Prey switching and variable foraging strategies of Black-legged Kittiwakesand the effect on reproductive success

We studied the diets, foraging strategies, and reproduction of Black-legged Kittiwakes (Rissa tridactyla) during five years at two colonies within Pri nce William Sound, Alaska. Years with reduced occurrence of 1-year-old Paci fic herring (Clupea pallasi) in kittiwake diets were associated with increa sed foraging trip duration, distance, and travel time at both colonies. For aging range was consistently greater at the large, fjord colony with an ann ual mean trip duration of 4 hr and mean distance to the farthest feeding lo cation of 40 Irm in years when I-year-old herring dominated diets; these nu mbers increased to a maximum mean of 6 hr and 60 km during a year when kitt iwakes consumed primarily young-of-year (YOY) herring and Pacific sand lanc e (Ammodytes hexapterus). Foraging trips of kittiwakes at the small, island colony averaged 2 hr and 5 km during years when 1-year-old herring dominat ed diets and increased when capelin (Mallotus villosus) and YOY herring and sand lance were consumed. Consequences of reduced herring availability wer e greatest at the large colony where alternative prey was limited, resultin g in reduced reproductive success. In contrast, kittiwakes from the small c olony 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 incre ased with greater trip duration. However, search and prey capture times wer e only weakly related to trip duration and may reflect foraging strategies that vary with different species, age classes, or availability of prey cons umed.