Antarctic ecosystem

The foraging behavior of nonbreeding Adélie penguins in the western Antarctic Peninsula during the breeding season

Summary

This study followed Adélie penguins from King George Island during the 2016/2017 season to understand how nonbreeding penguins behave differently from those raising chicks. The researchers found that nonbreeding penguins have distinct preferences when foraging at sea. They sought out colder waters with more sea ice, especially in areas where Weddell Sea water flows along the Antarctic Peninsula coast. During the early breeding season when penguins were incubating eggs, both breeding and nonbreeding birds foraged in similar areas. However, as the season progressed to the crèche stage - when chicks are old enough to huddle together - clear differences emerged. Breeding penguins stayed close to their colonies to feed their chicks, while nonbreeding penguins made long journeys into the Weddell Sea as part of their premolt preparation. Despite this spatial segregation, both groups still used the central Bransfield Strait as an important shared foraging area, showing some overlap in their habitat use. The research reveals that breeding and nonbreeding penguins operate on different spatial and temporal scales, meaning they may respond differently to environmental changes. This has important implications for conservation planning - effective ecosystem-based management must consider the needs of penguins at all life history stages, not just breeding birds, to protect the full range of habitats these populations depend on.

This graph shows how far breeding (green) and nonbreeding (purple) Adélie penguins traveled from their King George Island colony over time. The vertical lines mark key breeding dates: hatching, crèche formation, and fledging. The histograms show data distribution - top shows daily location counts, side shows distance ranges in 10-km intervals. Both groups start close to the colony, but nonbreeding penguins travel much farther as the season progresses, especially after the crèche stage when breeders must stay near their chicks.

Key Findings

Nonbreeding Adélie penguins increased their prey search behavior in areas with lower sea surface temperatures, shallower depths, and higher sea ice concentration

Both breeders and nonbreeders transit through the deep Central Basin of the Bransfield Strait with high directional movement

Nonbreeders showed a bimodal movement pattern, with extended on-land residency periods between foraging trips

Spatial overlap between breeders and nonbreeders was highest during incubation, lowest during crèche stage

Nonbreeders departed on synchronized premolt foraging trips into the Weddell Sea during the crèche stage

The southern Bransfield Strait represents important foraging habitat for multiple krill-dependent predators

Abstract

Information on marine predator at-sea distributions is key to understanding ecosystem and community dynamics and an important component of spatial management frameworks that aim to identify regions important for conservation. Tracking data from seabirds are widely used to define priority areas for conservation, but such data are often restricted to the breeding population. This also applies to penguins in Antarctica, where identification of important habitat for nonbreeders has received limited attention. Nonbreeding penguins are expected to have larger foraging distributions than breeding conspecifics, which may alter their interactions with physical environmental factors, conspecifics, other marine predators, and threats. We studied the movement behavior of nonbreeding Adélie penguins tracked during the 2016/2017 breeding season at King George Island in the South Shetland Islands, Antarctica. We quantify how nonbreeding penguins' horizontal moment behavior varies in relation to environmental conditions and assess the extent of spatial overlap in the foraging ranges of nonbreeders and breeders, which were tracked over several years. Nonbreeders increased their prey search and area-restricted foraging behavior as sea surface temperature and bottom depths decreased, and in response to increasing sea ice concentration. Nonbreeders tended to transit (high directional movement) over the relatively deep Central Basin of the Bransfield Strait. The majority of foraging behavior occurred within the colder, Weddell Sea–sourced water of the Antarctic Coastal Current (incubation) and in the Weddell Sea (crèche). The utilization distributions of breeders and nonbreeders overlapped in the central Bransfield Strait. Spatial segregation was greater during the crèche stage of breeding compared to incubation and brood, because chick provisioning still constrained the foraging range of breeders to a scale of a few tens of kilometers, while nonbreeders commenced with premolt foraging trips into the Weddell Sea. Our results show that breeding and nonbreeding penguins may not be impacted similarly by local environmental variability, given that their spatial and temporal scales of foraging differ during some part of the austral summer. Our study highlights the need to account for different life history stages when characterizing foraging behavior of marine predator populations. This is particularly important for "sentinel" species monitored as part of marine conservation and ecosystem-based management programs.

Published in

Ecosphere

2022

Authors

Oosthuizen, W. Chris; Pistorius, Pierre A.; Korczak-Abshire, Malgorzata; Hinke, Jefferson T.; Santos, Mercedes; Lowther, Andrew D.

Institutions

Marine Apex Predator Research Unit, Institute for Coastal and Marine Research and Department of Zoology, Nelson Mandela University Centre for Statistics in Ecology, Environment and Conservation, University of Cape Town Institute of Biochemistry and Biophysics, Polish Academy of Sciences Antarctic Ecosystem Research Division, Southwest Fisheries Science Center, NOAA Departamento Biología de Predadores Tope, Instituto Antartico Argentino Norwegian Polar Institute

Methods

Biological sampling DataField

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