Australian Field Ornithology 2019, 36, 47–55 http://dx.doi.org/10.20938/afo36047055

Are Kelp dominicanus replacing Pacific GullsL. pacificus in ?

William C. Wakefield1, 2, Els Wakefield2 and David A. Ratkowsky3*

1Deceased 212 Alt-na-Craig Avenue, Mount Stuart TAS 7000, 3Tasmanian Institute of Agriculture, University of Tasmania, Private Bag 98, Hobart TAS 7001, Australia *Corresponding author. Email: [email protected]

Abstract. The nominate of the Pacific Larus pacificus, widespread along the coast of southern Australia, may be under threat from the slightly smaller, but opportunistically competitive, self-introduced L. dominicanus. To assess this threat to the Pacific Gull in Tasmania, we documented colony size of large gulls across many Tasmanian islands over a period of 24 breeding seasons (1985–2009). The most northerly Kelp Gull nests on the Tasmanian mainland were located at Paddys Island, St Helens. There were no reports of Kelp Gulls along any part of the northern coast of Tasmania abutting , although there were sporadic sightings on islands of the . The stronghold of the Kelp Gull in Tasmania is the Estuary of the Derwent River and its surrounding bays and channels, where this is present in much larger numbers than the Pacific Gull, but nevertheless co-exists with that species. We found no evidence for dramatic changes in numbers since 1985. All Pacific Gull nests were on small islands, and there were none at , which became the third biggest Kelp Gull colony studied in the south-east of Tasmania. At the largest Kelp Gull colony (), the number of Pacific Gull nests declined while numbers of Kelp Gull nests increased, but no such inverse correlation wasobserved elsewhere, including Curlew and Hog Islands, where numbers of Kelp Gull nests increased. We conclude that numbers of Pacific Gulls have remained reasonably stable, despite increases in Kelp Gull nests at certain sites.

Background to the study (Serventy et al. 1971), occurring mostly along the coasts of southern Australia (Higgins & Davies 1996; Menkhorst et The late Dr William Charles (Bill) Wakefield (WCW), a al. 2017). The Kelp Gull is believed to have self-introduced medical practitioner with a lifelong interest in avifauna, (i.e. colonised) (Serventy et al. 1971), the first published had more than 50 years of experience in research on sightings in Australia having been made at Botany Bay, New seabirds and land , and handled and banded at least South Wales, in January and February 1943 (McGill 1943), 100 000 birds in Australia and the United Kingdom. In though two earlier records were recognised subsequently the Australian and Bat Banding Scheme, he was an (Higgins & Davies 1996): at Claremont, , A-class bander with experience in all forms of capture of in August 1924 (Ford 1965); and Port Stephens, New birds from a broad range of species. With his wife Cherry, South Wales, in January 1938 (D’Ombrain 1973). After an he moved to Tasmania from the United Kingdom in 1972 expansion in its range in the 1960s, it established breeding and investigated gulls there from c. 1974. His wife and populations in New South Wales, Victoria and Tasmania, three sons accompanied him on visits to refuse tips to and its range expanded into South Australia and the count gulls and checked the beaches where Pacific Gulls southern coast of Western Australia (Close 1981; Warneke Larus pacificus fed during winter. After Bill and Cherry & Dann 2013; Menkhorst et al. 2017). It became numerous divorced in 1985, Bill met and married Margaret (Maggie), in south-eastern Tasmania but remains scarce elsewhere who, until she became ill in 1999, often accompanied him and, like the Pacific Gull, is largely absent from northern to the islands and assisted with the banding of chicks Australia (Higgins & Davies 1996; Menkhorst et al. 2017). and counting of nests. Beginning in January 1985, in In addition to having a similar geographical distribution in addition to the bird-banding activities, Bill undertook Australia, the two species are similar in morphology and several scientific projects concurrently, two of them being there is a considerable overlap in their diets (Coulson & ‘Trends in breeding bird population sizes’ and ‘Interactions Coulson 1993). However, there is a major difference in between populations of gulls and terns’. During Maggie’s their world-wide distribution. Whereas the Pacific Gull is illness, Bill had to abandon his banding and counting confined to the coasts of southern Australia, the Kelp Gull activities between the breeding seasons 1999–2000 and is widely distributed in the Southern Hemisphere, with 2002–2003. Counting resumed in October 2003 with the large breeding populations in South Africa (Whittington et assistance of Els Hayward (later Els Wakefield, EW) and al. 2016), South America (Yorio et al. 1998), New Zealand continued until the end of breeding in 2009–2010. He died (Fordham 1967), many sub-Antarctic islands (Sibley & in 2011. Monroe 1990), and the Antarctic Peninsula (Watson 1975; Quintana & Travaini 2000; Branco et al. 2009). Most Introduction populations are coastal but the species ranges far inland in Patagonia and New Zealand (Burger & Gochfeld 1996). Tasmania has two species of large gull, the Pacific The first documented sighting of the Kelp Gull in Gull Larus pacificus Latham, 1801 and the Kelp Gull Tasmania occurred in 1955 at Ralphs Bay (Wall 1956). L. dominicanus Lichtenstein, 1823. Historically, only Less than a decade later, in 1963, the first breeding record the former was present in Australia, where it is endemic was reported at Curlew Island (Wolfe 1969) (see Table 1 48 Australian Field Ornithology W.C. Wakefieldet al.

