Adelie penguin chick fledging weights, 1991-2021

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. Adélie penguin chick fledging weights are obtained every two days (or as ice and weather conditions permit) at three beaches on Humble Island beginning when the first fledglings appear on any one of these beaches, and continuing until the last fledglings depart. These data are generally collected during the first three weeks of February by first censusing the total number of chicks present on each beach, and then sub-sampling 30% of the censused population. The metric of interest is the weight (in grams) of individual chicks, which is an important predictor of overwinter survival and thus future recruitment into the population as breeding adults. Dr. Megan Cimino took over as PI of the LTER seabird project in 2020 from Dr. William Fraser. Field data collection between 2020-2022 has remained consistent with previous years. No data collected during the 2021-2022 season due to the Palmer Station Pier Build.