Abstract
We developed an automated method using depth and one axis of body acceleration data recorded by animal-borne data loggers to identify activities of penguins over long-term deployments. Using this technique, we evaluated the activity time budget of emperor penguins (n = 10) both in water and on sea ice during foraging trips in chick-rearing season. During the foraging trips, emperor penguins alternated dive bouts (4.8±4.5 h) and rest periods on sea ice (2.5±2.3 h). After recorder deployment and release near the colony, the birds spent 17.9±8.4% of their time traveling until they reached the ice edge. Once at the ice edge, they stayed there more than 4 hours before the first dive. After the first dive, the mean proportions of time spent on the ice and in water were 30.8±7.4% and 69.2±7.4%, respectively. When in the water, they spent 67.9±3.1% of time making dives deeper than 5 m. Dive activity had no typical diurnal pattern for individual birds. While in the water between dives, the birds had short resting periods (1.2±1.7 min) and periods of swimming at depths shallower than 5 m (0.25±0.38 min). When the birds were on the ice, they primarily used time for resting (90.3±4.1% of time) and spent only 9.7±4.1% of time traveling. Thus, it appears that, during foraging trips at sea, emperor penguins traveled during dives >5 m depth, and that sea ice was primarily used for resting. Sea ice probably provides refuge from natural predators such as leopard seals. We also suggest that 24 hours of sunlight and the cycling of dive bouts with short rest periods on sea ice allow emperor penguins to dive continuously throughout the day during foraging trips to sea.
Highlights
Penguins are widely distributed around the Southern Ocean, and they are important consumers in the marine ecosystem [1]
Our results showed that emperor penguins made repeated dive bouts and rest periods on sea ice over a prolonged period
It is known that emperor penguins perform repeated dive bouts during foraging trips at sea [14], the detailed activity of each individual during a trip, especially when they are on the ice, has not been reported previously
Summary
Penguins are widely distributed around the Southern Ocean, and they are important consumers in the marine ecosystem [1]. Climate warming in the Antarctic region causes retreat of glaciers, collapse of large ice shelves, and reduction of sea ice [3,4,5,6], which affect breeding population sizes and distribution ranges of penguins [2,7,8].Specific responses of penguins to climate changes varied among species, due to variability of adaptation of species to the environmental conditions. The ice-intolerant species such as Gentoo penguins (Pygoscelis papua) have increased in number and expanded their range southward, while the ice-dependent species such as Adelie penguins (Pygoscelis adeliae) has decreased at almost all locations on the Antarctic Peninsula and contracted their distributional range poleward [2,7,9]. Sea-ice condition affects the penguin populations, the relationship between the foraging behavior of penguins and sea-ice condition is not clear, due to difficulties of tracking behavior at sea and on sea ice
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