for the latitude and longitude of this and other Tasmanian extent that these gulls were preventing adult Pacific Gulls localities), and within a few more years the Kelp Gull from holding territories during winter, possibly influencing had established a considerable stronghold in Pitt Water survival or reproductive success of that species. Coulson (Thomas 1967), where it was reported in all seasons of & Coulson (1998) suggested that control of the Kelp Gull the year. population might be warranted if there were evidence of further detrimental effects. They concluded that more study Before 1985, the only information about nesting was needed to determine whether the population increase and the diets of the Pacific and Kelp Gulls in Tasmania of the Kelp Gull might influence the survival or reproductive was obtained from a study between 6 November and success of the Pacific Gull. 5 December 1981 on Green Island, where both species were known to breed. Examination of 43 regurgitated pellets Here we report on colony size (a likely correlate of from 27 Pacific Gull nests and 44 regurgitated pellets from reproductive output) of these two species of large gull 275 Kelp Gull nests revealed that both species utilised a resident in Tasmania obtained over a period of 24 breeding wide range of food sources (Coulson & Coulson 1993). seasons from 1985 to 2009, for 22 Tasmanian off-shore For the Pacific Gull, the most frequent food categories islands and one land-based vantage point. We use these were crabs (Crustaceae: Decapoda), fish, and chitons data to address the question of whether the population of (Mollusca), and many pellets contained food remains one of these species is increasing to the detriment of the from more than one of these sources. Refuse was rare in other species. these pellets. In contrast, the most frequent component in the Kelp Gull pellets was refuse (including glass, string, Methods plastic, paper, aluminium foil and chop bones), although remains of chitons and fish were also quite common. From Study site localities surveys of large refuse tips and specific shoreline sites during winter in 1981 and 1992, recording numbers and The various surveys did not cover the whole of Tasmania, age classes of each species, Coulson & Coulson (1983, and no attempt was made to cover the major coastal regions 1998) found that Kelp Gulls of all ages were far more of the state. Because of close proximity, the Derwent abundant at refuse-disposal sites, whereas adult Pacific River and its Estuary, and many of the numerous islands Gulls fed preferentially at more natural shoreline sites. in its various bays and channels, were a particular focus. During the 11-year gap between the two surveys, the These included, but were not limited to, , Barren, Kelp Gull in south-eastern Tasmania had increased to the Betsey, Curlew, Fulham, Green and Hog Islands, ,

Figure 1. Map of Tasmania showing the locations that were visited in this survey. Names of closely overlapping sites are not shown. The full list follows: E – Governor I., Lachlan I., Visscher I.; NE – Paddys I.; NW – Howie I.; SE – Derwent River Estuary: Betsey I., Iron Pot; D’Entrecasteaux Channel: Arch Rock, Charity I., Curlew I., Garden I., Green I., Huon I.; : Hog I., Isle of Caves, Slopen I., Spectacle I.; Pitt Water: Barren I., Orielton Lagoon, Susie Islet; : Fulham I., King George I., Smooth I. See Table 1 for the latitudes and longitudes of these localities. I. = Island; E = east, NE = north-east, NW = north-west, SE = south-west. Are Kelp Gulls replacing Pacific Gulls in Tasmania? 49

King George, Smooth and Spectacle Islands, and Susie islands where both species bred, the nests were sometimes Islet (see Table 1). Many of the islands were already known intermingled, and sometimes quite close together. In to be important breeding places for one or both species. general, Pacific Gull nests were tidier, higher-walled and There were no visits to the southern coast, the south-west, larger than Kelp Gull nests, which were messier and lower- or the north-western coast south of Cape Grim. However, walled, making it possible to identify them even before islands along the eastern coast were visited (Governor, laying had commenced. Kelp Gulls seemed to be more Lachlan and Visscher Islands), as were parts of the opportunistic than Pacific Gulls in their nesting behaviour, north-east (Paddys Island) and north-west (Howie Island) as demonstrated, for example, by a large Kelp Gull colony (Table 1). Not all of the targeted areas were islands, as at the northern end of Orielton Lagoon where the nests in one instance (the northern end of Orielton Lagoon were occasionally flooded by high tides, and the eggs near Frogmore Creek), observations were made on land. often submerged by water or covered in mud, resulting in All sites were in locations where there was little human mortalities. No Pacific Gulls were recorded breeding at this interference or activity that would discourage the birds site. from nesting.

