head 90 51 Handspike 91 80 Sandy Bay 49 18 Langdon Pt 229 102 Brother Pt Area 90 62 Green Gorge to Saddle Pt 111 87 Aurora Ridge 60 40 Mawson Point 20 35 Cape Star 100 110 Rockhopper Pt 10 85 Precarious Point 100 200 Petrel Peak 40 15 Aurora Point to Cape Toutcher 83 146 Comparable Total 1073 1031 South Coast 590 NA Carrick Bay South 100 NA Table 4.5 Comparison of Sooty Shearwater Census results from Brothers (1984) and 2005/7
From the data presented it is difficult draw conclusions about the differences between the Sooty Shearwater censuses. The comparable totals suggest that Sooty Shearwater activity on the Island was similar during the two counting periods and so superficially suggesting that not much has changed over the time period between. Given the number of small colonies found during the later census which were not recorded in the earlier, it could be suggested that at some point between the two counts the Sooty Shearwater population expanded and these new sites were colonised (although, alternatively, these sites previously may have been missed). An alternative possibility is that subsequent generations may have settled in other breeding
37 colonies, but burrowing petrels generally return to the same sites to breed. However, without a marked population of individuals this can not be investigated.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Sooty chicks close to fledging
Another factor to consider before reading too much into these results is that burrow activity may not be indicative of breeding success. Although activity appears to be comparable, between the counts, the number of young fledging could be quite different. The census techniques varied (Brothers did not have access to a digital camera nor a burrowscope) and individual observer differences between the two counts may have also affected the results.
Photo: Helen Achurch Photo: Helen Achurch
Prospecting bird digging out burrow
Site quality at most Sooty Shearwater sites around the Island was noted to be very poor during the census in 2005/6. Monitoring was undertaken on the only sites thought capable of sustaining monthly visits over the season. Rockhopper Point and above Rockhopper Cave still had a substantial amount of tussock cover and the effects from rabbit activity were not as extensive as other sites. Rabbit damage on these sites was noted throughout the season and there appears to be a cumulative increase in impacts. Rabbit Grazing Damage estimates increased on both sites from 0-20% in 2005/6 to 20-40% this season. The Sandy Bay site is relatively quite stable. Although the vegetation has been modified by rabbit grazing in the past it currently supports mostly short grasses which maintain a continuous ground cover. However, most tall tussock plants on the site have been killed. So even though the site is protected from severe erosion, burrow entrances are still exposed to skuas and weather extremes.
Photo: Helen Achurch Photo: Helen Achurch
Sandy Bay site has lost tall Rockhopper Cave Site is Rockhopper Point site tussock cover due to rabbit starting to be affected by starting to have gaps grazing rabbit grazing between tussock
38
Damage from rabbit activity is extremely obvious at most other breeding colonies around the Island and is likely to be having an impact on Sooty Shearwaters through slope instability, burrow collapse and loss of protective vegetation. The 2006/7 Sooty Shearwater Report details Rabbit Grazing Damage Assessments for most of the Sooty Shearwater colonies around the island. 60% of the sites were assessed sustained greater than 60% vegetation loss. Areas with 80-100% typically have lots of exposed bare areas. Brothers (1984) found during earlier work that rabbits had considerably reduced the Sooty Shearwater population on Macquarie Island by destroying some colonies and reducing others in size through grazing and increased risk of predation by removal of protective vegetation. He also suggested that the two species compete for burrows.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rabbit damage at Sooty Shearwater Sites. Tussock plants have been killed and sites often have very little covering vegetation.
From the lack of carcasses found at colonies and generally around the rest or the Island Sooty Shearwaters did not appear to be heavily preyed upon by skuas. Brothers (1984) also noted finding few Sooty Shearwater carcasses as a result of skua attacks.
Some rat faeces were found at Sandy Bay and Douglas Point Ridge sites, but rat activity did not seem to be extensive. Whole eggs were noted to be left for months in burrows. Brothers (1984) also concluded that the effect of rats on Sooty Shearwaters was likely to be minimal.
4.6 Recommendations
¾ Continue monitoring Sooty Shearwaters during the breeding season at Sandy Bay, above Rockhopper Cave, Douglas Ridge Point and Rockhopper Point documenting active nests, number of breeding attempts, and the number of chicks fledged. At Sandy Bay and Rockhopper Cave consider increasing the frequency of visits to the sites to improve the chances of detecting breeding evidence. Possibly undertake checks each fortnight during incubation and guard phases then go back to every three weeks or monthly until just prior to chick fledging then go to fortnightly checks. At this time chicks may be detected by the presence of down at the tunnel entrance, but this evidence may not last long as the down can easily be blown or washed away. Prior to undertaking monitoring at Rockhopper Point, assess the condition at the beginning of the season and decide whether monitoring will proceed and at what level of visitation. Monitoring should follow guidelines established in the 2005/06 seasons (See 2007/8 version of the Burrowing Petrel Monitoring Methods Manual) and a thorough change over should occur between researchers working on Sooty Shearwaters at the end of the season.
¾ Continue to assess site condition through photomonitoring and Rabbit Grazing Assessments.
¾ If areas within a site or the entire site becomes too fragile then burrows should be either observed from the site boundary using binoculars, visited less frequently or not visited at all during the rest of the season. 39
¾ Investigate the use of triggered infra-red cameras (camera trap) as these would allow non-invasive monitoring of all activity at selected burrows. This would provide much better information on interaction with pest, predator and sympatric species, and also on Sooty Shearwater behaviour around the burrows (such as confirming fledging).
¾ Continue to search for new breeding colonies between known sites, particularly along the escarpment edge. Employ a combination of methods including ground searches and night listening watches throughout the season. Check escarpment and ridgelines between existing colonies. Add information to the Burrowing Petrel Database and map locations to assist Island management and access decisions.
4.6.1 Summary of biological information and monitoring suggestions
Wing Cord (mm) 270-313 n=68 (MI) Uniformly brown/grey in colour with a silvery white panel across the centre of their underwing. Their underside appears slightly paler than above when seen up close. They have a dark long slender bill with only slightly raised nostrils and a Identifying features downward hook at the tip. Arrive back on the Island late October and depart in When on the island May Pre-egg laying exodus Early October to mid November Egg laying Mid November (18th – 20th peak) Incubation Approximately 53 days Chicks Hatch mid January (10th to 26th) Fledging April to May but unknown for Macquarie References Marchant and Higgins (1990) Brothers (1984) Start monitoring of breeding sites at the end of November when birds are incubating then every second week till late Jan. Then visit sites every 3 weeks till late April. Just prior to fledging visit sites every two weeks till mid May. Recommendations for 2007 Search for other SS colonies around the island along program escarpment between areas where already recorded.
40 5. Blue Petrels (Halobaleana caerulea)
Photo: B. Navez WikimediaPhoto: B. Commons Navez
5.1 Objectives of the 2006 season
¾ Search Blue Petrel breeding colonies on the mainland for signs of activity at during the 2006/7 season. Note any active burrows, breeding attempts, evidence of breeding success and failures. ¾ Conduct monthly checks of all Skua territories within 500m of Blue Petrel breeding colonies. Collect Blue Petrel remains and document number and take measurements. ¾ Opportunistically search for Blue Petrel remains in other Skua territories around the Island. ¾ If the opportunity arises during the breeding season, visit known colonies on off shore rock stacks to investigate current status of breeding activity. ¾ Document changes in site condition and identify potential threatening processes ¾ Reduce impacts to the sites by minimising visitation. ¾ Document monitoring program activities and make recommendations for subsequent seasons.
5.2 Background
Although circumpolar in distribution, the only known breeding location for Blue Petrels in Australia, is on Macquarie Island. It is listed as vulnerable under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and vulnerable under Tasmania’s Threatened Species Act 1995. The Australian breeding population has also been described as critically endangered in The action plan for Australian birds (Garnett and Crowley 2000).
Brothers (1984) described six Blue Petrel breeding colonies found between 1975 and 1982 on offshore rock stacks around Macquarie Island (Green Gorge, Hurd Point, Davis Point, Mt Waite, Douglas and Langdon points, and possibly off Caroline Point). Based on these findings he estimated the Blue Petrel breeding population on the Island to be between 500- 600 pairs. At this time there were no known breeding colonies located on the main Island. The Blue Petrel’s small size, and almost year round occupation of burrows has meant that it has been, and still is, particularly susceptible to predation pressures from introduced pest species and Skuas. Brothers (1984) found that predation, primarily by Skuas (who’s numbers are artificially inflated) on Blue Petrels, was one of the main causes of total breeding failure. The number of carcasses found each year on the Island near breeding colonies suggested that the population was maintained by immigration from elsewhere (Rounsevell and Brothers
41 1984). Rat sign was found at all but one of the colonies, and was most evident during breeding.
Coinciding with eradication of feral cats, Blue Petrels were discovered re-establishing breeding colonies on the main Island in 1999 (Brothers 2000). Breeding colonies were subsequently discovered at: the slopes behind Green Gorge Hut, the eastern side of lower Sawyer Creek, the north side of Green Gorge bowl, the tip of North Head, West Rock and the large mainland stack at Davis Point (TSU 2004). Observations of Blue Petrels on the west coast off Eagle Point and Cape Toutcher in 2003 suggested the likelihood of other unknown breeding colonies existing on offshore stacks (Schulz and Lynn 2003). The initial success of Blue Petrels on the mainland was facilitated by the deployment of rat bait stations at six sites. Bait stations were subsequently removed in 2002 due to concerns about attenuating responses of rats to bait in the lead up to a planned whole Island eradication program. Monitoring of the mainland colonies since this time has shown that breeding activity has now started to drop off again (Shultz and Lynn 2003, DTAE and DPIW 2006). In subsequent years large numbers of dead adults have been recorded in the vicinity of breeding colonies and in surrounding Skua territories, and last season only one confirmed breeding attempt was noted at all the mainland colonies. No chicks were thought to have fledged.
5.3 Methods
Of the seventeen Blue Petrel breeding sites recorded on Macquarie Island, eleven were visited this season to check for breeding activity. The other seven sites were located on off shore stacks (5) which were difficult to access or located on the main Island (1) in an area too fragile to visit. (See Figure 5.1). The majority of sites were first visited between the 9th and 15th of November. Due to weather and work commitments the Douglas Point and Langdon Point sites were first visited on the 2nd of December. Skua territories in the vicinity of Blue Petrel breeding locations were opportunistically visited during September and October to locate any Blue Petrel remains. Where possible Blue Petrel remains were identified by the white tip on their tail feathers, wing cord and bill morphology.
Suitable habitat within a 100m of each site was searched for burrows. A visual inspection of potential burrows was undertaken to ascertain whether Blue Petrels were active on the sites. Burrow entrances were searched for signs such as faeces, digging or tracks in and around the burrow entrance, feathers, and the presence of egg shell. A torch and digital camera were used to look further down into burrows. The burrowscope was not used to inspect potential burrows due to their small size and the risk of damage. Old sign, such as petrel skulls and old egg shell were also recorded.
When active burrows were located on the sites, follow up visits were planned for later in the season. Skua territories located within 500m of active sites were searched for Blue Petrel remains each month over the rest of the season. To minimize damage to the sites only one follow up visit was undertaken in early February when successful chicks were likely to fledge. Prior to fledging chicks move closer to their burrow entrance often leaving traces of down.
Photos and Rabbit Grazing Damage Assessments were undertaken during the initial visit to the sites. Signs of predator activity such as feather spreads, wing sets resulting from Skua attacks, Skua boluses, rat faeces, nests and caches, were also noted.
