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.