Numbers of Kelp Gull and Pacific Gull nests Number of nests Kelp and Pacific Gull nests were documented at 23 sites in Visits to the various localities were made on an ad hoc Tasmania over the 24 breeding seasons from 1985 to 2009 basis, not following any rigorous sampling program. For (Table 1). Survey effort at individual sites ranged from 2 to the purposes of this survey, nest numbers alone are used 17 breeding seasons. Most Kelp Gull colonies contained as the measure of breeding effort. Numbers of nests of all <100 nests in a breeding season, four colonies contained bird species were counted during each visit. Records were 100–200 nests, and one colony (on Green Island) contained made of the number of eggs present and whether the eggs an average of 483 nests. Pacific Gull colonies mostly were cracked or if hatching had previously taken place and contained <10 nests, though three colonies contained whether live or dead chicks were present. Although every 10–30 nests, and two colonies contained >100 nests effort was made to record the nests of every bird species (Table 1). The 23 study sites were divided into two groups at each visit, the onset of inclement weather sometimes for the purposes of this presentation. One group of five sites curtailed observations. Also, the larger islands (e.g. Betsey had each been visited during at least 10 breeding seasons. Island, with an area of 176 ha) had active nests located in At four of these five sites, statistically significant regression more than one place, and it cannot be guaranteed that all relationships (P <0.05) were obtained for at least one of the nesting areas were observed. two gull species. The second group, comprising 18 sites, had each been visited between two and nine times and usually showed non-significant regression relationships. Statistical and graphical methods At Green Island, whilst there was an upward trend in number of Kelp Gull nests the slope did not differ significantly The main questions of interest were whether there has from zero (Figure 2). From the fitted regression line, the been a change in numbers for either species and to what predicted average number of nests increased from 421 in extent the numbers of one species might influence those 1985–1990 to 611 nests in 2003–2008. During the same of the other species. For this purpose, we employed time periods, Pacific Gull nests on Green Island declined regression analysis to determine whether there were significantly from an average of 16 nests to just one nest statistically significant trends in the data for each breeding (P <0.05). At Barren Island, there was a highly significant site as a function of time. Simple linear regression upward trend in number of Kelp Gull nests throughout proved to be adequate for almost all data sets, although the observation period spanning 22 breeding seasons, polynomial regression was used when visual inspection of 1988–2009 (P <0.001: Figure 3). During the same time the response curve indicated that it was curvilinear. period, only one Pacific Gull nest was observed, and In all the figures in this paper, ‘breeding year’ indicates that in only one of the breeding seasons. At Curlew the year of the start of the breeding season (e.g. 1985 Island, there was a highly significant (P <0.001) upward indicates the 1985–1986 breeding season). trend in the number of Kelp Gull nests during the 23-year observation period, the number increasing from a few nests before 1989 to an average of 23 nests in 2000–2007 Results (Figure 4). This contrasts dramatically with the number of Pacific Gull nests, which remained largely constant, with Habitat preferences of the two gull species an average of 25.6 nests during the observation period. We note, however, that the Pacific Gull nests, on average, Pacific Gulls nested only on islands and always placed outnumbered the Kelp Gull nests at this site, this being their nests well above high-water mark, in areas sheltered one of the few islands surveyed where this occurred. At from prevailing winds and on corners, cliffs and raised , there was a slight upward trend in number areas around the edges of the islands, with good views of Kelp Gull nests, but the slope of the regression line of approaching predators and proximity to good hiding did not differ significantly from zero (P = 0.560: Figure places between the rocks for chicks. Pacific Gulls nested 5). Similarly, there was also a slight upward but non- in similar locations every season, being faithful to previous significant trend in number of Pacific Gull nests (P = 0.136: nest-sites. On some islands, Pacific Gulls nested as a Figure 5). There was, however, a big difference between the small colony and on others single pairs had isolated nests average number of nests of the two species (Kelp Gull 174 at various spots around the edge of the islands. On the vs Pacific Gull 18) during the 23-year observation period 50 Australian Field Ornithology W.C. Wakefieldet al.

Table 1. Average number of nests of the Kelp Gull and Pacific Gull in Tasmania during the breeding seasons in 1985–2009. Localities shown are those that were visited in at least two breeding seasons. The vantage point at Orielton Lagoon is on land at its northern end, where Frogmore Creek empties into the lagoon. All other localities are islands, islets or rocks projecting through the water’s surface. I. = Island; E = east, NE = north-east, NW = north- west, SE = south-east.