Accessible Skua territories in the coastal zone, especially in the vicinity of the inactive or inaccessible Blue Petrel breeding sites, were visited opportunistically to search for remains over the breeding season. Spotlighting was conducted opportunistically near some breeding sites over the season. All sightings and carcass locations were recorded on the Petrels 2006/7 spreadsheet. The Macquarie Island Burrowing Petrel GIS Database has been updated with this seasons results.
42
5.4 Results
Table 5.1 below contains results from checks carried out at Blue Petrel breeding sites during the 06/07 season. The results from the 05/06 have also been included to allow a comparison of the seasons. Figure 5.1 shows all know areas of Blue Petrel breeding activity and shows locations where birds were observed this season.
Name Name burrows # active 05/06 # chicks fledged 05/06 # breeding attempts 05/06 Grazing % Damage burrows # active 06/07 # chicks fledged 06/07 # breeding 06/07 attempts Grazing % Damage Notes Green Gorge 0 0 0 80- 0 0 0 80- Activity noted in 2001, a rat jaw found on site. Site East BP-1 100 100 decimated by rabbits Caroline Cove Stack BP-2 Offshore stack with Blue Petrels (Brothers 1984)
West Rock 10 0 0 80- NA NA NA 80- Ridgeline BP- 100 100 3 Site not visited in 06/07 area too fragile Hurd Point 0 0 0 80- 0 0 0 80- High numbers in 2001. Some feathers seen in one Stacks BP-4 100 100 burrow but not active. Stacks decimated by rabbits, very fragile. High concentration of rat faeces across site. Davis Pt Main 0 0 0 80- 0 0 0 80- Active in 2001. Nothing seen. Low density of rat Stack BP-5 100 100 faeces and one jaw found. Six rabbits seen on stack. No remains in nearby Skua territories throughout the season. Davis Pt offshore stack BP-6 200-300 in 1980’s (Brothers 1984) Wt Waite offshore stack Location approximate, unsure without GR, ~20 found BP-7 in 1980s (Brothers 1984) Green Gorge 0 0 0 - NA NA NA 0-20 ~20 in 1980s (Brothers 1984). Visited at the end of the offshore stack season (early March) no sign of any activity during BP-8 the season. Blue Petrels had been seen at night flying over site early in the season. Langdon Point 0 0 0 NA NA NA offshore Stack BP-9 100-150 in 1980s (Brothers 1984) Langdon Point 0 0 0 80- 6 0 3 80- Active in 2001. Activity on main stack. All tussock Stacks BP-10 100 100 dead and coastal cushion plant growing over stumps. Douglas Point 0 0 0 80- 51+ 4+ 32+ 20-40 170 in 1980s (Brothers 1984) Active in 2001. Activity Low Tide 100 on main stack only. Numerous burrows with egg shell Stack BP-11 at entrance indicating early failure. Only 70% of stack searched due to fragility. 2 dead chicks, 2 dead fledglings and 1dead adult in burrows. Moderate density of rat scats over the stack Collected 7 Blue Petrel skulls from the site. Mawson Point 0 0 0 0-20 0 0 0 0-20 furthest stack 1 dead bird and chewed skull in 2005. High density of BP-12 rat faeces. Above 5 0 0 0-20 11 0 6 20-40 Active in 2003, 2005. 6 burrows with egg shell Rockhopper present near entrance. Visited each month for Sooty Cave BP-13 Shearwater monitoring. Sawyer Creek 1 0 1 - 0 0 0 60-80 15 burrows in 2003. 50m SW of the site a burrow east slopes- entrance was found with the remains of a Skua attack
43 north BP-15 on a Blue Petrel/prion (species ID couldn't be confirmed) Sawyer Creek 0 0 0 - 2 0 0 60-80 10 active burrows 2003. Two locations (A) feathers east slopes- seen near old burrow entrance that appears to have south BP-16 been dug out by rabbits. Egg shell seen at one entrance. (B) area of activity to the nth (492794 3945775). Feathers, digging and faeces near burrows. A dead adult was found at the entrance of one of the burrows. Rat scats found near dead bird and carcass dragged towards rat tunnel. Green Gorge 0 0 0 40-60 2 0 1 40-60 ~20 active burrows in 2001 Feathers, faeces and fresh attached stack digging at burrows. Site fragile, considerable rabbit BP-17 damage Green Gorge 0 0 0 60-80 2 0 0 60-80 ~30 burrows across large area 2001. Wing set found north facing near the site, tussock no longer present. 2 burrows slopes BP-18 50m from GPS location feathers, digging and faeces near burrows. A dead Blue Petrel was found at the entrance of one of the burrows. Rat scats found near dead bird and carcass dragged towards rat tunnel. Table 5.1 Results from breeding activity monitoring conducted at Macquarie Island Blue Petrel colonies during the 2005/6 and 2006/7 seasons.
Thirty-four Blue Petrel remains from suspected Skua attacks were found this season, either on breeding sites or in territories in the vicinity of these sites. Douglas Point Stack had three kills on site, the Sawyer Creek East Slopes South site had a whole carcass at a burrow entrance and the Green Gorge north facing slope site had one wing set. A Skua territory near Langdon Point had the majority of Blue Petrel remains this season, with twenty-one wing sets and assorted skulls and other body parts. Four sets of remains were found in territories around Green Gorge and Sawyers Creek, two were found at Windsor Saddle and one set of remains at Douglas Stack and the coast near Mt Waite. Throughout the season when Blue Petrel remains were found measurements were taken of wings where possible. Results are shown in Table 5.2.
On three occasions in October and November a number of birds were observed flying around the Green Gorge area, specifically: around the rock stack in front of the hut; near the attached stack; and heading up to the Green Gorge Tarn. Birds were observed with a spotlight and night vision equipment (3rd Generation with IR illuminator). Blue Petrels were distinguished from the numerous prions also active on these nights, by white tail tips and lack of a black streak on the underside of their tail feathers.
Location Wing Cord (mm) Location Wing Cord (mm) Sawyer Creek 216 Langdon Point 218 Sawyers Creek 207 Langdon Point 226 coast below Mt Waite 227 Langdon Point 221 Sawyer Creek 216 Langdon Point 222 Sawyer Creek 215 Langdon Point 213 Langdon Point 205 Langdon Point 221 Langdon Point 215 Langdon Point 213 Langdon Point 211 Langdon Point 216 Langdon Point 218 Langdon Point 206 Langdon Point 221 Langdon Point 213 Langdon Point 209 North of Aurora Cave 210 Langdon Point 211 Table 5.2 - Measurements taken from Blue Petrel wing sets over the 2006-7 breeding season. *Wing cord was measured with a straight ruler with the wing pressed flat. The right wing was measured when there was a choice
44 5.5 Discussion
A greater amount of activity was noted at Blue Petrel sites this season when compared to the 05/06 season (see Table 5.1). Of the twelve sites visited, five showed signs of activity. Breeding attempts were recorded at four sites and a small number of chicks were thought to have fledged from the Douglas Point Low Tide stack. Birds were thought to have had breeding attempts at thirty-two burrows at Douglas Point, compared to none last season. The increased breeding activity at Douglas Point stack coincided with very little evidence of Skua predation on and around the site. Only one Skua territory was located within 500m of the site, and these birds did not appear to target Blue Petrels. The total of thirty-four Blue Petrel remains found near all breeding colonies was far less then the 106 remains found last season and the 115 found in Oct/Nov in 2003. The majority of Skua kills in previous years have been recorded at Douglas and Langdon Points. The reduced evidence of predation by Skuas at Douglas Point, combined with the apparent increase in breeding attempts, suggests that Skuas may be a significant factor inhibiting Blue Petrel breeding.
Figure 5.1 – Blue Petrel activity on Macquarie Island.
Although there was an increase in breeding activity on the Douglas Point Low Tide Stack, this was evidenced by failures during the incubation stage. Egg shell was observed at burrow
45 entrances after birds had cleared out material following nest failures. There was little direct evidence to explain these failures, but it is highly likely that rats played some part either by disturbing nesting birds or by stealing their eggs. Egg shell found on the site had been chewed by rats and there were a number of caches of egg shell near rat nests. There was also a substantial amount of rat faeces across this and many other sites. A small number of burrows at three other sites also had egg shell at their entrance. Two dead chicks, two dead fledglings and one dead adult bird were found in burrows at Douglas Point Stack in early February. It was not possible to determine the cause of death but given black rats are known to prey on small petrels (TSU 2004), it is probable that they were involved in some of these deaths. Seven adult skulls, some with suspected chew marks, were also found on the site. Given rat bait stations set at six of the Macquarie Island colonies in 2000 were thought to have reduced rat numbers and facilitated an increase in Blue Petrel breeding activity at these sites (DTAE and DPIW 2006) and Black Rats are listed as a key land based threat to burrowing seabirds on Macquarie Island in the “The Draft Macquarie Island Burrowing Petrel Recovery Plan 2005-2009”(TSU 2004), it is highly likely that they are still having an impact.
Photo: Helen Achurch Photo: Helen Achurch
Blue Petrel egg shell cached by rats
In addition to rat activity, most of the breeding sites have suffered extensive disturbance from rabbits. Site quality has continued to deteriorate over the last four years due to rabbit tunneling and grazing. Removal of vegetation has exposed surface soils to erosion and many of the sites are now extremely fragile and burrows are at greater risk of collapse. The reduction of vegetation has also left many burrow entrances exposed to the forces of weather and Skua predation. The subantarctic Skua population on Macquarie Island is considered to be artificially inflated, due to high rabbit numbers (Copson 2004), and is likely to be exerting additional pressures on breeding petrel colonies. At least five adult Blue Petrels were killed near burrow entrances by Skuas this season.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Hurd Point Blue Petrel Site Douglas Point Low Tide Stack Blue Petrel Site
Green Gorge was the only offshore colony visited this season but no evidence of activity was detected (despite no sign of rat activity). This visit did not occur until March so signs may have been less evident by this time. It is highly likely that Blue Petrels are still breeding on offshore stacks that are free from rat and rabbit activity. Remains found in Skua territories at
46 Windsor Saddle, and on the west coast near Mt Waite, suggest that Blue Petrels are still visiting breeding colonies near these areas. Unfortunately the impact of Skua predation on these offshore stacks is unknown. Without visiting these stacks during the breeding season, it is difficult to advise on the current status of the whole breeding population on the Island.
Monitoring of known breeding sites, on Macquarie Island, over the last two seasons shows that Blue Petrels are not returning to five of the previously used sites. At the other seven sites breeding activity varied between the two seasons but was much lower than that observed in 2001 and 2003. These results seem to suggest that Blue Petrel breeding colonies on Macquarie Island are highly vulnerable to the impacts of introduced feral species (rat and rabbits) and inflated numbers of Skuas. High predation of adult birds at mainland colonies in combination with very low breeding success is unlikely to be sustainable in such a small breeding population. The absence or decline of breeding activity at many sites is likely to be evidence of this impact.
When inspecting burrows on Douglas Point Low Tide Stack and Green Gorge attached stack, a number of small pieces of plastic were found near the entrances of eight burrows. These plastic fragments were probably swallowed at sea and regurgitated back at the burrow. Plastics ranged in colour, but most were either blue or white. Many petrel species are known to ingest large quantities of plastics which are picked up from the surface of the ocean. Studies cited in the “Recovery plan for Macquarie Island Burrowing Petrels” (TSU 2004) document cases where plastic pellets were found in the digestive tracts of Blue Petrel, Cape Petrel, Wilson’s Storm-Petrel and Grey-backed Storm-Petrel. Ingestion of plastic pellets can cause physical damage to the bird’s digestive system and lead to starvation or may release toxic pollution which can affect the bird’s normal lifecycle (TSU 2004). Chicks are likely to be at a greater risk than adults due to their high rates of ingestion and low frequency of regurgitating indigestible material (TSU 2004). Unfortunately there are few Island management strategies that can influence the ingestion of plastics when birds are away at sea foraging.
