Sex and individual differences in foraging behavior of Japanese cormorants in years of different prey availability |
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Authors: | Koji Ishikawa Yutaka Watanuki |
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Institution: | (1) Laboratory of Animal Ecology, Graduate School of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo 060–8589, Japan, |
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Abstract: | Japanese cormorants, Phalacrocorax capillatus, are sexually dimorphic seabirds with males that are heavier and that dive deeper than females. Sex differences in prey composition
and foraging behavior of those rearing chicks at Teuri Island, Hokkaido, were examined by collecting food-loads from parents
in 1992–1998 and by radio-tracking ten birds each in 1997 and 1998 when prey availability was different. Males fed more on
benthic and epibenthic fishes (82% mass) than did females (34%) while females fed more on epipelagic and coastal fishes (53%)
than did males (18%). Males made longer dives (53 s) at feeding sites closer to the island (7 km) than females (39 s, 13 km)
in 1997. In 1998 when the availability of epipelagic fish seemed to be higher, there were no sex differences in dive duration
and distance to the feeding sites (35 s and 9 km for males, 36 s and 10 km for females). This sex difference in foraging behavior
with a poor availability of epipelagic fish suggests that high diving ability possibly enables males to feed on demersal fish.
Birds specializing in coastal shallow waters around the island made long dives; hence they were probably foraging in bottom
layers. Those foraging in deeper shelf waters made short dives and they were thought to forage in surface layers.
Electronic Publication |
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Keywords: | Cormorants Diet Diving ability Epipelagic Demersal Prey variability Sexual dimorphism |
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