Locality Coordinates Region No. of seasons Average no. of nests

Kelp Gull Pacific Gull

Arch Rock 43°17′S, 147°11′E SE 5 62 2 Barren I. 42°49′S, 147°32′E SE 10 21 1 Betsey I. 43°03′S, 147°29′E SE 3 40 1 Charity I. 43°20′S, 147°02′E SE 6 19 6 Curlew I. 43°26′S, 147°10′E SE 17 11 26 Fulham I. 42°55′S, 147°47′E SE 4 39 12 Garden I. 43°16′S, 147°08′E SE 2 6 0 Governor I. 41°52′S, 148°19′E E 6 6 2 Green I. 43°12′S, 147°17′E SE 17 483 7 Hog I. 42°57′S, 147°39′E SE 11 38 3 Howie I. 40°44′S, 144°58′E NW 2 0 132 Huon I. 43°17′S, 147°08′E SE 3 126 1 Iron Pot 43°04′S, 147°25′E SE 7 2 2 Isle of Caves 42°54′S, 147°39′E SE 5 43 0 King George I. 42°57′S, 147°49′E SE 3 23 4 Lachlan I. 42°39′S, 147°58′E E 15 174 18 Orielton Lagoon 42°47′S, 147°32′E SE 9 106 0 Paddys I. 41°24′S, 148°18′E NE 5 4 103 Slopen I. 42°57′S, 147°39′E SE 3 2 2 Smooth I. 42°56′S, 147°47′E SE 3 13 1 Spectacle I. 42°52′S, 147°36′E SE 6 2 6 Susie Islet 42°48′S, 147°32′E SE 7 4 0 Visscher I. 42°51′S, 147°59′E E 6 162 7

at this island. At , there was a highly significant 183 nests for the 5 breeding seasons spanning increase in number of Kelp Gull nests over the 23-year 2003–2008. No Pacific Gull nests were seen at Orielton period of the survey (P <0.001: Figure 6). The number Lagoon in any of the years of the study. of Pacific Gull nests here also significantly increased (P <0.01: Figure 6), but at a much lower rate, so that the Discussion average number of Kelp Gull nests (38) exceeded that of the Pacific Gull (3) (Table 1). Species competition and dominance A second group of 18 survey sites had insufficient annual visits to allow meaningful analyses of trends (Figure 7). Despite evidence for frequent co-occurrence of Kelp However, the mean maximum number of nests for each and Pacific Gulls at breeding sites in Tasmania, all large species given in Table 1, averaged over all the breeding colonies (>100 nests) were numerically dominated by a seasons in which visits to a site were made, provides single species. The stronghold of the breeding populations information on the numbers of the two species of large gull of the Kelp Gull is in the Estuary of the Derwent River and relative to each other. For example, at Arch Rock, visits the various bays, channels and lagoons of the south-east. were made in 5 breeding seasons and yielded averages of Even so, despite the dominance of the Kelp Gull on most 62 Kelp Gull nests versus 2 Pacific Gull nests. No upward of the islands in the south-east whenever the two species or downward trend for either species was discernible co-exist, there are two islands where the Pacific Gull (Figure 7). Similar deductions can be made for almost breeds in larger numbers than the Kelp Gull: Spectacle all of the other 17 sites, with the exception of Orielton and Curlew Islands. The size of the breeding population Lagoon, where a polynomial regression on number of Kelp of the Pacific Gull in the south-east is never large, with the Gull nests in 1991–2008 was highly significant (P <0.001). average number of nests not exceeding 26. This contrasts At that location, an average of 9 Kelp Gull nests was with the Kelp Gull, where six of the localities in the south- observed during the 4 breeding seasons in which visits east averaged at least 40 nests. The pattern of dominance were made before 2000, compared with an average of changes as one moves north up the eastern coast of Are Kelp Gulls replacing Pacific Gulls in Tasmania? 51

Green Island Number of nests Number of nests

Breeding year Breeding year

Figure 2. Number of Kelp Gull (filled circles) and Pacific Figure 3. Number of Kelp Gull (filled circles) and Pacific Gull (filled squares) nests observed on Green Island, Gull (filled squares) nests observed on Barren Island, D’Entrecasteaux Channel, in Tasmania’s south-east, during Pitt Water, in Tasmania’s south-east, during 10 breeding 17 breeding seasons between 1985 and 2008. seasons between 1988 and 2009.

Curlew Island Lachlan Island Number of nests Number of nests

Breeding year Breeding year

Figure 4. Number of Kelp Gull (filled circles) and Pacific Figure 5. Number of Kelp Gull (filled circles) and Pacific Gull (filled squares) nests observed on Curlew Island, Gull (filled squares) nests observed on Lachlan Island, D’Entrecasteaux Channel, in Tasmania’s south-east, during off Tasmania’s eastern coast, during 15 breeding seasons 16 breeding seasons between 1985 and 2007. between 1985 and 2007.

