Notornis Vol 52 Part 4.Indd

206 Notornis, 2005, Vol. 52: 206-214 0029-4470 © The Ornithological Society of New Zealand, Inc. 2005 Population changes and biology of the Antipodean wandering albatross (Diomedea antipodensis) KATH WALKER 549 Rocks Road, Nelson, New Zealand. [email protected] GRAEME ELLIOTT 549 Rocks Road, Nelson, New Zealand. Abstract The Antipodean wandering albatross (Diomedea antipodensis) is endemic to Antipodes Island in the New Zealand subantarctic. A programme of regular census and population study was initiated on Antipodes Island in 1994 to determine the status of the species. This paper reports on field work carried out every summer from 1994 to 2005. Aspects of breeding biology are described and compared with those of other species of wandering albatross, particularly the closely related Gibson’s wandering albatross (D. gibsoni) on Adams Island. Average annual survival over 10 years was 0.957. Productivity was measured over 11 years and averaged 0.74 chicks per nesting pair. Survivorship was similar to that in the increasing Diomedea exulans population on Crozet Island, and productivity higher than recorded in all other wandering albatross populations. Between 1994 and 1997, the average annual number of pairs nesting on Antipodes Island was 5136. There is evidence of population decline during the 1970s but numbers are now increasing. Walker, K.; Elliott, G. 2005. Population changes and biology of the Antipodean wandering albatross (Diomedea antipodensis). Notornis 52(4): 206-214. Keywords Population; productivity; survival; Antipodean wandering albatross; Diomedea antipodensis; Antipodes Islands INTRODUCTION yrs) and produce a chick at two-three year intervals The wandering albatrosses, with their huge wing and, therefore, are less able to sustain increased spans and graceful soaring flight, have long been bycatch-induced mortality than many other seabird symbols of the southern oceans, and were described species (Croxall & Rothery 1991; Gales 1998). by Linnaeus, as Diomedea exulans, as early as 1758, In 1994 we began a long-term study of However, until recently, almost nothing was Antipodean wandering albatross on Antipodes known of the New Zealand populations, although Island to determine population size and trends, and they comprise over half of the world’s wandering the key demographic parameters necessary for an albatrosses (Gales 1998). understanding of conservation status. In this paper The much-studied wandering albatross we provide estimates of breeding success and adult (D. exulans) of the south Indian and south Atlantic survival in 1994-2004 and describe population size oceans was known to have suffered population and trends over the last 30 years. declines at all of its colonies between the 1960s and Most Antipodean wandering albatrosses nest 1990s, attributed to long-line fishing in the southern on Antipodes Island, but about six pairs nest on oceans (Weimerskirch & Jouventin 1987; Croxall et Campbell Island, about 1000 km to the south west al. 1990; de la Mare & Kerry 1994; Weimerskirch et al. (Gales 1998), and in 2005 a pair bred on Pitt Island 1997). There were fears the two wandering albatross in the Chatham Island group about 700 km to the taxa endemic to New Zealand, Gibson’s wandering north (C. Miskelly, pers comm.). Prior to 1994, most albatross (D. gibsoni) and Antipodean wandering information on the species came from a study of albatross (D. antipodensis), may have suffered distribution and nesting density on Antipodes Island similarly, as both have been a regular bycatch in in the summer of 1969 (Warham & Bell 1979) and long-line fisheries (Murray et al. 1993). Wandering from examination of dead birds caught as fisheries albatrosses are long-lived (>40 yrs), breed late (≥10 bycatch off the east coast of New Zealand (Murray et al. 1993). The Antipodes Islands, 850 km south-east of New Received 8 August 2005; accepted 25 September 2005 Zealand in the south-west Pacific Ocean, comprise Editor M. Williams one large and six smaller islands (Fig. 1). Antipodes Population changes of Antipodean albatross 207 Island (49° 41’ S, 178° 47’ E) is approximately 7 x 5 during or soon after incubation usually return to km (2025 ha), and comprises cliff-edged or steep breed in the following season, but most successful coastal slopes of 100 - 200 m height and a gentler breeders and those that fail after incubation, usually upland rising to two peaks of 366 m and 358 m wait at least a year before attempting to breed again. near its centre. The island is mostly covered with A few birds do not return to the breeding island Poa litorosa tussock, with only two species of low- for three or four years. Estimates of adult survival growing woody shrub, Coprosma rugosa antipoda were calculated from banding and recovery data and C. ciliata. The steep coastal slopes are covered in using the multi-strata formulation of Brownie et al. 1-2 m high dense vegetation comprising tall pedestals (1993) and Hestbeck et