Photo: Helen Achurch Photo: Helen Achurch
Small hard plastic fragment at the entrance to a Blue Petrel Burrow
5.6 Recommendations ¾ Protect active colonies from predation by rats and Skuas. o Total eradication of rats and rabbits from the Island. o Put in place interim management measures while waiting for eradication program to take place. Including: Investigate the use of non coumadin baits to control rats at mainland breeding colonies. Eg RatOff® (zinc phosphide) or cholecalciferol based bait. Slow acting and should not cause attenuation to bail problems. Use this technique at all mainland colonies.
47 Alternatively set snap traps (in wire cages) around the perimeter of selected colonies prior to the breeding season. This technique could be trialed at Douglas Point Low Tide Stack, Green Gorge attached stack and Langdon Point stack because these were the main colonies with activity in the 2006/7 season. Set traps for a period (a week) at the end of August and check daily. This is likely to remove resident rats from the colonies and may give an indication of recruitment of new individuals to the area. Set traps as frequently as possible during September. High levels of Blue Petrel activity have been recorded in September (Brothers 1984) prior to breeding. Continue to set traps and check daily as regularly as possible from mid October to early December (birds will be incubation and have small chicks at this time). Monitor breeding activity on sites. If no activity then discontinue trapping. Trial an egg oiling technique in Skua territories near to Blue Petrel colonies to see if this changes predation rates. Once Skuas set up breeding territories in Sept/Oct start conducting regular checks for Blue Petrel remains. If remains start showing up it is likely that the Skuas are preying on Blue Petrels nesting in the nearby colony. If this occurs initiate trial. Oil all Skua eggs in the nest. Oiling will prevent chicks hatching and adults are likely to continue incubating eggs well past the normal hatch date. While sitting on the nest Skuas are likely to continue defending the territory from other Skuas and may prey on fewer Blue Petrels if the necessity for feeding chicks is removed.
¾ Check sites early November and mark active burrows. Markers need to be small and discrete. Return again to sites in early December as at this time failed egg remains are more likely to be detected at the front of burrows. A final visit to active sites in early February to check for signs of chick fledging
¾ Consider a smaller and more flexible burrowscope to inspect burrows. A medical endoscope (with an improvised light source) was trialed in some borrows and found to works well in smaller diameter burrows, such as these.
¾ Remove sign of bird and predator activity after each visit to avoid confused during later visits.
¾ If areas within a site or an entire site become too fragile then burrows should be either observed from the site boundary using binoculars, visited less frequently or not visited at all during the rest of the season.
¾ Continue to assess site condition through photomonitoring and Rabbit Grazing Assessments.
¾ Investigate the use of triggered infra-red cameras (camera trap) as these would allow non-invasive monitoring of all activity at selected burrows. This would provide much better information on interaction with pest, predator and sympatric species, and also on White-headed Petrel behaviour around the burrows (such as confirming fledging).
¾ Attempt boating trips to offshore stacks where breeding activity has been recorded in the past, between late November and early February. Look for signs of Blue Petrel and predator activity. Sites include off shore stacks at: Green Gorge, Langdon Point, Mt Waite, Davis Point, Caroline Cove, Cape Toutcher and Eagle Point.
48 ¾ Continue to search for other mainland breeding areas. Search Skua territories around the Island for remains, spotlight early in the season to find areas of activity, search for burrows in suitable habitat in vicinity of areas of activity and where birds found in Skua territories.
5.6.1 Summary of biological information and monitoring suggestions
Wing Cord (mm) 205-228 (n=130) Square tail, distinguished from prions by white under tail (no black strip) and distinct Identifying features white tip on tail feathers All year but may be absent Jan/Feb if egg When on the Island failed. Most abundant March - May and Sept not known for Macca, possibly early to mid Pre-egg laying exodus Oct first egg seen on Macca 22 Oct, Laying likely Egg laying to be mid to late Oct Laying to Hatching 47-52 days Not know for Macca likely to be early to mid Chicks Dec Not known for Macca, likely to be late Fledging Jan/Feb. Marchant and Higgins (1990) Brothers References (1984) Set rat traps on selected active sites in August through to November. Mark and number active burrows in late Oct/early Nov. Visit sites early Dec to search for signs of egg Recommendations for failure, or active burrows. Visit active sites Monitoring 2007 early Feb to search for signs chick fledging.
49 6. Soft-plumaged Petrel (Pterodroma mollis)
Photo: Jo Hiscock Photo: Jo Hiscock
6.1 Objectives of the 2006 season
¾ Undertake listening watches and spotlighting surveys to determine whether birds are still returning to the island and locate main areas of activity prior to the breeding season. ¾ Conduct ground searches for breeding burrows in suitable habitat throughout the breeding season. ¾ Monitor any active breeding burrows found during the season. Document location and describe sites.
6.2 Background
The Soft-plumaged Petrel is a medium-sized gadfly petrel that is generally found over temperate and subantarctic waters in the South Atlantic, Southern Indian and Western South Pacific oceans (Harper cited in Marchant and Higgins 1990). It is a solid petrel in appearance which is readily identified by a combination of grey underwing and breast band with contrasting white underparts. Its forehead is freckled with white, grey and black and its upper body is characteristically brownish grey with a dark M mark across the upper wings (Harrison 1985, Marchant and Higgins 1990, Shirihai 2002). Two subspecies are recognised, nominate in the Atlantic which is a paler grey with a narrower breast band and a darker form in the Indian Ocean (Shirihai 2002).
The Soft-plumaged Petrel is known to breed on a number of subantarctic and temperate islands including: Antipodes Island, Iles Kerguelen and Crozet, Marion, Tristan da Cunha, Gough Amsterdam, Prince Edward and Maatsuyker Island in Tasmania (TSU 2004). From 1976 to 1979 five wingsets were collected on Macquarie Island, which were later identified to have been those of Soft-plumaged Petrels (Fullagar et. al, 1986). Soft-plumaged petrels are also suspected of breeding on Macquarie Island. They are listed as Endangered under Tasmania’s Threatened Species Protection Act 1995, Vulnerable under the federal Environment Protection and Biodiversity Conservation Act 1999 and critically Endangered by Garnett and Crowley (2000). An extensive amount of spotlighting and listening work was undertaken between July and September in 2003 on Macquarie Island as documented by Schulz and Lynn 2003. This resulted in the identification of numerous locations of Soft-
50 plumaged Petrel activity around the Island (See Figure 6.1). Although nesting had not been confirmed, Garnet and Crowley (2000) estimated that a population of 10 breeding pairs were likely to be present and from the level of calling activity in 2003 Shultz and Lynn suggested that a breeding or prospecting population of at least 42 calling adults may be present (TSU 2004).
Soft-plumaged Petrels generally breed in colonies and nest in self-excavated burrows among tussock grass and ferns on steep slopes and tops of valleys (Marchant and Higgins 1990, Shirihai 2002). Their breeding habits are poorly known and are likely to vary between breeding locations. From observations made at various locations this species is likely to return to breeding colonies around August – September, head off on a pre-laying exodus late November to early December, lay one egg in Nov-Dec, incubate for approximately 50 days and fledge chicks at 90-92 days in April to May.
Figure 6.1 Approximate locations where Soft-plumaged Petrels have been heard and unconfirmed breeding burrow locations, 2000 to 2003 (TSU 2004). Shaded area = approximate area of skycalling; figure associated with each area = maximum number of calling individuals recorded between July and November 2003; X = approximate location of birds in burrows without eggs.
Soft-plumaged Petrels have a very distinctive call. It was well described by John Warham (1979) as low musical moans. Each moan generally lasts 1-2 seconds of a consistent note and
51 then ends with an abrupt increase in frequency (creating a whip like ending). Soft-plumaged petrels were also described by Warham to make a higher pitched squeaking noise and probably a descending staccato call. Birds come ashore at night and call in flight after sunset and again before dawn.
Since the early 1980s, when two calling individuals were observed north of Green Gorge, birds have been suspected of breeding on Macquarie Island. Consistent evidence such as, calling activity throughout the summer season, observation of courting pairs and adult birds observed in burrows, have been recorded over subsequent years. In early 2006 (January) during ground searches following spotlighting, two occupied burrows suspected to be Soft- plumaged Petrel were discovered on the slopes behind Waterfall Bay (DTAE and DPIW 2006). When investigated a bird was briefly seen, before it moved further down the burrow, suggesting it was not on a nest. A later visit revealed that the bird was no longer in the burrow. Follow-up searches at this location, during the following season, discovered an adult Soft-plumaged Petrel siting on a nest in January 2007. A chick was subsequently observed in this and another nearby burrow.
6.3 Methods
6.3.1 Searching for Activity Potential breeding sites and locations of high calling activity identified during previous years were used to plan search locations. At the end of the 2005/6 season (May) escarpment slopes around Brothers Point and Green Gorge were ground searched for any signs of fledging chicks or active burrows. This involved walking up and down slopes searching areas of tussock and other suitable vegetation for signs of activity. Active burrows were likely to have faeces, feathers, down or egg shell near their entrance. Fresh digging and tracks around entrances could also indicate an active burrow. Time restrictions and other work commitments meant that other potential locations could not be searched at this time of year.
Listening watches and spotlighting searches were undertaken opportunistically at all previously known areas of activity between August and November 2006. On some occasions night vision equipment (ITT 160 with third generation or gateless “gen 4” tubes, and 1-3x magnification) was also used to observe calling birds, and an IR illuminator used to locate flying birds at distances >100m (up to 1 km). Searches were not undertaken in extreme weather conditions but an effort was made to search on misty nights with low wind. All calling activity and approximate locations were recorded for subsequent ground searches planned for later in the season.
Ground searches were conducted opportunistically during January and February. This involved searching for active burrows in suitable habitat in the vicinity of all locations where birds had been previously recorded (ie earlier in the season or during previous summers). All patches of good tussock cover on the escarpment slopes were searched near these areas. Photos were taken down any burrows showing signs of activity to see if a bird were present.
Throughout the season skua territories were checked for evidence of petrel predation. Measurements were taken of all Soft-plumaged Petrel remains found during these searches.
6.3.2 Monitoring of active burrows Five burrows suspected of breeding activity were found during ground searches in January and February. The entrances to these burrows were marked with electrical conduit and grid references recorded. Four burrows were marked at a site at Waterfall Bay and one burrow was marked on the slopes behind Green Gorge.
Further monitoring was initiated at these burrows. A second visit occurred two weeks later to confirm the breeding status of a burrow at Waterfall Bay, and then burrows were monitored
52 monthly until April. During April and May visits were conducted every two weeks in an attempt to confirm chick fledging.
Photos were taken of the sites and detailed descriptions were written so that burrows can easily be relocated.
6.4 Results
The calling intensity was greatest at the beginning of the season. The typical musical moan calls were generally heard in groups of three, interspaced by gaps of less than a second. On some occasions a staccato noise was also heard, consistent with that described by Warham (1979). Whilst a bird was not directly observed making the call, it was coming from a flying bird and the only birds seen flying at the time were Soft-plumaged Petrels.