Tasmania. Kelp Gull nests predominate at Visscher and by Kelp Gulls. The data in Figures 2–6 show that the Lachlan Islands (in the south), but at Governor Island, number of Kelp Gull nests at the five localities considered their numbers are much lower, and at Paddys Island, Kelp was increasing with time, although the increase was not Gull nests are greatly outnumbered by Pacific Gull nests. always significant. Despite this, Pacific Gull nests, usually North of there, and along the whole of the northern coast of in much lower numbers, appear to be stable at those sites Tasmania, Kelp Gull nests have never been observed. With (with a small but significant decrease observed at Green regard to total population, we detected substantially more Island, a small but significant increase at Hog Island, and Kelp Gull than Pacific Gull nests. This was very apparent at localities such as Green Island, where an average of no significant change at the other three islands). This 483 Kelp Gull nests was counted during an observation suggests that the two species are not locked in a life- period of 17 breeding seasons in the period 1985–2008 or-death battle for dominance or competition for food or compared with an average of 7 Pacific Gull nests during nest-sites at these colonies. They co-occur at the present the same period. However, the question of interest is not time and may continue to do so unless there are changes whether one species is more abundant than the other, (e.g. climatic) that alter the balance between the species. but whether their relative numbers are changing, and Green Island supported the largest colony of Kelp Gulls specifically whether Pacific Gulls are being outcompeted in this study (and Pacific Gulls decreased there) but the 52 Australian Field Ornithology W.C. Wakefieldet al.

Hog Island might not necessarily result in a proportional increase in the predation rate. Similarly, Quintana & Yorio (1998) observed at the same location that Kelp Gull predation of the eggs and chicks of the Imperial Cormorant Phalacrocorax atriceps, occurring mainly at peripheral nests of the latter’s breeding colony, did not significantly impact the breeding success of the cormorants. Bertellotti & Yorio (1999) analysed the diet of Kelp Gulls at three colonies in coastal Patagonia from regurgitated pellets, and identified 41 types of prey. Kelp Gulls there fed throughout the season mostly on

Number of nests intertidal invertebrates, although fish were also important, mainly during the chick stage. The diet also included garbage, insects, and the offspring of other seabirds. Of all types of prey, 70.7% were common to the three locations, although the pattern of consumption of the main food categories differed. The average consumption of garbage differed significantly among locations, with more garbage Breeding year in the diet the closer the colony was to the nearest landfill. Figure 6. Number of Kelp Gull (filled circles) and Pacific Further west, in the Lake District of Argentina that borders Gull (filled squares) nests observed on Hog Island, on Chile, Frixione et al. (2012) studied the diet of the Kelp Frederick Henry Bay, during 11 breeding seasons between 1986 and 2008. Gull in the De La Guardia Islands in Lake Nahuel Huapi, and found that the breeding colony was being sustained by waste from the refuse tip of the nearby resort town of Villa la Angostura. Supplementing the diet of insects and third largest colony of Kelp Gulls in the south-east was at fish, the anthropogenic source of food was important in Orielton Lagoon, in a mainland habitat where no Pacific sustaining the breeding colony of the Kelp Gull. Still further Gulls were found breeding, showing that part of the north, off the Chilean coast, on Damas, Pajaros and historical increase in Kelp Gulls has involved occupation of Chañaral Islands, colonies of Kelp Gulls exhibited a very new habitats not used by Pacific Gulls. wide range of feeding habits, which differed from island to island. For example, at Damas Island, crustaceans Although it is tempting to attribute any apparent and insects were numerous in the diet, but no waste was displacement of the Pacific Gull by the Kelp Gull at places found (Ludynia et al. 2005), whereas on Pajaros Island where it might be occurring to more aggressive behaviour (close to the large towns of Coquimbo and La Serena) of the latter species, there is an alternative explanation. anthropogenic sources of food rivalled fish as the most The reduction in the range of the Pacific Gull in eastern important food source (Ludynia et al. 2005; Villablanca et Australia was noted by Serventy et al. (1971, p. 200), who al. 2007). In stark contrast, on Chañaral Island, olive seeds surmised that this shrinkage might have “left an ecological (presumably obtained from a plantation 10 km away) were niche which was in the process of being filled” by the Kelp found in 86% of all Kelp Gull pellets (Ludynia et al. 2005). Gull. Therefore, there is no imperative to believe that the Kelp Gull is forcing a reduction in Pacific Gull numbers. In South Africa, the population of the Kelp Gull The IUCN Red List of threatened species lists the status L. d. vetula numbered ~10 000 pairs from 1976–1977 to of the Pacific Gull as ‘Least Concern’, with the population 1980–1981, increased to 21 000 pairs from 2000–2001 trend as ‘stable’ (http://www.iucnredlist.org/search). This is to 2004–2005, and then decreased to 17 500 pairs from despite the fact that the population trend of the Kelp Gull is 2009–2010 to 2013–2014 (Whittington et al. 2016). These seen as ‘increasing’ (e.g. see Dann 2007). authors attributed these changes to fluctuations in the number of birds breeding on islands off the western coast of South Africa, after increases followed cessation of Kelp Gull trends worldwide and predation by controls on Kelp Gulls there in the 1970s. The increases this species on other coastal species were associated with supplementary food provided by fisheries and landfill sites, giving this opportunistic and Because Kelp Gulls occur outside Australia, information generalist species an additional source of food, whereas on any changes in their numbers, and how they interact the decreases were influenced by substantial predation of with other closely related species of gulls or terns in other chicks by Great White Pelicans Pelecanus onocrotalus. continents, may shed light on how their numbers could On islands where the number of Kelp Gulls has increased, change in Australia. For example, on the eastern coast of predation by this species on eggs and chicks of threatened Patagonia (Argentina), predation by Kelp Gulls at Punta seabirds is thought to have contributed to decreases in León impinged upon the populations of the Royal Tern those species, and controls on Kelp Gulls have been re- maximus (Sterna maxima) and Cayenne Tern introduced (Whittington et al. 2016). As a result of human T. eurygnathus (S. eurygnatha) (Yorio & Quintana 1997). activity, several new foraging habitats have become During a 3-year study, these authors found that Kelp Gulls available to the Kelp Gull, including croplands, fishing were the main predator of tern eggs, accounting for 99% of harbours and refuse dumps, and supplementary food 454 observed predations. Nevertheless, overall predation sources at these new foraging habitats were deemed likely on tern eggs was restricted to only a few individual Kelp to be the cause of the population increase in the late 20th Gulls, whose nests were situated close to the periphery century (Steele 1992). This was attributed to the fact that of the tern colony, and Yorio & Quintana (1997) concluded Kelp Gull chicks are fed predominantly on ‘natural’ prey, that the expansion of Kelp Gull numbers at Punta León which indicates that the population increase may not be Are Kelp Gulls replacing Pacific Gulls in Tasmania? 53

