Pomarine jaeger preys on adult black-legged kittiwake

Abstract

On 5 June 1977, while on a cruise in the decomposing pack ice in the Bering Sea, we observed a light phase Pomarine Jaeger ( Stercorarius pomarinus ) attack, kill and feed on an adult Black-legged Kittiwake ( Rissa tridactyla ), 1 of approximately 10 individuals within 20 m of the ship's stern. We did not observe the birds until 1 min after the initial attack and do not know if the kittiwake was sitting or flying. No food was visible in the kittiwake's bill at the start of our observations nor was it observed regurgitating its stomach contents after the attack. During the first 5 min the kittiwake managed to become airborne a number of times but the jaeger maintained its hold and forced it back to the water. After 5 min the jaeger began to submerge the kittiwake's head, still holding it by the neck. Because of the kittiwake's struggling, the jaeger was unable to hold it under for more than 5 sec at a time. For the next 15 min it continued to submerge the victim's head, lift it out of the water, and then submerge it again. When it held the kittiwake under water, it kept both feet on its lower neck; this may have helped keep the head submerged. In the last 5 min of this activity, when the kittiwake offered little resistance, the jaeger occasionally used only its feet to push it under water. Other kittiwakes remained in the area, a few swimming within 2 m of the 2 birds. No attempt was made to mob the jaeger.