Case Study: Responses of Penguin Populations to Climate Change Along the West Antarctic Peninsula
Apex predators including seabirds, such as Adélie penguins and Crabeater seals, require sea ice as a platform for foraging, breeding, and other activities to successfully complete their life cycles. The pack ice seals, crabeater (Lobodon carcinophagus), Weddell (Leptonychotes weddellii), leopard (Hydrurga leptonyx), and Ross (Ommatophoca rossii) all breed within the ice pack. Adélie penguins (Pygoscelis adéliae) are also ice-obligate, requiring winter sea ice (Ribic et al., 2008) to afford optimal access the foraging areas, but they breed on land in the Austral summer. Each of these species presents interesting contrasts that illuminate the understanding of how polar species are responding to regional climate change.
The local Adélie penguin rookeries near Palmer Station on southwest Anvers Island have declined in size by almost 80 percent since modern observations started in 1975. At the same time, two congeneric, but subantarctic, ice-tolerant or ice-avoiding species, the Gentoo (Pygoscelis papua) and Chinstrap penguins (Pygoscelis antarctica) have immigrated into the region, in many cases establishing nesting sites in areas formerly occupied by Adélie pairs. Gentoos and Chinstraps now make up about half the total penguin population in the region. Anomalously low sea ice extent in 1989-90 following the 1988-89 La Nina event may have signaled a tipping point from which the system has not been able to recover. The case of Adélie penguins is valuable because these ocean-foraging, land-breeding birds appear to be responding to both marine and terrestrial forcings. Their decline has roughly paralleled the regional decline in sea ice extent and duration, and also declines in favored prey species including the Antarctic krill (Euphausia superba) and the Antarctic silverfish (Pleurogramma antarctica).