Unexpected effects of climate change on the predation of Antarctic petrels

Abstract

Antarctic petrels Thalassoica antarctica on Ardery Island, Antarctica (66°S, 110°E), experienced major reductions in breeding success and breeder survival over four seasons between 1984/85 and 1996/97. In 1996 the reason was revealed. A large snowdrift covered part of the study colony on the cliffs. Southern giant petrels Macronectes giganteus, normally lacking access to this area, exploited the snow for soft ‘crash landings”. After landing they waited for the disturbed birds to resettle on their nests and then used surprise to seize and kill a victim. Predation continued into the egg period, and only stopped after the snowdrift had melted. Giant petrels showed no interest in the eggs but, during the panic caused by their activities, South Polar skuas Catharacta maccormicki took the deserted eggs. Antarctic petrel mortality due to predation within the 1996/97 season amounted to 15.4% of experienced breeders, and breeding success was reduced to virtually zero. Weather data from the nearby Casey station over the 1980–96 period showed that a significant increase in precipitation has occurred, in combination with shifts in speed and direction of winds. We conclude that the decreases in breeding success and survival in earlier seasons were also related to increased snowfall and predation. Although similar predation behaviour by giant petrels has not been reported before, we think that it is long established and explains why nesting of the smaller fulmarine petrels is limited to steeper cliffs or sheltered sites. The complexity of the response seems unlikely to be predicted by our present understanding of how climate change affects ecosystems.

Stable isotopes reveal trophic segregation by sex and age in the southern giant petrel in two different food webs

“…Conroy 1972, Hunter 1984, Cooper et al 2001, the slow growth rates of the chicks, deferred maturity and long life-span (Conroy 1972, Hunter 1984 make it an ideal model to study intraspecific trophic segregation. This species shows a noticeable sexual segregation in diet and foraging areas (Hunter 1983, Hunter & de Brooke 1992, González-Solís et al 2000a, Van Franeker et al 2001, Quintana & Dell'Arciprete 2002, Le Bohec et al 2003, Patterson & Fraser 2003, González-Solís & Croxall 2005, as well as in chick-provisioning rate and meal size of chick feedings (Hunter 1983, Hunter & Brooke 1992. However, research on intraspecific variation in diet in this and other seabird species has been limited by conventional methodologies, such as the analysis of gut contents or direct observation of birds at sea (Hobson et al 1994).…”

Climate change and its impact on Australia's avifauna

“…Observations of breeding colonies of the Antarctic Petrel (Thalassoica antarctica) illustrate how a fairly subtle environmental change can have disastrous consequences for the reproductive success of a prey population by altering the behaviour of a predator (Van Franeker et al 2001). Snowfall from 1980 to 1996 increased at Casey Station in the Antarctic, leading to large, persistent snowdrifts in areas that had previously remained bare.…”

Variations of snow petrel breeding success in relation to sea-ice extent: detecting local response to large-scale processes?

“…Croxall et al (2002) suggest that polynyas are favoured by foraging snow petrels. However, snow petrels may be dependent on other types of sea-ice habitats rather than solely on large areas of open water (despite the potential presence of marginal ice zones within these polynyas) because of their feeding behaviour, which consists of scavenging at the edge, in open water or loose ice leads within the pack ice itself (Ainley et al 1993;Chastel et al 1993;van Franeker 2001). Therefore, the pixel size over which areas of open water were calculated (625 km 2 ) may be too large to detect such finer scale effect of sea-ice/open water characteristics.…”

“…1). Observations were conducted every season by one or two observers appropriately trained using a set of guidelines (van Franeker 1991). Nests were visually inspected regularly throughout the breeding season.…”

“…With a circumpolar distribution, this medium sized petrel (250-500 g) breeds in large numbers on ice-free areas along the coast of the Antarctic continent, on nearby islands and inland (Croxall 1995), but is mostly found in close association with open or broken sea-ice, foraging within the marginal ice zone (Griffith 1983;Ainley et al 1984;Veit and Hunt 1991;van Franeker 2001) where it feeds predominantly on fish, cephalopods and crustaceans such as krill (Ainley et al 1984;Ridoux and Offredo 1989;van Franeker 2001). By exploiting this particular niche, snow petrels are most likely to be exposed to the effects on sea-ice of a potential climatic shift in the Southern ocean ecosystem (Weismerkirch et al 2003) and their demography may reflect these changes, which may in turn be detected through longterm studies.…”