Aerial flights and chases accompanied by extended calls were observed using night vision equipment, particularly in the vicinity of Green Gorge. Soft-plumaged Petrels were noted to be particularly inquisitive towards observers – birds would often hover 3-5m above the observer and investigate sources of light. This activity was generally not detected without image intensification, but they did occasionally call from this location, and on one occasion a bird flew into a head lamp. It should be noted that this lamp was briefly turned on to look at a GPS, and not pointed upward at any stage, suggesting the bird was already very close.
Soft-plumaged Petrel activity was also greater on misty nights with light winds. Activity was reduced on still or very clear nights. Observation and listening was difficult on stormy nights, so their activity then is uncertain.
Figure 6.2 documents where Soft-plumaged Petrels were recorded during the 2006/7 season. Birds were detected by ground searches, spotlighting, listening watches and remains found in skua territories. The 2006/7 Soft-plumaged Petrel Report provides more details on these results. The first birds of the season were heard near Green Gorge on the 15th and 17th of July. Birds were heard or seen with a spotlight or night vision equipment at Waterfall Bay, Green Gorge, Brothers Point, Bauer Bay and on North Head between July and November 2006. One night late in August four birds were observed with night vision equipment in the small tarn behind Green Gorge. They were flying individually around the basin, mostly at low levels near the perimeter, sometimes circling/semi-hovering over the observers. Birds appeared to be interacting in pairs by spiralling around each other in the area to the south east of the tarn (above SS#187). They were not observed landing on the ground at any time.
Ground searches started on the 21 January and were undertaken around other work commitments during the rest of January and February. Suitable tussock slopes near Waterfall Bay, Green Gorge, Bauer Bay and Brothers Point were searched for active burrows. The majority of these locations were completely devoid of tussock and heavily burrowed by European rabbits (Oryctolagus cuniculus). A bird was found nesting in a burrow on the escarpment slope behind Waterfall Bay and a burrow showing some signs of activity was found near Green Gorge (See Figure 6.2). No active burrows were found near Brothers Point or Bauer Bay.
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Figure 6.2 Soft-plumaged Petrel Observation Records for the 2006/7 Season
The nesting bird at Waterfall Bay was detected by taking a photo down the burrow. It was found in the same burrow that a non breeding bird, thought to be a Soft-plumaged Petrel, was seen a year earlier. A chick was found in this burrow two weeks later. On subsequent visits to the site another chick and a failed breeding attempt were detected in nearby burrows. It was uncertain wether the two chicks made it to fledging. They were last seen at the beginning of April and were mostly covered by down (except around the face) and then were gone from the burrows about 3 weeks later. Down was seen at both burrow entrances late in April. A small amount of down was also seen in another burrow but this breeding attempt was not confirmed by other evidence. In summary, 3-4 breeding attempts occurred on the Waterfall Bay site and 2-3 chicks hatched and may have fledged. One nest failed. The 2006/7 Soft- plumaged Petrel Report details results of monitoring visits to these sites. Feathers were found
54 in a burrow near Green Gorge Hut but the activity appeared to be old. The burrow was long and showed signs of rabbit activity. A photo down the tunnel did not show any further sign. No other activity was observed at this site over the rest of the season.
Photo: Jo Hiscock
Soft-plumaged Petrel site at Waterfall Bay showing location of active burrows
A pair of Soft-plumaged Petrels were observed in a burrow on a Grey Petrel site above Rockhopper Cave, North Head (SS#54A) towards the end of April (See Figure 6.2). Given the time of season and the lack of other signs it is likely that these birds were prospecting. The burrow has been marked and will be visited next season.
Photo: Helen Achurch Photo: Helen Achurch
Prospecting pair of birds found in burrow on North Head in April 2007
Remains of four Soft-plumaged Petrels were found in various locations throughout the season. Table 6.1 gives details of the wing cord measurements and Figure 6.2 identifies where they were found.
Wing Cord Date Location (mm)* Notes 12/12/06 Station, Razor west beach 259 Beach washed wing 10/1/07 Bauer Bay Beach 254 left wing found near Blue Petrel 2/2/07 Douglas Point stack 265 colony 14/4/07 Mid North Precarious Bays 265 beach wash, killed by skua Table 6.1 Wing measurements taken from Soft-plumaged Petrel remains found during the 2006-7 breeding season. *Wing cord was measured with a straight ruler with the wing pressed flat. The right wing was preferentially measured when there was a choice.
55 6.5 Discussion
Soft-plumaged Petrels have been suspected of breeding on Macquarie Island since a pair was seen courting in the early 1980s. Breeding was finally confirmed this season when an adult bird was observed incubating an egg. It is highly likely that the birds have been breeding on the Island prior to this discovery as they have been consistently heard calling and observed over at least the last five years at breeding times. A number of non nesting birds have also been observed in burrow. This species is known to be vulnerable to predation from feral cats (felis cattus) and black rats on other islands (Shirihai 2002) and it is highly likely that they have also been exposed to the same pressures on Macquarie Island. With the eradication of cats one potential threat was removed, but rat activity may still be impacting upon the population. Skuas also prey on this species as is evidenced by the ongoing collection of wing sets found in their territories. What impact this has on the overall population is unknown but the number of skuas on the Island is thought to be artificially inflated due to rabbits. This change may have some repercussions for small species of Petrel, such as the Blue and Soft- plumaged, which are easy prey for skuas. Soft-plumaged Petrels generally nest among tall coastal vegetation including ferns and tussock grasses (Marchant and Higgins 1999). Presumably this type of vegetation affords them some protection from predators and shields their burrow from weather extremes. Given the rapid decline in availability of tussock vegetation on Macquarie Island due to rabbit grazing, it is very likely that any Soft-plumaged Petrel breeding sites are being detrimentally impacted upon. The possibility for in-burrow interaction with rabbits to negatively affect these smaller petrels (such as disturbance of incubating adults and chicks) should not be discounted, particularly given that rabbits were noted to be in breeding burrows on two occasions.
Given the highly distinctive and load call, combined with the inquisitive behaviour, it is likely that the detection rate of these petrels is significantly higher than that of many other species. As birds can often be individually located when calling, it is probable that most calling birds in the regularly visited areas would be heard. If this number of calling birds is representative of the breeding population, it would suggest that the numbers of Soft-plumaged Petrels breeding on Macquarie Island is very low (in contrast to birds simply being overlooked due to cryptic behaviour).
6.6 Recommendations
¾ Undertake monthly monitoring of Soft-plumaged Petrels at the Waterfall Bay site and attempt to record the number of breeding attempts, and chicks fledged. Through the timing of visits to the site attempt to clarify details on breeding cycle ie Rough estimates of when birds return from pre laying exodus and when eggs are laid, rough duration of incubation, chick hatching and fledging dates. e.g. From this season we know that a bird was incubating on the 21st of Jan and 16 days later an unattended chick was seen. A visit timed for the end of Feb may provide a more accurate hatching date. Monitoring should follow guidelines established for other Petrel species in the 2005/06 seasons (See 2007/8 version of the Burrowing Petrel Monitoring Methods Manual) and a thorough change over should occur between researchers working on this species at the end of the season. Given the probable very low numbers, it is particularly important that breeding birds are not disturbed during more sensitive times. For this reason inspections of possible breeding burrows should probably be delayed until the incubation phase should have started (after late December).
¾ Assess site condition at Waterfall Bay throughout the monitoring program. Monitor impacts from human visitation to the site as well as impacts from rabbits and predator activity. Once tussock surrounding the site has been checked for active burrows
56 approach site from the scree slope to the south rather than through the vegetation. If the proposed rabbit eradication program is delayed, consideration should be given to fencing this site as rabbit activity and damage is already prominent (and the site could be easily fenced and the rabbits removed during winter).
¾ If areas within a site or the entire site becomes too fragile then burrows should be either observed from the site boundary using binoculars, visited less frequently or not visited at all during the rest of the season.
¾ Investigate the use of triggered infra-red cameras (camera trap) as these would allow non-invasive monitoring of all activity at selected burrows. This would provide much better information on interaction with pest, predator and sympatric species, and also on Soft-plumaged Petrel behaviour around the burrows (such as confirming fledging).
¾ Continue to search for new breeding colonies. Employ a combination of methods including spotlighting and night listening watches early in the season to determine areas of high activity. Expand the area of investigation away from already known locations of activity (spotlight and listen along more remote stretches of the coastline). Devote more time to ground searches in potential habitat looking for active burrows. Use night vision scope if possible. Prioritise search effort so that areas of high activity are searched first.
¾ Brief other expeditioners on the call of this species (play recording or call), and encourage the documentation of calls heard. This will provide a useful log of Soft- plumaged petrel activity in the vicinity of the field huts.
6.6.1 Summary of biological information and monitoring suggestions
Wing Cord (mm) 233-276 n=205(other islands) 254-265 n=4 (MI) Identified by a combination of grey underwing and Identifying features breast band with contrasting white underparts. Arrive back on the island July to September and When on the island possibly depart April to May Pre-egg laying exodus Late November to early December Egg laying November to December Incubation Approximately 50 days Chicks Hatch late January to early February Fledging April to May but unknown for Macquarie Marchant and Higgins (1990) Brothers (1984) References Warham (1967) Listening watches and spotlighting August through to November on suitable evening. Start monitoring burrows at Waterfall Bay late November when birds start to incubate eggs (this would minimise disturbance earlier when birds are setting up burrows etc). If birds not yet back revisit a week or so later until activity is detected. Monthly monitoring can then be initiated. Monitoring could increase in frequency in April so that an approximate fledging date can be determined. Undertake ground searches for breeding burrows Recommendations for 2007 around the island from mid December through till program Feb.
57 7. Cape Petrel (Daption capense), Antarctic Prion (Pachyptila desolata), Fairy Prion (southern) (Pachyptila tutur subantarctica) and Diving Petrel sp (Pelecanoides sp)
Photo: Diving PetrelDoube / James Photo: Cape Petrel / Wikimedia C
Photo: Antarctic Prion / James Doube
7.1 Objectives of the 2006 season
1. Undertake listening watches and spotlighting surveys to detect the presence of these species during the breeding season and locate main areas of activity. 2. Conduct searches for breeding sites in suitable habitat throughout the breeding season.
7.2 Background
7.2.1 Cape Petrel The Cape Petrel is an easily identified medium sized petrel, with a dappled back and white pattern across its upperparts and white underwing and body. They are circumpolar in range and are widely distributed throughout the Antarctic and subantarctic. Two subspecies are recognised, one from the New Zealand islands and the other from elsewhere (Marchant and Higgins 1990). Cape Petrels breed on numerous Antarctic and subantarctic islands across their range generally from November to May (Shirihai 2000). In Australia they only breed on Heard and Macquarie islands. The Cape Petrel is listed as a Marine Species under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and it is to be reviewed under Tasmania’s Threatened Species Act 1995. Garnett and Crowley (2000) describe the Australian breeding population as Vulnerable.
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The Cape Petrel was recorded breeding on off shore stacks off North Head (Anchor Rock and Gorilla Head Rock) in 1951 and 1959 (Gillham 1967). The first confirmed breeding of this species on the mainland of Macquarie Island was in the summer of 2002/3 when two pairs were recorded nesting on the tip of North Head (Clark and Robinson cited in TSU 2004). In November 2003 six nests were located on ledges and open rock crevices around the same location (Schulz and Lynn 2003). Also during this year a bird was seen siting on a nest scrape on the north-east facing ledge of a rock stack off Aurora Cave and extended flight activity was recorded over an outer stack off Hurd Point. Nesting was not confirmed at either location. Cape Petrels had not been recorded breeding on Macquarie Island prior to these sightings. Between the 1970s and late 1990’s several pairs had been observed prospecting in the vicinity of the tip of North Head but no breeding activity was detected. Since 2003 Cape Petrels have not been recorded nesting on the Island.
