Adelie penguin breeding population arrival chronology on Humble Island, 1991 - present.

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 arrival chronology of adult Adélie penguins on Humble Island is documented annually through island-wide censuses performed as ice and weather conditions permit. Recorded data (numbers of adults present) provide a measure of the number of adults arriving daily at the breeding colonies, a metric that is sensitive to environmental conditions such as sea ice extent during late winter and early spring. These data are also used in combination with other metrics to determine the optimal window for other, more extensive area-wide breeding population censuses (see CENSUS).

帕尔默长期生态研究计划（Palmer LTER, PAL）的海鸟研究组分的核心长期目标，是识别并阐明调控区域企鹅种群平均适合度（种群增长率）的机制性过程。本研究依托两项核心假说开展：其一认为种群平均适合度的最优解释因子为区域磷虾生物量的变化；其二提出海冰的长期变化会通过改变物种间的竞争天平——依据各物种演化出的、与海冰适配的生活史偏好——使某一物种相较另一物种更占优势，进而影响种群平均适合度。尽管两项假说并非互斥，但PAL区域的现有证据更倾向于支持后者。自PAL计划启动以来，阿德利企鹅（Adélie penguin）种群已发生实质性衰退，而巴布亚企鹅（gentoo penguin）与帽带企鹅（chinstrap penguin）种群则大幅增长，此类趋势与区域海冰存续时长缩短的时空特征高度吻合。阿德利企鹅为依赖海冰的极地物种，其生活史与海冰的存在紧密绑定；而帽带企鹅与巴布亚企鹅则为不耐海冰的物种，其生活史演化于海冰并非常年存在的亚南极海域。尽管磷虾是上述三种企鹅夏季日粮中以生物量计占比最高的组成部分，但PAL区域的磷虾丰度并未呈现长期变化趋势，因此无法解释本次时间序列中观测到的企鹅种群分化格局。研究人员会在海冰与天气条件允许的情况下，每年通过全岛普查记录成年阿德利企鹅抵达亨布尔岛（Humble Island）的时序。所记录的成体种群数量数据，可用于衡量每日抵达繁殖群落的成体规模，该指标对晚冬及早春的海冰范围等环境条件极为敏感。此类数据还会与其他指标结合，用于确定后续更大范围区域繁殖种群普查的最佳窗口期（详见CENSUS部分）。