Adelie penguin 1:2 chick nest ratio, 1991 - 2017.

• Main Authors: LTER, Palmer Station Antarctica, Fraser, William
• Format: Dataset
• Language: English
• Published: Environmental Data Initiative 2020
• Subjects: Antarctic; Adelie penguin; Antarc*; Sea ice
• Online Access: https://dx.doi.org/10.6073/pasta/92327f1e6e1c22a0f5d31a5f385f05ae; https://portal.edirepository.org/nis/mapbrowse?packageid=knb-lter-pal.86.6

The fundamental long-term objective of the seabird component of the Palmer LTER (PAL) has been to identify and understand the mechanistic processes that regulate the mean fitness (population growth rate) of regional penguin populations. Two hypotheses have guided this research, with one suggesting that population mean fitness is best explained by changes in regional krill biomass, and the other proposing that long-term changes in sea ice affects mean fitness by tipping the balance in favor of one species over another in accordance with species-specific evolved life history affinities to sea ice. Although these hypotheses are not mutually exclusive, current evidence in the PAL region tends to favor the latter over the former. Since the inception of PAL, Adélie penguin populations have effectively collapsed, while those of gentoo and chinstrap penguins have increased dramatically, trends that are spatially and temporally coherent with decreasing regional sea ice duration. Adélie penguins are an ice-obligate polar species whose life history is intimately linked to the presence of sea ice, while chinstrap and gentoo penguins are ice-intolerant species whose life histories evolved in the sub-Antarctic, where sea ice is a less permanent feature of the marine ecosystem. In contrast, although krill constitute the most important component of the summer diets by mass of these three penguin species, changes in PAL krill abundances have exhibited no long-term trends, and thus fail to explain the divergent patterns in penguin populations evident in our time series. The PAL study region includes five main islands on which Adélie penguin colonies have historically occurred, and typically during the first week of January when chicks are in the guard stage (thus visible because they are no longer being brooded), these colonies are censused to determine the ratio of 1-chick to 2-chick nests. This census is restricted to nests that are no more than one meter in from the colony perimeter, and therefore tend to be more vulnerable to predation and other factors such as snow deposition that tend to affect the more marginal sectors of the colonies. The 1:2 chick ratio is thus highly sensitive to perturbations that are not necessarily evident in more optimal breeding habitats, and has provided important insights on the effects that breeding landscape quality has on reproductive success.