80 ArchArch RockRock BetseyBetsey Island Island CharityCharity Island Island FulhamFulham Island Island 100 40 100

60 75 30 75

40 50 20 50

20 25 10 25 Number of nests

0 0 0 0 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010

Breeding year

Garden Island Governor Island Howie Island Huon Island 8 20 200 250 Garden Island Governor Island Howie Island 160 200 Huon Island 6 15

120 150

4 10 80 100

2 5 40 50 Number of nests

0 0 0 0 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010

Breeding year

4 Iron Pot Isle of Caves King George Island Orielton Lagoon 120 50 300 Iron Pot Isle of Caves King George Island Orielton Lagoon 250 3 40 80 200 30 2 150 20 40 100 1 10 50 Number of nests

0 0 0 0 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010 1990 1995 2000 2005 2010

Breeding year

Paddys Island Slopen Island Smooth Island Spectacle Island Paddys Isand Slopen Island 25 Smooth Island 16 Spectacle Island 160 5

4 20 120 12

3 15 80 8 2 10

40 4

Number of nests 1 5

0 0 0 0 1990 1995 2000 2005 1995 2000 2005 2010 1995 2000 2005 2010 1985 1990 1995 2000 2005 2010

Breeding year

Susie Islet Visscher Island 500 8 Susie Islet Visscher Island 400 6

300

4 200

2 100 Number of nests

0 0 1980 1985 1990 1995 1985 1990 1995 2000

Breeding year

Figure 7. Number of Kelp Gull (filled circles) and Pacific Gull (filled squares) nests observed on 17 islands (including islets and rocks projecting through the water’s surface) and one land-based vantage point (Orielton Lagoon) in Tasmania that were visited in <10 breeding seasons. Symbols show the maximum number of nests observed in the specified year’s breeding season. In all graphs, the abscissa represents the breeding year and the ordinate represents the number of nests. 54 Australian Field Ornithology W.C. Wakefieldet al.