7.2.2 Antarctic Prion Antarctic Prions are blue/grey on their upperparts with a distinct black M across their wings, and they are white on their underside except for a black streak in the centre of their tail. They inhabit Antarctic and subantarctic waters mainly in the Indian, Southern and Atlantic oceans (Marchant and Higgins 1990). They breed on a number of Antarctic and subantarctic islands including Macquarie and Heard islands. The Antarctic Prion is listed as a Marine Species under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and it is to be reviewed under Tasmania’s Threatened Species Act 1995. Garnett and Crowley (2000) describe the Australian breeding population as Vulnerable.
Antarctic Prions are the most abundant burrowing petrel species breeding on Macquarie Island. Brothers (1985) estimated their total breeding population to be 48 900 breeding pairs based on work between 1975 and 1982. Historic evidence suggests that the Antarctic Prion population has declined since the early 1900s (Burton 1900 cited by Cumpstons 1968, Falla cited in TSU 2004). The decrease is thought to be related to impacts from introduced species, primarily predation by Wekas (Galilrallus australis scotti) and feral cats (Felis cattus) (Brothers 1985). The majority of burrows are currently located on the plateau in herbfield and show a preference for areas dominated by dense Acaena sp cover. Antarctic Prions breed over the summer, returning to the Island from the middle to late October and departing again from mid to late April. Eggs are generally laid in December and hatch around the end of January (Brothers 1985).
Photo: Helen Achurch Photo: Helen Achurch Photo: James Doube
Antarctic Prion in Burrow Antarctic Prion
7.2.3 Fairy Prion (southern) Fairy Prions are blue/grey on their upperparts with a distinct black M across their wings and a wide black terminal band across the upperside of their tail. They are white underneath except for a back streak in the centre of their tail. They are found in subtropical and subantarctic waters and are abundant off south east Australia, New Zealand and in Indian Ocean waters
59 (Marchant and Higgins 1990). They breed on subtropical and subantarctic islands including Tasmania and Macquarie Island.
There is debate over the taxonomy of prions. Some authors have identified two subspecies of Fairly Prion, the northern large-billed and the southern stout-billed (Harper, Marchant and Higgins cited in TSU 2004). Others treat Fairy Prions as monotypic, forming a super-species with the Fulmar Prion (TSU 2004). The validity of the stout-billed form has been questioned (Cox cited in TSU 2004) and it is difficult to distinguish from the Fulmar Prion.
The Fairy Prion is listed as Vulnerable under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and it is Endangered under Tasmania’s Threatened Species Act 1995. Garnett and Crowley (2000) describe the Australian breeding population as Endangered.
Although first recorded on Macquarie Island in 1956 (Keith and Hines cited in TSU 2004) confirmed breeding activity was not recorded until 1979 on rock stacks at Davis and Langdon points (Brothers 1985). Birds were found nesting in rock crevices, in hollows beneath cushions of Colobanthus muscoides and in burrows in peaty soil (Brothers 1985). Since this time birds have been confirmed nesting on the main Island following the observation of a nest by Brothers (2000) and a chick found in Rockhopper Cave at the tip of North Head in 2001 (DTAE and DPIW 2006). Unfortunately, a major storm in 2003 modified the area of Rockhopper cave where birds had previously been found nesting. Twenty abandoned eggs, suspected to be Fairy Prion, were found in a cave at Brothers Point in 2002 (DTAE and DPIW 2006). Birds have not been recorded nesting on the main Island since, although they have been observed while spotlighting at Eagle Point in 2003 (Schulz and Lynn 2003) and flying over the Isthmus in November 2006. Based on earlier findings their numbers on Macquarie Island have been estimated to be between 50 and 250 adult individuals (Garnett and Crowley 2000 and Baker et al 2002). They are likely to breed between September and March.
7.2.4 Diving Petrels Two species of Diving Petrel occur in the Australasian region, the South Georgian Diving- Petrel (Pelecanoides georgicus) and the Common Diving-Petrel (Pelecanoides urinatrix). They are similar in appearance and cannot be distinguished at sea. Both are small and stocky in appearance, black above and white below. They have small rounded wings, a short tail and short cobalt blue coloured legs (Marchant and Higgins 1990). Their flight is generally direct with rapid whirring movements (Shirihai 2002). Both species of Diving Petrel are circumpolar in distribution. The South Georgian Diving Petrel has been recorded breeding on Prince Edward and Marion islands, Codfish Island off New Zealand, Auckland, South Georgia, Heard, Kerguelen and Crozet islands (Shirihai 2002). Three nests were also found on Bishop and Clerk Islets, south of Macquarie Island in 1993 (Brothers cited in TSU 2004). The Common Diving Petrel breeds on a number of subantarctic islands including Heard and Macquarie, as well as Tasmania and a number of New Zealand’s offshore islands. Both species of Diving Petrel are listed as Marine Species under the federal Environment Protection and Biodiversity Conservation (EPBC) Act 1999 and neither are currently listed on Tasmania’s Threatened Species Act 1995. Garnett and Crowley (2000) describe the Australian breeding population of South Georgian Diving Petrels as Vulnerable.
There has been confusion with some historic records identifying the species occurring on Macquarie Island, but both are reported to be present in small numbers on off shore stacks (Brothers 2000). Although first observed in the early 1900s (Campbell cited in Brothers 1984), the Common Diving Petrel was first recorded breeding on Macquarie Island in 1979 on a rock stack at Langdon Point. Their population was then estimated to be approximately 20 breeding pairs (Brothers 1985). One fully fledged South Georgian Diving Petrel chick was found amongst tussock at the southern end of the Island in December 1999, but the breeding
60 population on Macquarie Island is unknown (Brothers 2000). Both species breed in burrows generally on coastal slopes, cliffs and ridges.
Photo: James Doube Photo: James Doube
Diving Petrel found roosting on ground on North Head Sept 06
7.3 Methods
7.3.1 Cape Petrel North Head was visited once monthly when undertaking Grey Petrel and Sooty Shearwater monitoring from October through to May. While working on North Head, especially around the Northern Tip, time was taken to look over breeding areas for recent signs of activity. In October and November the area between Goat Bay and the tip of North Head were thoroughly searched for nesting birds. No other areas around the Island were specifically searched for Cape Petrel breeding activity but all observations of birds were noted. Offshore activity was also noted opportunistically whilst boating.
7.3.2 Antarctic Prion No specific monitoring of this species was undertaken this season. Antarctic Prions were recorded opportunistically when observed during spotlighting. The locations of remains resulting from Skua (Catharacta Antarctica spp lonnbergi) kills were recorded over the summer. Throughout the season when Antarctic Prion remains were found, measurements were taken of wings, beak, head and tarsus where possible.
7.3.3 Fairy Prion Mainland breeding locations at Brothers Point and Rockhopper Cave were searched early in October and again in March for evidence of breeding activity. Catch Me Cave and smaller caves at Brothers Point were also investigated at this time. Searches were conducted early in the season before Rockhopper Penguins started nesting and follow up searches were undertaken after penguins had left. Roof ledges and walls were scanned with a spotlight looking for nests or signs of Prion activity such as faeces, nest material and feathers.
7.3.4 Diving Petrels No specific searching for these species was undertaken this season. Diving Petrels were recorded opportunistically when observed during spotlighting or use of night vision equipment. Skua territories were searched for remains throughout the year. Measurements were taken of wings where possible.
7.4 Results No evidence of any breeding activity was found for the Cape Petrel, Fairy Prion or either species of Diving Petrel although observations of all species were made during the season. Table 7.1 below documents these sightings.
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Number Detection Date Species Location seen Method Notes A pair observed flying together off the Tip of North Head and circling Gorilla Gorilla Head Rock, Visual Head Rock and flying off north from the 04/9/06 Cape Petrel North Head 2 observation Island. Visual 14/9/06 Cape Petrel Camp Cove 1 observation Off shore near Camp cove A pair of birds seen circling the eastern side of the tip directly across from Gorilla Head Rock. Flying low to Visual ground and then circling out and back 04/10/06 Cape Petrel Tip of North Head 2 observation again Visual 18/10/06 Cape Petrel Camp Cove 1 observation One bird seen off shore. Visual A number seen flying between 100 and 21/11/06 Cape Petrel Off shore 1+ observation 200m off shore from tourist ship Visual A number seen flying between 100 and 22/11/06 Cape Petrel Off shore 1+ observation 200m off shore from tourist ship Visual One bird seen off shore from Hurd Pt 24/11/06 Cape Petrel Off shore 1 observation during boating trip Visual Along northern 2/3 of east coast during 9/1/07 Cape Petrel Off shore 5-10 observation boating trip. Diving Wireless Hill North Birds were seen on the ground near the 23/9/06 Petrel sp. Head 2 Spotlighting eastern escarpment edge. Flying 15m off ground, mid way Diving North Head - between escarpment and shore, heading 29/9/06 Petrel sp. Aerial Cove 1 Spotlighting towards ocean. North Head - Diving escarpment above Heard calling from escarpment slope 29/9/06 Petrel sp. Aerial Cove 1 Heard calling above Aerial Cove Diving Catch-me 29/9/06 Petrel sp. Cave/Camp Cove 1 night vision flying low Diving flying low near far northern end of 29/9/06 Petrel sp. Garden Cove 1 night vision Garden Cove Diving 29/9/06 Petrel sp. Razorback west 1 night vision flying low on western side of Razorback Diving Wireless Hill North Remains found in a Skua Territory 26/12/06 Petrel sp. Head 1 Remains Wing cord of 114mm. Bird observed flying over the Isthmus Visual by Dion Hobcroft (bird guide on tourist 22/11/06 Fairy Prion Isthmus 1 observation ship) Table 7.1 – Observations of Cape Petrels, Diving Petrel sp and Fairy Prions over the 2006/7 season.
Remains of sixty Antarctic Prions killed by Skuas were observed over the season. Kills were frequently made around dense concentrations of Prion burrows. Skuas were often seen investigating burrow entrances and sometimes digging away vegetation. Measurements were taken of wings, beak, head and tarsus where possible. These are listed in Table 7.2 below.
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Wing Cord Date Location (mm)* Notes 10/11/06 Sawyers Creek Green Gorge 202 found in skua territory 8/12/06 Lake Flynn 198 Right wing 14/12/06 Jessie Nichol Track 192 14/12/06 Red River near falls 181 right wing 20/12/06 GG south rabbit count 193 Left wing 20/12/06 Nth end GG basin 191 Right wing 5/1/07 Prion Lake 184 6/1/07 Brothers Valley 185 right wing 19/1/07 Nth of Nthern Tio junction 182 left wing 20/1/07 Base of Hill291 187 22/1/07 OLT in Jessie Nicole Basin 192 found in skua territory 29/1/07 Nth of Green Gorge Tarn 191 found in skua territory 30/1/07 OLT sth of GG 186 right wing 30/1/07 OLT Nth of Pyramid Peak 187 30/1/07 Southern side of Flynn Lake 179 found in skua territory 30/1/07 Southern side of Flynn Lake 185 found in skua territory Slopes west of Green Gorge 1/2/07 Tarn 185 found on slope 10/2/07 Bauer Bay Beach 192 right wing 10/2/07 Bauer Bay Beach 181 left wing Table 7.2 Wing measurements taken from Antarctic Prion remains found during the 2006-7 breeding season. *Wing cord was measured with a straight ruler with the wing pressed flat. The right wing was measured when there was a choice.
