Prey Switching and Variable Foraging Strategies of Black-Legged Kittiwakes and the Effect on Reproductive Success

Abstract

We studied the diets, foraging strategies, and reproduction of Black-legged Kittiwakes (Rissa tridactyla) during five years at two colonies within Prince William Sound, Alaska. Years with reduced occurrence of 1-year-old Pacific herring (Clupea pallasi) in kittiwake diets were associated with increased foraging trip duration, distance, and travel time at both colonies. Foraging range was consistently greater at the large, fjord colony with an annual mean trip duration of 4 hr and mean distance to the farthest feeding location of 40 km in years when 1-year-old herring dominated diets; these numbers increased to a maximum mean of 6 hr and 60 km during a year when kittiwakes consumed primarily young-of-year (YOY) herring and Pacific sand lance (Ammodytes hexapterus). Foraging trips of kittiwakes at the small, island colony averaged 2 hr and 5 km during years when 1-year-old herring dominated diets and increased when capelin (Mallotus villosus) and YOY herring and sand lance were consumed. Consequences of reduced herring availability were greatest at the large colony where alternative prey was limited, resulting in reduced reproductive success. In contrast, kittiwakes from the small colony were able to compensate for reduced herring availability by obtaining sand lance and capelin in relatively close proximity, and maintained above average reproductive success. Time spent traveling and trip distance increased with greater trip duration. However, search and prey capture times were only weakly related to trip duration and may reflect foraging strategies that vary with different species, age classes, or availability of prey consumed.