because of enhanced reproductive success, but from two decades has provided another food source for both improved post-fledging survival of juveniles, which are species. These developments provide an opportunity to known to aggregate at sites where supplementary food is examine how these two species of gull may respond to provided. these new opportunities. In New Zealand, where Larus dominicanus has been variously known as the Southern Black-backed Gull and Acknowledgements the Dominican Gull as well as the Kelp Gull, Fordham No funding was obtained for this project from any funding (1967) recorded 31 breeding colonies (21 on the mainland body, all expenses being paid from WCW’s own pocket. and 10 on adjacent islands) in the 1963–1964 breeding Ethics Committee approval was obtained from the Department season in an area around Wellington. From historical of Primary Industry, Parks, Water and Environment, Tasmania records, he concluded that the population of this species (Approval No. 26/2008-09). Bird banding was carried out under had grown rapidly in the preceding quarter century, with the authority issued by the Australian Government Department of two meat-works on the edge of the harbour, an abattoir, and the Environment, Water, Heritage and the Arts, Banding Authority at least nine council refuse tips helping to account for the No. 1121. As WCW’s major focus of attention was the banding of estimated 86% by volume of the diet of these scavenging chicks, he possessed various permits from the Parks and Wildlife birds attributable to offal and waste (Fordham 1970). Service to visit offshore islands and carry out the necessary activities (e.g. Permit FA09117). We thank Bruce Robertson for On the Antarctic Peninsula, Silva et al. (2001) showed his comments on an early draft of this paper. Rohan Clarke and that Antarctic Krill Euphausia superba made up 20% by Peter Dann made useful suggestions to improve the manuscript. mass of the diet of adults and 66% of the chicks’ diet in Christine Evans, a Senior Librarian at the University of Tasmania, the Kelp Gull. Fish constituted a low proportion of total assisted with some of the references. prey, both in pellets and chick regurgitations, but limpets (Mollusca) constituted 70% by mass of the diet of adult birds. The authors attributed the high reproductive success References of the Kelp Gull to the quality food resources available in Bertellotti, M. & Yorio, P. (1999). Spatial and temporal patterns in the far south of this species’ breeding range. Unlike South the diet of the Kelp Gull in northern Chubut, Patagonia. Condor America, South Africa, New Zealand and Australia, no 101, 790–798. refuse tips are present in this pristine environment. Branco, J.O., Costa, E.S., de Araujo, J., Durigon, E. & Alves, M.A.S. (2009). Kelp gulls, Larus dominicanus (Aves: Phylogenetic relationship between Pacific ), breeding in Keller Peninsula, King George Island, Antarctic Peninsula. Zoologia 26, 562–566. and Kelp Gulls Burger, J. & Gochfeld, M. (1996). Family Laridae (gulls). In: del Hoyo, J., Elliott, A. & Sargatal, J. (Eds). Handbook of the Birds Pons et al. (2005), in a molecular phylogenetic study of of the World, Volume 3: Hoatzin to Auks, pp. 572–623. Lynx 53 gull species (Laridae), found that the Larus Edicions, Barcelona, Spain. was not monophyletic. Within Larus, L. dominicanus and Close, D.H. (1981). The Kelp Gull in South Australia. South L. pacificus fell into different subclades, the Kelp Gull being Australian Ornithologist 28, 155–156. a solitary Southern Hemisphere species in the ‘White- Coulson, G.M. & Coulson, R.I. (1983). The significance of rubbish headed species’ clade along with 18 Holarctic species, and tips as an additional food source for the Kelp Gull and Pacific the Pacific Gull winding up in a small ‘Band-tailed species’ Gull in Tasmania. MEnvSci thesis. University of Tasmania, clade with a few species from Asia and South America. Hobart. Therefore, despite the similarities of appearance and Coulson, R. & Coulson, G. (1993). Diets of the Pacific Gull Larus feeding habits of these two species, the phylogenies do pacificus and the Kelp Gull Larus dominicanus in Tasmania. not suggest a very close relationship, which could give one Emu 93, 50–53. little cause to believe that they should necessarily occupy Coulson, R. & Coulson, G. (1998). Population change among similar ecological niches. Pacific, Kelp and Silver Gulls using natural and artificial feeding sites in south-eastern Tasmania. Wildlife Research 25, 183–198. Future studies Dann, P. (2007). The population status of the Kelp Gull Larus dominicanus in Victoria. Corella 31, 73–75. D’Ombrain, A.F. (1973). Dominican Gull – an early sighting. In Tasmania, although both species of large gull studied Australian Bird Bander 11, 10. here have a wide range of food sources, Kelp Gulls are Ford, J. (1965). The avifauna of the islands between Dongara and more likely to be seen at refuse-disposal sites than are Lancelin, Western Australia. Emu 64, 181–203. Pacific Gulls, the latter preferring natural shoreline sites Fordham, R.A. (1967). History and status of the Dominican Gull in (Coulson & Coulson 1983). It is therefore of interest to Wellington. Notornis 14, 144–153. see how changes in waste management might affect gull Fordham, R.A. (1970). Mortality and population change of populations, particularly of the Kelp Gull. Conversion of Dominican Gulls in Wellington, New Zealand. Journal of Animal metropolitan tips to waste-transfer stations since 1980 in Ecology 39, 13–27. the Hobart and Glenorchy areas has already decreased Frixione, M.G., Casaux, R., Villaneuva, C. & Alarcón, P.A.E. food availability for scavenging gulls. Future further (2012). A recently established Kelp Gull colony in a freshwater decreases are expected, as the Hobart City Council plans environment supported by an inland refuse dump in Patagonia. to cease operating the landfill site in McRobies Gully by Emu 112, 174–178. 2030. Concomitantly, the rapid expansion of fish farming Higgins, P.J. & Davies, S.J.J.F. (Eds) (1996). Handbook of of Atlantic Salmon Salmo salar in the D’Entrecasteaux Australian, New Zealand & Antarctic Birds, Volume 3: Snipe to Channel and around the in the past Pigeons. Oxford University Press, Melbourne. Are Kelp Gulls replacing Pacific Gulls in Tasmania? 55