7.5 Discussion
With so few sightings of Cape Petrels, Diving Petrels and Fairy Prions it is difficult to interpret much about their current breeding status on Macquarie Island. Following the eradication of feral cats, Cape Petrels and Fairy Prions were found breeding for the first time on the main Island. Unfortunately subsequent monitoring indicates that neither species has returned to these known breeding locations since 2003. Factors such as storm damage and disturbance by black rats are thought to be probable causes for the halt in colonisation at these sites. This is not to say that they are not breeding on off shore stacks or in isolated areas on the mainland. Continued monitoring of known sites and searching for new breeding areas over subsequent seasons is likely to provide more information on their breeding status.
The Antarctic Prion is by far the most populus species of burrowing petrel breeding on Macquarie Island. In the early 1980s their numbers were estimated to be around 49 000 breeding pairs. Monitoring of this species at permanently established transects was undertaken most years from the late 1980s through the 1990s. Following the eradication of feral cats from the Island monitoring showed an average increase of 11% (varied across plots, one had a decrease of 25%, the other two had increases of 48% and 38%) in burrow usage along the transects. This increase extrapolated across the total population suggested an overall increase of somewhere between 5,000 and 20,000 breeding pairs (Brothers 2000). Since this time little work has been done on this species so it is unknown whether this trend has continued. The population is still far from levels suggested by historical accounts of their abundance and distribution in the early 1900s (Falla 1937 cited in TSU 2004). Given many other burrowing petrel species on the Island appear to be impacted upon by the significant increase in European Rabbit (Oryctolagus cuniculus) and Skua numbers, it is highly likely that this species may also be affected.
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7.6 Recommendations
¾ Continue to search for signs of activity at known main island breeding locations for Fairy Prions (Rockhopper and Brother Point Caves) and Cape Petrels (Tip of North Head) over the summer breeding season.
¾ Continue to search for new breeding locations for Fairy Prions, Cape Petrels and Diving Petrel Species. Employ a combination of methods including spotlighting, night listening watches and ground searches early in the season to determine areas of high activity.
¾ Investigate the feasibility of visiting off shore stacks by boat to look for breeding activity over the summer. Visit known breeding locations first.
¾ Identify species of Diving Petrel visiting North Head. Look for birds roosting on the ground on North Head around Sept/Oct or bring birds down to the ground during spotlighting. Take measurements and photos for identification.
¾ Investigate appropriateness of repeating Antarctic Prion monitoring at previously established transects with the view to setting up long term monitoring to track trends in their population number, breeding effort and response to the eradication of feral pest species from Macquarie Island. Counts of active burrow were undertaken over a number of seasons in the 1980s and 1990s within established plots. Marked plots are located near Prion and Square lakes and results from some earlier counts are on file in the TASPAWS office on Macquarie Island. The survey seems feasible to replicate in December if other work commitments allow.
¾ Start mapping areas of high burrow density around the Island to assist with reserve management purposes. Take grid references from perimeter of dense colonies and locate colonies on a map of the Island.
64 8. Rockhopper Penguin (Eudyptes chrysocome) Monitoring
Photo: James Doube Photo: James Doube
8.1 Objectives of the 2006 season
3. Document base level data on the location and size of Rockhopper breeding colonies on Macquarie Island. 4. Investigate methods and establish a system for monitoring changes in the Islands Rockhopper breeding population over time.
8.2 Background
Rockhopper penguins (Eudyptes chrysocome), the smallest of the crested penguins, have a circumpolar distribution and breed on subantarctic and southern temperate islands in the Southern, Indian and Atlantic oceans (Marchant and Higgins 1990). There is disagreement about the taxonomy of Rockhopper penguins but most authorities recognise three subspecies that differ in morphological differences and geographical separation of breeding populations (Banks et. al. 2006). The eastern Rockhopper penguin subspecies, Eudyptes chrysocome filholi breeds on Macquarie and Heard Islands, the New Zealand subantarctic Islands, Marion Island and other islands in the southern Indian Ocean.
Rockhopper penguins are currently classified as vulnerable by the IUCN because of substantial decreases in populations at several breeding sites (Campbell Island, Tristan Da Cunha, Antipodes and Falkland Islands) over the last 30 years. If similar declines are detected in other larger colonies or if subspecies are recognised as full species (as suggested by Banks et al, 2006) their status, especially some subspecies, is likely to be upgraded to Endangered (The IUCN Red List 2007). In Australia the Rockhopper penguin is listed as a Marine Species under the Environment Protection and Biodiversity Conservation Act (1999)
Rockhopper penguins return to Macquarie Island over summer to breed and moult. Colonies are most often located in rugged rocky terrain which varies in complexity, steepness, exposure and amount of vegetated cover. In many situations they will nest on the more
65 rugged margins of colonies of the closely related, but larger and dominant, Royal Penguin. Colonies vary in size and make use of caves, rocky shorelines, space between and under boulders, steep rocky prominences, fissures and tussocky overhangs. In many west coast locations Rockhopper colonies abut denser Royal penguin colonies. Royal penguins mostly occupy the low flat terrain and Rockhoppers often occupy slopes at the edge or rockstack islands in the middle. The number of Rockhopper penguins breeding on the Island isn’t really known. Marchant and Higgins (1999) lists Macquarie Island’s population at 300 000 breeding pairs but this doesn’t appear to be based on any formal investigation. Difficulties accessing breeding locations and complicated terrain have meant little work has been done on this species. Warham (1963) suggested that it was not possible to estimate the Island’s total Rockhopper population but thought it was “likely to be in the order of some hundreds of thousands of birds”. Concerns for this species across its distribution, sparked by rapid declines at some breeding sites, prompts the need for an assessment of the current status of the Macquarie Island population.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rockhopper Colony amongst coastal Rockhopper nesting under Stacks tussock
The following information on the Rockhopper penguins at Macquarie Island was documented during field work conducted by John Warham between 1959-61. • Annual arrival and departure times are strongly correlated with sea surface- temperature (Warham 1972 cited in Marchant and Higgins 1990). • Breeding males generally return to Macquarie Island between the 18th of October and 1st of November, and females arrived up to two weeks later. • Non breeding immatures arrive gradually from the start of breeding season but most noticeably after the 5th of December. • Immatures and failed breeding birds will often roost at margins of colonies. • When birds come ashore they often rest and preen at sites close to landing places. • Adults leave colonies at the end of breeding around late Feb–early March, and return from late March to moult. • Non-breeding immatures leave gradually from breeding sites from January to February. • Most non or failed breeding birds moult in February.
Breeding in Rockhopper penguins is highly synchronous between individuals and well as over seasons (Hull et. al. 2004). Warham (1963) recorded the dates of various stages in the breeding cycle on Macquarie Island. Egg laying was recorded between the 7th and 18th of November with a peak between the 11 and the 16th. Two eggs were usually laid, an A and B egg which were laid 4-5 days apart. Incubation lasted for approximately 33-34 days and eggs generally hatched between 17th and 25th of December. The chicks were guarded by an adult for up to 3 weeks and then start crèching between the 6th and 16th of Jan. Chicks started fledging at approximately 10 weeks from hatching and generally left the Island from the 24th of February to the 10th of March. Both the A and B eggs can produce viable offspring but adults will only raise one chick to fledging. Only a small percentage of adults breed every
66 year. It is more common that pairs will breed once or twice every three years (Hull et. al. 2004).
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rockhopper Penguins on nests
Assessing the population during the breeding season ensures that the reproducing portion of the population is monitored, and follow up work can easily be repeated at the same time in future seasons. Eric Woehler and Nick Holmes (pers com) both suggested that the onset of the incubation period would be the most appropriate time to start monitoring the breeding population. At this stage one adult bird will be sitting tight on each nest and the number of non-breeding birds around the perimeter of the colony is likely to be at its lowest. Based on Warham’s (1963) research, most birds are likely to be incubating eggs after the 18th of November.
8.3 Methods
During the winter, prior to the return of Rockhopper penguins to Macquarie Island, much of the coastline was investigated for evidence (such as feathers, nest bowls, areas denuded of vegetation) of colony locations. This provided some insight into the distribution of breeding sites around the Island but this needed to be confirmed when the birds returned. Likely vantage points for viewing the colony were identified during this early visit. Past knowledge of colony locations and terrain assisted this process.
Once Rockhopper penguins had returned and were observed to be incubating eggs, coastal areas were again searched for breeding locations. Each discrete Rockhopper colony was given an identifying name usually corresponding to the Bay or Headland where it was located. Some colonies were split into sub-colonies when discreet nesting locations were found in the same area. For example the Green Gorge colony was split into Green Gorge A, B and C because it had three separate but closely located nesting areas. Along some sections of the coast, especially the west, it was not possible during this investigation to separate nesting areas into discrete colonies. Breeding sites in these areas often blended into Royal penguin colonies forming a complex mix of species with Royals generally occupying the low flatter ground and Rockhoppers located on the edges or on islands within where rougher terrain excluded the other species. These sections of the coastline were identified by the area they covered and included all nesting areas in that section. For example the Mid North Precarious Bay section contained numerous nesting areas in between Royal colonies, and the Mt Aurora section contained individual nests and small colonies between South Lusitania Bay and 4 Waterfalls Bay which were not individually identified.
When visiting colonies additional details such as the best approach route, type of terrain, date of visit, presence of Royal penguins and any other relevant information that would assist further monitoring was recorded. Any obvious shrinkage or extension of the colony boundaries was also noted.
67 Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Mixed Rockhopper and Royal penguin colonies
8.3.1 Monitoring Detecting change in the total breeding population on Macquarie Island over successive seasons may be achieved by monitoring changes at a colony level. Basic information on existing colonies can be collected and compared to the same data collected in future years. This season five options were trialled for future monitoring of Rockhopper Penguins.
8.3.1.1 Detecting change through population estimates Ideally, to monitor changes in the Rockhopper Penguin population on the Island, a census of all nesting birds at all colonies would be undertaken at the onset of the incubation period. However given the number of colonies and the complexity of the terrain, combined with difficulties of access and disturbance to the colonies and other species, this option was not a possibility. Alternatively, other researchers (such as Cunningham and Moors (1994) and Bingham (1998) on Campbell and the Falkland Islands), on encountering similar obstacles, estimated the size of Rockhopper Penguin populations by using total area occupied and nest density figures. The accuracy of this kind of estimation is dependant on accurate mapping of colony boundaries and consistency of nest density estimates across the colony. The extremely varied terrain exhibited within and across colonies on Macquarie Island makes an estimation of an accurate nest density figure quite difficult. Calculating a usable nest density would require the calculation of a series of density figures to be applied to different types of terrain such as coastal stacks, caves, thick tussock or cabbage covered slopes, coastal rock and boulder fields. Each terrain type would need to be mapped accurately to calculated areas for density figures to be applied to. Time and resource constraints over the 2006/7 season meant this type of approach was unsuitable.
Total nest counts were thought to be a feasible monitoring tool at some individual Rockhopper colonies around the island. Counts were undertaken at small (below 300 nests), easily accessible and non-cryptic colonies where activities wouldn’t greatly disturb the colony or other species. Counts were undertaken between the 21st of November to the 18th of December when birds were incubating eggs or guarding chicks. Nests were counted from vantage points around the edge of colonies. Mud maps were often drawn to document nest location to avoid double counting from different vantage points. All birds sitting tight on nests were counted so it is possible that some non-incubating birds (practicing non-breeders) were included in the counts. The area surrounding colonies was searched for outlying nests or signs of nesting activity indicating the presence of other nesting areas (such as faeces or tracks). Abandoned nests were recorded and listed separately when observed.
