Contrasting population changes in sympatric penguin species in association with climate warming

Abstract

Climate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less iceadapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long-term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous interannual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice-free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic-mediated changes cascading from global climate forcing.

Post-breeding dispersal of Adélie penguins (Pygoscelis adeliae) nesting at Signy Island, South Orkney Islands

“…Predicted future declines in krill numbers in the Scotia Sea, associated with more frequent warm periods and the shorter duration of winter sea ice Ross 2001, 2003;Atkinson et al 2004Atkinson et al , 2008Murphy et al 2007) may reduce birds' abilities to rebuild body reserves in time for the succeeding breeding season. Continued future declines in breeding success and over-winter survival are likely consequences (Fraser and Hofmann 2003;Smith et al 2003;Lynnes et al 2004;Forcada et al 2006;Forcada and Trathan 2009). Further research will be necessary to determine whether or not Adélie penguins consistently utilize the same migratory routes and wintering grounds in different years.…”

“…The clear dependence of Adélie penguins on sea ice for both moulting and foraging means that any further reductions in either sea ice distribution or concentration, resulting from climate change, would potentially impose increased pressure upon these populations (Forcada et al 2006;Hinke et al 2007;Forcada and Trathan 2009). Predicted future declines in krill numbers in the Scotia Sea, associated with more frequent warm periods and the shorter duration of winter sea ice Ross 2001, 2003;Atkinson et al 2004Atkinson et al , 2008Murphy et al 2007) may reduce birds' abilities to rebuild body reserves in time for the succeeding breeding season.…”

“…Long-term population studies of Adélie penguins (Pygoscelis adeliae) breeding at Signy Island in the South Orkney Islands have shown an irregular annual decline in numbers over the period 1987-2010, in parallel with regional warming and reduction in the seasonal sea ice (Forcada et al 2006(Forcada et al , 2008Turner et al 2009). Thus, as penguin population size and reproductive performance are known to be related to sea ice, weather and oceanographic conditions (Trathan et al 1996;Forcada and Trathan 2009), understanding how they utilize their environment and available resources is critical.…”

“…In winter, Adélie penguins are thought to feed on small fish and Antarctic krill Euphausia superba, the latter also being one of the key summer diet species in the West Antarctic Peninsula and Scotia Sea (Ainley et al 1994(Ainley et al , 1998. The population dynamics of Antarctic krill are also influenced by environmental conditions, including annual change in sea ice extent and duration Ross 2001, 2003;Atkinson et al 2004Atkinson et al , 2008Murphy et al 2007), so information on their biomass and distribution is of major importance in understanding penguin population trajectories in the West Antarctic Peninsula and Scotia Sea sectors (Lishman 1985;Fraser and Hofmann 2003;Lynnes et al 2004;Forcada et al 2006;Hinke et al 2007). Consequently, knowledge of the winter foraging distribution and behaviour of Adélie penguins is important if the relationships between sea ice, prey abundance and population mechanisms, together with climate-mediated change, are to be properly understood.…”

“…Further, variations in the timing of sea ice coverage have been linked to physical forcing driven by the El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM) (Yuan and Martinson 2000;Yuan 2004;Turner 2004;Stammerjohn et al 2008b). Indeed, this environmental perturbation is now thought to be generating ecological responses in numerous species, including Antarctic penguin populations Smith et al 2003;Forcada et al 2006;Forcada and Trathan 2009). …”