Ludynia, K., Garthe, S. & Luna-Jorquera, G. (2005). Seasonal Wall, L.E. (1956). The Southern Black-backed Gull in Tasmania. and regional variation in the diet of the Kelp Gull in Northern Emu 56, 433. Chile. Waterbirds 28, 359–365. Warneke, R. & Dann, P. (2013). Birds of Seal Rocks in northern McGill, A.R. (1943). Probable occurrence of the Southern Black- Bass Strait: Changes over forty years (1965–2005). Victorian backed Gull (Larus dominicanus) in Australia. Emu 43, 65–66. Naturalist 130, 4–21. Menkhorst, P., Rogers, D., Clarke, R., Davies, J., Marsak, P. Watson, G.E. (1975). Birds of the Antarctic and Sub-Antarctic. & Franklin, K. (2017). The Australian Bird Guide. CSIRO American Geophysical Union, Washington. Publishing, Melbourne. Whittington, P.A., Crawford, R.J.M., Martin, A.P., Randall, Pons, J.-M., Hassanin, A. & Crochet, P.-A. (2005). Phylogenetic R.M., Brown, M., Ryan, P.G., Dyer, B.M., Harrison, K.H.B., relationships within the Laridae (: Aves) Huisamen, J., Makhado, A.B., Upfold, L., Waller, L.J. & inferred from mitochondrial markers. Molecular Phylogenetics Witteveen, M. (2016). Recent trends of the Kelp Gull (Larus and Evolution 37, 686–699. dominicanus) in South Africa. Waterbirds 39 (Special Quintana, R.D. & Travaini, A. (2000). Characteristics of nest sites Publication 1), 99–113. of Skuas and Kelp Gull in the Antarctic Peninsula. Journal of Wolfe, T.O. (1969). Nesting of the Dominican Gull — first Field Ornithology 71, 236–249. Tasmanian record. Tasmanian Naturalist 17, 4. Quintana, F. & Yorio, P. (1998). Kelp Gull Larus dominicanus Yorio, P. & Quintana, F. (1997). Predation by Kelp Gulls Larus predation on an Imperial Cormorant Phalacrocorax atriceps dominicanus at a mixed-species colony of Royal and Cayenne colony in Patagonia. Marine Ornithology 26, 84–85. Terns Sterna maxima and S. eurygnatha in Patagonia. Ibis 139, Serventy, D.L., Serventy, V. & Warham, J. (1971). The Handbook 536–541. of Australian Sea-birds. A.H. & A.W. Reed, . Yorio, P., Bertellotti, M., Gandini, P. & Frere, E. (1998). Kelp Sibley, C.G. & Monroe, B.L. (1990). Distribution and Gulls Larus dominicanus breeding on the Argentine coast: of Birds of the World. Yale University Press, New Haven, Population status and relationship with coastal management Connecticut, USA. and conservation. Marine Ornithology 26, 11–18. Silva, M.P., Favero, M., Copello, S. & Bastida, R. (2001). Does access to high-quality pelagic prey increase the breeding success of Kelp Gulls Larus dominicanus in the Antarctic Peninsula? Marine Ornithology 28, 85–88. Received 7 August 2018, accepted 7 November 2018, Steele, W.K. (1992). Diet of Hartlaub’s Gull Larus hartlaubii and published online 26 April 2019 the Kelp Gull Larus dominicanus in the southwestern Cape Province, South Africa. Ostrich 63, 68–82. Thomas, D.G. (1967). The Dominican Gull in Tasmania. Emu 66, 296. Villablanca, R., Luna-Jorquera, G., Marín, V.H., Garthe, S. & Simeone, A. (2007). How does a generalist seabird species use its marine habitat? The case of the kelp gull in a coastal upwelling area of the Humboldt Current. ICES Journal of Marine Science 64, 1348–1355.