Population Size and Decadal Trends of Three Penguin Species Nesting at Signy Island, South Orkney Islands

Abstract

We report long-term changes in population size of three species of sympatrically breeding pygoscelid penguins: Adélie (Pygoscelis adeliae), chinstrap (Pygoscelis antarctica) and gentoo (Pygoscelis papua ellsworthii) over a 38 year period at Signy Island, South Orkney Islands, based on annual counts from selected colonies and decadal all-island systematic counts of occupied nests. Comparing total numbers of breeding pairs over the whole island from 1978/79 to 2015/16 revealed varying fortunes: gentoo penguin pairs increased by 255%, (3.5% per annum), chinstrap penguins declined by 68% (-3.6% per annum) and Adélie penguins declined by 42% (-1.5% per annum). The chinstrap population has declined steadily over the last four decades. In contrast, Adélie and gentoo penguins have experienced phases of population increase and decline. Annual surveys of selected chinstrap and Adélie colonies produced similar trends from those revealed by island-wide surveys, allowing total island population trends to be inferred relatively well. However, while the annual colony counts of chinstrap and Adélie penguins showed a trend consistent in direction with the results from all-island surveys, the magnitude of estimated population change was markedly different between colony wide and all island counts. Annual population patterns suggest that pair numbers in the study areas partly reflect immigration and emigration of nesting birds between different parts of the island. Breeding success for all three species remained broadly stable over time in the annually monitored colonies. Breeding success rates in gentoo and chinstrap penguins were strongly correlated, despite the differing trends in population size. This study shows the importance of effective, standardised monitoring to accurately determine long-term population trajectories. Our results indicate significant declines in the Adélie and chinstrap penguin populations at Signy Island over the last five decades, and a gradual increase in gentoo breeding pairs.

Bacterial community composition in Adélie (Pygoscelis adeliae) and Chinstrap (Pygoscelis antarctica) Penguin stomach contents from Signy Island, South Orkney Islands

“…Signy Island, part of the South Orkney Island archipelago, hosts sympatrically breeding populations of Adélie (Pygoscelis adeliae) and Chinstrap (P. antarctica) Penguins with total island populations of 18,333 and 19,530 pairs, respectively (Dunn et al 2016).…”

Niche partitioning of sympatric penguins by leapfrog foraging appears to be resilient to climate change

“…The behaviour‐based model reveals that niche partitioning by leapfrog foraging is reduced as the degree of allochrony between the two species is reduced, but the analysis of long‐term phenology data shows that allochrony is preserved as air temperatures warm and penguin laying dates advance. We conclude that competitor matching due to differing rates of phenological response to environmental change is unlikely to arise among the two species and will not be a significant contributing factor to the population declines observed for these two species across the WAP and Scotia Sea (Dunn et al., ; Lynch, Naveen, et al., ; Trivelpiece et al., ). These declines are more likely to be driven by changes in recruitment rates of Antarctic krill, recovery of the populations of other competitors such as baleen whales or direct weather effects upon penguin breeding success (Lynch, Naveen, et al., ; Trivelpiece et al., ).…”

Predicting Which Species Succeed in Climate-Forced Polar Seas

“…Recent studies from a number of sites located across the WAP and Scotia Sea region have provided strong evidence of shifts in the distribution of both Adélie (Pygoscelis adeliae) and chinstrap (Pygoscelis antarctica) penguin populations (Croxall et al, 2002;Dunn et al, 2016). However, the role played by sea ice dynamics in influencing the population trends of uppertrophic predators (both pagophilic and pagophobic) is complex.…”