At larger more complex and cryptic colonies an attempt was made to provide a rough estimate of the number of nests in the colony. At some colonies estimates were achieved through rapid nest counts from observation points around the periphery of the colony and at others very rough estimates were achieved by considering the area occupied by the colony, and based on counts from other colonies, estimating the number of nests likely to occur in the area. An estimation of the margin of error was also given (e.g.+/-100). Estimates were awarded a ranking of accuracy base on the observer’s confidence in the estimation. Estimations were
68 described as: rough estimate, very rough estimate and extremely rough estimate and this was noted in the census spreadsheet with the figures.
8.3.1.2 Detecting change through photomonitoring points. Repeated photos of penguin colonies over time have been used by researchers (Cunningham and Moors 1994) to document population declines in the Rockhopper Penguin population on Campbell Island. In this example shrinkage of the area occupied by penguin colonies was detected when historic photos were compared to more recent images. Photos of colonies taken from the same point over time could be used to monitor changes in colony extent and density. If the number of breeding birds at a colony starts to decline then the size and or the density of nests will decrease. Conversely, if the number of breeding birds increases, the colony may start to expand beyond its current boundary (or increase density or form new colonies). If changes in colony size are detected in numerous colonies then it is likely that the trend is occurring across the total breeding population.
During the 2006/7 breeding season an attempt was made to establish photomonitoring points at as many Rockhopper penguin colonies around the Island as possible. Few vantage points provided good views of complete colonies so often only sections could be photographed. The majority of colonies were visited from the 21st of November to the 18th of December when adult birds were incubating eggs or guarding chicks. Photos were taken from vantage points that offered the best view of most of the colony. Often a series of overlapping photos were taken to provide better coverage. In most instances more than one vantage point was used to photograph different sections of the colony. Where terrain prevented complete coverage, partial colony photos focussed on colony margins. Where possible these photos included permanent features such as rock outcrops and crevices so comparisons over time can be easily made. At many colonies the nature of the terrain and/or vegetation cover obscured nest sites making these colonies unsuited to photomonitoring. Site photos were still taken these colonies to assist in their relocation in future years.
The majority of photos were taken with a compact digital camera (Pentax Otio WPi). Photos of colonies in the south west of the Island were taken with a Nikon D80 digital SLR camera system. Photos were stored digitally in folders on the TASPAWs computer system on the Island. Focal lengths and resolution are recorded in Exif data. Photos were labelled with the Colony name; photo point number and photo letter (eg Saddle Point A PhPt1A). Grid references were recorded for most Photopoints to assist relocation in future years.
8.3.1.3 Detecting change through colony mapping Mapping Colony Location Recording and mapping the location of all Rockhopper colonies around the Island will provide some base line information to compare with future years. Over time some colonies may disappear or new colonies may be established. During the 2006/7 summer most of the coastline of the Island was searched for nesting Rockhopper penguins or signs of their presence. This was mostly done by foot but inflatable boats were used on some occasions. All searching was conducted from November to February. Notes describing the location of the colony were recorded along with an estimation of its size.
Colony Perimeter Mapping Recording multiple perimeter points around the area occupied by nesting birds using a hand held GPS and GIS software enables the colony to be plotted onto a map. The area occupied by nesting birds can then be calculated and compared to subsequent perimeter mapping of the colonies to detect change in colony size over time.
Where possible, points around the perimeter of colonies were recorded using a hand held Garmen etrex GPS. Mapping was only undertaken when the GPS showed an error reading of below 15m. Points were generally recorded every 10 – 20 meters (more frequently in rough
69 terrain) while moving around the edge of the colony. The perimeter was walked at greater than 5 meters from the edge of nesting birds but an attempt was made to mark points at less than that distance. Points were marked as close to the edge of the colony as possible (generally within 1 metre) by approaching low to the ground or from behind vegetation or rocks. Mapping was undertaken between the 21st of November and 18th of December when birds were incubating eggs or guarding chicks. When access prevented the full perimeter being mapped, edges or a few points marking the Nth/Sth, East/West extent of the colony were recorded. Along some sections of the coastline Rockhopper Colony distribution was too complex to map due to terrain and overlap with Royal Penguin colonies. In these areas pockets of nesting Rockhoppers were sometimes marked or nesting was just noted to occur between broad grid reference points. For example along sections of the coast, identified in the North Precarious Bays, Rockhopper activity was not mapped but the whole stretch was identified as possibly having breeding sties.
As waypoints were recorded on the GPS notes were taken to assist with later interpretation of the data (for example details on which side of the colony and the start of gaps in edge due to Royal colonies, rock stacks, etc).
All mapping data was later stored in an excel spreadsheet and loaded into Arcview 3.2 GIS software for mapping.
8.3.1.4 Breeding success
Follow up visits were made to some colonies, where nest had been counted, to conduct a count of creching chicks. Counts were undertaken in early February before chicks became fully feathered and difficult to distinguish from adults. Other work commitments at this time prevented many chick counts being undertaken.
Photo: Helen Achurch Photo: Helen Achurch Photo: Helen Achurch
Rockhopper penguin chicks at crèche age
8.4 Results
Forty six Rockhopper Penguin colonies or sections of coast containing nesting birds were identified during the 2006/7 season. For the purposes of mapping, photographing and nest counting some colonies were split further into sub colonies where distinct gaps were noted within the main colony. In total sixty six colonies or sub colonies were identified and listed in the census spreadsheet. Most colonies were visited during the season and notes on their location, date of visit, access and approximate size were recorded and photos taken. The 2006/7 Rockhopper Penguin Report contains these details.
Accurate total nest counts were conducted at 22 of the smaller colonies or sub-colonies. For the purposes of comparing colony sizes around the Island, very rough estimates of nest numbers were made at the bigger colonies and sections of the coast. When total nest counts
70 and rough estimates for the whole Island were tallied this figure came to between 32 000 and 43 000. This figure applies to breeding pairs and it should be remembered that actual breeding population would be a lot larger than this given pairs are likely to only breed once or twice in three years (Hull et. al. 2004). Given the cryptic nature of this species, complicated terrain and feasibility of colony estimations, the overall amount is likely vary significantly from the figure given. Results from colony counts and estimations are contained in the 2006/7 Rockhopper Penguin Report.
A few areas of the coastline that were difficult or impossible to access by foot, nor able to be safely viewed from above, such as between Windsor Bay and Hurd Point Beach, and Tottan Head, were only observed from boats. Additionally, Star Bay was not entered, but observed from the escarpment and from boats. Furthermore the section of west coast from the station to Aurora point (the “Featherbed”) was searched for signs during winter, but not thoroughly searched during the breeding season due to time constraints (and lack of sign or known colonies).
The 2006/7 Rockhopper Penguin Report contains a list of colonies and the location of photo points at each. Grid references were not collected at all points due to problems with GPS accuracy or other problems. One hundred and twenty photo points were established at vantage points around Rockhopper colonies and photos or a series of photos were taken from each point. The suitability of the photo points and photos was noted in the census spreadsheet.
Figures 8.1, 8.2 and 8.3 show the approximate location of most Rockhopper Penguin colonies around the Island. They also indicate coastal areas which are likely to contain other colonies, but could not be properly surveyed when visited this season.
Grid reference points around the complete perimeter of nesting areas were only collected at a few colonies. In most cases access restrictions meant that only parts of the perimeter could be mapped and in some cases only a few reference points to document the colonies extent were collected. It was not possible to calculate the area covered by colonies using perimeter mapping before writing this report but, this is likely to be undertaken in the future when access to appropriate GIS software is sorted out. All perimeter points marked around colonies are recorded in a spread sheet kept on file in the TASPAWS office on the Island.
The first hatched chicks were heard or observed at colonies on the 17th of December. Due to other work commitments only 10 colonies were revisited in early Feb for a count of chicks prior to fledging. Results are contained in Table 1 below.
Breeding Colony Sub colonies Nest Count Chick count Success (%) Rockhopper Rockhopper Cave Cave East East 14 24 N/A Ham Shack Hill Ham Shack Hill A 148-153 115 77 Ham Shack Hill B 6 3 50 Green Gorge Green Gorge A 70-75 54-57 77 Green Gorge B 16 16 100 Green Gorge C 9 4 44 Saddle Point Saddle Point A 37 23 62 Saddle Point B 32 19 59 Saddle Point C 30 12 40 Saddle Point D 13 6 46 Total 62 Table 8.1 – Breeding success at ten small Rockhopper Penguin Colonies over the 2006/7 season.
71
Figure 8.1 Approximate location of Rockhopper penguin colonies around Macquarie Island – Northern 1/3
72
Figure 8.2 Approximate location of Rockhopper penguin colonies around Macquarie Island – Central 1/3
73
Figure 8.3 Approximate location of Rockhopper penguin colonies around Macquarie Island – Southern 1/3
74 8.5 Discussion
Over the 2006/7 season baseline data was collected on the Rockhopper population breeding on Macquarie Island and some long term monitoring options for this species were trialled and initiated. The time and resources available for this investigation were limited and the outcomes, although very useful, reflect these limitations. Further work over subsequent years can build on, and improve, the current data set. A number of monitoring options were trialled at colonies around the Island including: colony location mapping, total nest counts, photo monitoring, colony perimeter mapping and breeding success. Monitoring options varied in their suitability and were greatly dependent on features presented at individual colonies. i.e. some options were suited to some individual colonies and not to others. This is discussed in greater detail below. Results tend to indicate that an effective long term monitoring system should incorporate a combination of options at a mixture of colonies. The greater the monitoring effort, the greater the likelihood that changes in the overall Rockhopper penguin population will be detected.
8.5.1 Colony Location Mapping Figures 1 to 3 record the results of the 2006/7 census and document the rough location of most Rockhopper colonies around the Island. This is the first time Rockhopper colonies on Macquarie Island have been mapped in this detail. Colonies varied greatly in size with some containing as little as ten nests while others contained up to 2000. It is highly likely that some small colonies were overlooked during this investigation, especially in areas that weren’t actively searched such as: between the eastern extent of Windsor Bay and Hurd Point beach; Carrick Bay; and Star Bay. The escarpment slope and coastline between Lusitania Bay and Mt Jeffryes had a number of small colonies which were only detected when birds were heard or seen on nests and travelling to and from colonies. A thorough search of this area is likely to locate more of these small groups of nesting birds. In early November Rockhopper penguins were heard in the vicinity of Mawson Point but searches along the coastline failed to locate them. The coastline between Cape Toutcher and Cape Star contained a continuous spread of Rockhopper and Royal Colonies. Royal penguin colonies were denser and covered the majority of the area. The location of Royal and Rockhopper colonies appeared to be dictated by terrain, with Royals in flat easily accessed areas and Rockhoppers in rocky boulder fields along the coastal margin, up steep escarpment slopes and on coastal stacks. The two species often shared mutual colony boundaries and in some instances nest sites were intermingled at the margins. The identification of individual Rockhopper colonies in these areas was not possible during this investigation.
