Multilevel models reveal no cohort-level variation in time spent foraging to account for a collapse in kittiwake (Rissa tridactyla) breeding success

As central-place foragers, colonial seabirds should be able to compensate, up to some threshold, for changing breeding conditions by remaining flexible in the amount of time allocated to foraging versus other activities. Black-legged kittiwake (Rissa tridactyla) colonies in Chiniak Bay, Kodiak Island, Alaska experienced high productivity from 2001 to 2003 and virtually no productivity from 2004 to 2005. In the absence of disease epidemics, increased human disturbance or predation, we applied multilevel, mixed, regression models to assess the hypothesis that the collapse from high to low breeding success was due primarily to changes in prey availability. Under this hypothesis, we predicted that longer foraging trips would be associated with reduced breeding performance in cohorts of kittiwakes—groups marked with radio-transmitters at the same colony in the same year. We separately modeled two response variables: foraging trip-durations made during the incubation and early chick stages. Multilevel mixed models revealed only weak variation at the cohort-level in either response variable; hatching success and fledging success accounted for none or less than 2% of the total variation in trip-durations made during the incubation and early chick stages, respectively. The majority of the variation in our response variables was at the observation (ca. 80–90%) and bird (or individual) levels (ca. 10–12%). Our results expose the unreliability of using indirect evidence to implicate prey availability as the primary cause of widespread breeding failures in colonial seabirds. In the ecological literature, two types of inferences seem particularly vulnerable to indirect evidence: inferences following studies on species that are accepted or strongly promoted as bioindicators of changes in marine productivity such as the black-legged kittiwake, and inferences that implicate a fisheries-induced reduction in prey availability to failed breeding. In light of these pitfalls, we recommend that long-term monitoring studies on kittiwakes and other seabirds carefully consider in their study designs and implementations multiple working hypotheses that might explain major changes in breeding success.