Feeding Performance and Foraging Area of the Red-Legged Cormorant

Abstract

The foraging behavior and feeding locations of the Red-legged Cormorant (Phalacrocorax gaimardi) were studied at Ria Deseado, Argentina during the last week of the incubation period in 1999. VHF radio-transmitters were deployed on six nesting adult cormorants. Red-legged Cormorants fed during the daylight hours and made 4.0 ± 0.8 trips per day, with a mean duration of 1.2 ± 0.8 h. Birds spent 27% of daylight hours away from the colony on feeding trips, diving for 96% of the foraging trip, and made a mean of 78 dives per trip. Mean foraging range was 1.9 ± 0.9 km, being the shortest of any of the Patagonian cormorant species. Red-legged Cormorants fed mainly in shallow waters <5 m deep and within one km from the shore. Most of the feeding trips were undertaken during falling tide, when the birds performed the shortest feeding trips with maximum diving rates and, probably minimized transit times and maximized searching time on the seafloor. Our results show that foraging behavior is mainly influenced by environmental factors such as the direction of the tide. Red-legged Cormorants seems able to forage by selecting the appropriated tidal conditions to minimize foraging effort.