al. (1991) implemented in the of Poa litorosa intertwined with Poa foliosa, and the program MARK (White & Burnham 1999). Details ferns Blechnum durum and Asplenium obtusatum. They of this method are described in Elliott & Walker are extensively burrowed by seabirds, particularly (2005). We used AIC (Burnham & Anderson 2002) white-headed petrels (Pterodroma lessonii) and grey to determine whether our data supported different petrels (Procellaria cinerea). On the flatter uplands survival estimates for male and female albatrosses. and plains, the vegetation comprises stunted and Breeding success was compared at three different widely–spaced Poa litorosa with low-growing ferns and widely separated sites (study area 29 ha, Pipit and herbs in the disturbed and enriched soils around Peak 19 ha, Block-32 21 ha; Fig. 2) by counting albatross nests. the number of nests containing eggs in early-mid Antipodes Island is one of the world’s least February, just after laying was completed, and by modified islands. It has been inhabited for short counting the number of chicks present in December periods only by sealers, shipwrecked castaways just before they commenced fledging. The number and researchers. Although farm cattle, sheep and of chicks which finally fledged was only measured goats, and some trees and grasses, were deliberately in the study area where the marked nest sites were introduced in the late 1800s (Warham & Johns, 1975), re-visited at the end of the season and again the they quickly died out and the only lasting additions to following summer to look for dead banded chicks the biota are a few weedy herbs (Godley 1989), house who failed to fledge. Differences in breeding success mice (Mus musculus), and some birds self-introduced between years and between sites were examined by from New Zealand (Warham & Bell 1979). logistic regression. Antipodean wandering albatrosses do not breed From 1998, all newly constructed nests present amongst the tall vegetation on the steep coastal in the study area at the beginning of the breeding slopes, or amongst the tall Polystichum vestitum fern season were marked, mapped, and checked every on poorly drained parts of the upland. However, the one or two days to determine the timetable of egg remaining 1062 ha of the island is all occupied by laying, the length of incubation shifts, and the nest nesting albatrosses, effectively comprising one large failure rate during incubation. colony. This contrasts with most other wandering Nest site fidelity was assessed in 1996 by albatross populations where colonies occur in discrete searching for the last nest used by birds breeding habitat patches or on separate islands. in the study area and measuring, with compass and tape measure, the distance and direction moved METHODS between nest sites. From 1994 to 2005 we visited Antipodes Island To determine the current size of the Antipodean every summer between December and March. wandering albatross population, the island was In a 29 ha study area near the north end of the island divided into 36 blocks separated by topographical (block 1 in Fig. 1), we banded all nesting albatrosses features (Fig. 1). Thirty-one of the 36 blocks and mapped and marked their nests. In 1994-1997 contained nesting albatrosses. In 1994 (Clark et al. birds were banded only with a numbered stainless 1995), 1995 (Amey et al. 1995) and 1996 (this paper) steel band, but during 1998-2005 all metal-banded nests with eggs in all the albatross-occupied blocks birds were also fitted with a coloured plastic band were counted during February. In 1997, only 17 engraved with large numbers which could be read of the 31 blocks were counted. Within each block from a distance. The coloured bands increased the two - four observers spread out so that they were chances of band recoveries and reduced the need for 20 - 25 m apart, and walked in parallel lines through catching birds. the block, zigzagging where necessary to cover all Adult wandering albatrosses show strong the ground. Observers on the outside marked the fidelity to their colony and nest site (Inchausti edges of the counted strip with fluorescent tape or & Weimerskirch 2002) and their survival can be spray paint so that the same ground was not counted calculated from annual checks for banded birds in the twice. In 1994 and 1995 each nest was marked with study colony. However, the birds’ deferred breeding a spot of paint to show it had been counted. strategy (Tickell 1968) complicates measurement of To determine population trends, nests in three of adult survival. Birds that fail in their nesting attempt the blocks were counted annually from 1997 (study 208 Walker & Elliott Figure 1 Antipodean wandering albatross census blocks on Antipodes Island. area, MCBA and Block 32; Fig.2). These three blocks to repeat several of the methods used to assess the were chosen because they had large populations albatross population prior to our study.

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