Photo: Helen Achurch Photo: Helen Achurch Photo: James Doube
Royals passing through a Rockhopper colony. Curious Rockhoppers
Given penguins often return to the same colonies to breed, the distribution of colonies around the Island (aside from the areas of uncertainty) could be used as a course indicator of change in the total number of breeding birds nesting on Macquarie Island. i.e. The discovery of additional colonies over time may indicate an expansion of the total population and
75 conversely the loss of known colonies could indicate a decrease in the overall population. Checks on known colonies and searches for new colonies should be undertaken over subsequent seasons. If many changes are noted then this should trigger the need further investigations.
In the complex mixed colonies it may be possible to take photos of the colony with nesting Royals before the Rockhoppers arrive (they are separated by nearly a month), and compare these with identical photos taken a month later. However, in practice the interpretation of these photos may prove difficult as the boundaries between species are often blurred, and the separation of the species on a photo can be problematic if the head is obscured or the distance great.
8.5.2 Total nest counts Total nest counts were undertaken at most of the smaller accessible colonies around the Island. Often individual nests or small numbers of birds were located away from the main groups. These outlying nest sites were often hidden under boulders, in crevices or upslope amongst vegetation. Nests were often found by tracks in the mud, faeces near the nest and by birds calling. It is extremely easy to miss nests and therefore undercount. It was obvious that a small group of nests were missed at the Rockhopper Cave East site when the number of chicks was found to exceed the original nest number. In future the chance of this error occurring could be reduced by spending a greater amount of time searching around the colony and watching where birds return or leave from. In some cases, especially in bouldery areas, it is impossible to see all nests, but this is likely to be the case in subsequent years as well.
Accurate total nest counts were achieved at twenty-two out of the sixty-six identified colonies and sub-colonies (see 2006/7 Rockhopper Penguin Report). Nest counts at these colonies can be easily repeated over subsequent season, especially now that their extent has been documented by grid reference points. Comparison of nest numbers at these small colonies and sub colonies over time could be used as an indicator of change in the overall Rockhopper population on the Island. Although it is unknown whether changes in the population will first impact upon small or large colonies, it is likely that changes will be easier to detect in smaller, distinct, colonies. Increases and losses from these small colonies could then trigger further investigations at larger colonies. To improve understanding of the natural variation in colony size at these smaller colonies nest counts could initially be undertaken over a number of successive years before decreasing to every few years for long term monitoring.
8.5.3 Population estimate For the purpose of arriving at a ball park figure for the number of breeding pairs on the Island this season and for comparing the relative size of colonies around the Island, a very rough estimate of Rockhopper nest numbers was provided for the bigger colonies and sections of the coast. A tally of these estimates and the total nest counts at the smaller colonies came to 32000 to 43000. This figure relates to breeding pairs this season and it should be remembered that the actual breeding population would be a lot larger than this given pairs are likely to only breed once or twice in three years (Hull et. al. 2004). The cryptic nature of this species, complicated terrain and feasibility of colony estimations suggest that the total number of breeding pairs is possibly larger the above range. This figure is unsuited to comparisons with future estimations as it is very subjective and vulnerable to observer error. The accuracy of this estimation could be improved upon by revisiting the colonies were the more marginal estimations were made (Especially if time was taken to develop an improved method for making estimations).
76 Photo: Helen Achurch Photo: Helen Achurch
Mt Jeffryes Rockhopper Penguin Colony
8.5.4 Photomonitoring This method of monitoring assumes that decreases in the total Rockhopper population will be reflected at individual colonies through declines in the number of breeding birds returning to the colony to breed. With a decline in nest numbers, at least some colonies will either shrink back from their current perimeters, as remaining birds seek better nest sites, or the density of nest sites across the colony will decline.
One hundred and twenty photo points were established at vantage points around Rockhopper colonies and photos or a series of photos were taken from each point. Photo points varied in suitability for future monitoring and photos varied in quality. Photo points were more suitable if they showed the complete colony or large areas of a colony including margins. Suitability of the photo points was recorded on the census spreadsheet. At some colonies no vantage points offered an adequate view of the colony and these were deemed unsuited to photomonitoring. In subsequent seasons photos can be taken from photo points, at the same time of the season, and at some point (unknown at this stage) changes in colony extent or density should be detected. If this trend is noted at numerous monitored colonies then changes may be indicative declines or increases in the total Rockhopper population. Similar to the total nest counts, photomonitoring should be undertaken over a series of years to get a feel for natural variation in the density and extent of nests at the colony. If colony densities starts to decline or margins start to shrink away from the colony perimeter over subsequent years, further investigations into the change should be instigated.
Some improvement could be made to the current collection of Photomonitoring data. Some photos were taken from good vantage points but were taken late in the 2006/7 season. At this time the number of non breeding birds around the edges confuses the location of perimeter nest sites. Photos at these colonies should be retaken earlier in the season (between the 18th of November and 5th of December) before non breeding birds turn up at the colonies.
Photo quality is a factor affecting the suitability of photomonitoring photos. The resolution and quality of photos from photo points is sometimes not adequate for clearly distinguishing the perimeter of the colony. This can also be a problem when distinguishing between Royals and Rockhopper penguins when colonies are mixed. These photos need to be either retaken with a better camera (probably an SLR with an appropriate lens) or a closer photo point needs to be established. It must be noted that although a cheap compact camera may have a similar number of pixels as a higher quality SLR, the quality of the image can be vastly different. Photos taken from the water may also be affected by mist, but in many cases this is outweighed by the close approach possible and appropriate aspect.
77 Photo: Helen Achurch Photo: Helen Achurch
4 Waterfalls Bay Colony photographed from off shore
8.5.4 Colony Perimeter Mapping This method is likely to be the least effective of the monitoring options trailed this season because of access to the colony edges, the type of GPS being used and GIS software limitations. The complete perimeter of very few colonies could be mapped due to obstacles such as Royal colonies, rock walls and drop-offs. At other colonies only some edges could be accessed so perimeter points were recorded along these. At some colonies points were only recorded at their south/north, east/west extent. Colony perimeter points were loaded onto a basic copy of Arcview 3.2 GIS software for display. Colony areas were not calculated prior to writing this report. It was thought that the perimeter of colonies or sections of colonies could be remapped in subsequent years to document shrinkage or expansion over time or colony areas could be calculated and compared over time. The accuracy of the GPS used during to collect of perimeter points this season was of a standard that would have only picked up very coarse changes in colony boundaries over time. It took a considerable amount of effort to collect the perimeter points and their effectiveness as an option for monitoring colony change at this accuracy is questionable. However, the points were useful for documenting the location of colonies. This monitoring method could be vastly improved by the use of a differential GPS which would provide much more accurate locations (sub-metre accuracy would be sufficient).
8.5.5 Perimeter observations The majority of colonies appeared to be full and densely populated this season. A small amount of nest area shrinkage was detected at only three Rockhopper colonies. At these colonies there were vacant nest bowls and denuded areas of vegetation along some sections of the perimeter but this was never very extensive. Observed shrinkage of nest areas at a number of colonies would indicate that their extent had changed from the previous year which may could trigger some further investigations. Observed shrinkage is unlikely to be a good way of monitoring change over a longer time without the use of reference photos.
8.5.6 Breeding Success Monitoring breeding success at some colonies will give information on the status of the Island’s total population, and may also provide more detailed information on the population ecology. Generalised increases in nest failures may be indicative of problems affecting the total population of Rockhopper penguins (e.g. prey availability), whereas isolated changes may reflect local effects (such as intraspecific site competition, predation or disturbance). Birds may still return to colonies to breed but may fail partway through the season. This will not be detected as rapidly by other monitoring methods. Chick counts were undertaken at 10 small colonies this season and results are listed in table 1 above. An average breeding success of 62% (number of chicks as a proportion of the number of birds on nests) was calculated but a number of limitations to this result must be considered. Firstly chick counts were done at only a few colonies so the sample size was very small. Colonies were only visited twice, once
78 to count nests and once to count chicks prior to fledging so nests or chicks may have been missed. This would significantly affect breeding success calculations in a small group. Nest counts did not confirm that birds were sitting on eggs so this number may be inaccurate. Chicks were only counted at small colonies and breeding success may vary significantly between these and larger colonies (due to factors such as edge effects and the large mixed colonies may have significant intraspecific competition). However, monitoring breeding success is a feasible method for monitoring the status of Rockhopper penguins, and could be improved if greater effort was put into collecting the data. Small colonies and sections of some larger colonies could be monitored during successive breeding season to detect changes in breeding success. An area in large colonies could be marked out before birds return and observations could be made using binoculars. An increase in the number of visits through the season would help to determine whether birds were incubating eggs, and improve the chances of all nests and chicks being counted.
Each monitoring technique trialled this season had varied levels of success depending on individual colonies. Each colony was awarded a priority score from 1 to 4 for its suitability for ongoing monitoring and the most appropriate method to use. Higher priority colonies were suited to continued monitoring based on ease of conducting the monitoring methods and accessibility. Using this suitability ranking a subset of representative colonies could be selected for inclusion in a future monitoring system. Obviously the more data collected, the greater the accuracy of information to work from in future years.
Photo: Helen Achurch Photo: Helen Achurch
Mapping the perimeter of the North Double Point Colony
8.6 Recommendations
¾ Work through the suggested improvements to the current data set, listed against each Colony in the Census spreadsheet (Includes suggestions such as: obtain reference points for the northern boundary of this colony or retake photos from a closer monitoring point etc).
¾ Where estimations of penguin numbers, at colonies or along sections of the coast, are noted to be (1) very rough or (2) extremely rough, revisit these sites and attempt to provide a more accurate count. Estimations could be dramatically improved on by spending more time at each site counting nest numbers from good vantage points with binoculars.
79 ¾ Compare the current data set with anecdotal accounts or historic photos of Rockhopper penguin distribution around the island and colony size. Contact previous rangers and researchers (such as John Warham or Cindy Hull) who may have photographs of Rockhopper Penguin colonies or other historical information. Also search iMAGE Antarctica (through AADC) and digitally accessible parts of National Achives for historical images. Through this process some insight may be gained into whether the population has expanded or contracted over recent times.
¾ Continue to search for new Rockhopper colonies. Priority areas include the coast along the southern end of the Island (Windsor Bay to HP), from Aurora Point to Bauer Bay, from Waterfall Bay to Hurd Point and in Star Bay. A boating trip along the southern end of the Island may determine whether colonies exist along this section of the coastline. Searching for colonies would be best conducted after the 5th of December when non breeding birds return to colonies making identification of breeding locations easier.
¾ Recount nesting birds at colonies where total nest counts were undertaken in the 2006 season. These colonies are indicated in the Census table. Repeat counts could initially be done yearly to determine the natural variation in their size and then recounts could be done every few years to note changes colony attendance and use these results as an indicator of trends in the total breeding population.
¾ Photomonitoring: (1) Retake photomonitoring photos from points at nominated colonies. (2) Some photos were taken from good vantage points but were taken late in the 2006/7 season which may cause confusion in identification of boundaries due to the presence of non breeding birds at the edges. Retake photos from these points between the 18th of November and 5th of December before large numbers of non- breeding birds arrive at the colonies. (3) Review photos of other colonies and where possible search for more suitable photomonitoring points. If photos of the whole colony are not possible, target edges where recession and expansion of the boundary are likely to be noted. If colonies contain a mixture of Royals and Rockhopper penguins then photo resolution must allow them to be distinguished. Replace original photo point details in the spreadsheets and exchange photomonitoring photos.
¾ Replot colony boundaries and extents using a differential GPS.
¾ Continue to collect breeding success information at nest counted colonies. As mentioned above counts could initially be done yearly to evaluate natural variation and then breeding success could be monitored over time and used as an indicator of trends in the total breeding population
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