Matches and mismatches: ocean climate, prey phenology and breeding success in a zooplanktivorous seabird

In the marine environment, climatic changes are asymmetrically altering the phenologies of species at different trophic levels, causing an increase in the severity of mismatching between predators and their prey. At Triangle Island (British Columbia, Canada), the zooplanktivorous seabird Cassin’s auklet Ptychoramphus aleuticus breeds less successfully in warm-water years than in coldwater years. Previous researchers hypothesized that this occurred because, in warm years, there is less temporal overlap between the auklets’ nestling-provisioning period and the period when the copepod Neocalanus cristatus, an important prey item, is available to the birds in near-surface waters. I tested this hypothesis with data collected between 1996 and 2006. As predicted by the match-mismatch hypothesis, the copepods became scarce in nestling diets 2 to 3 wk earlier in warmer than in colder years, and were less prevalent overall in warm years. The auklets’ offspring were more likely to survive from hatching to fledging, and were heavier in mass at fledging, in years in which their diets were richer in N. cristatus. Information-theoretic approaches indicated that this effect of diet, a direct consequence of spring ocean temperature, outweighed other indirect influences of ocean temperature on offspring performance. Comparison with independent data on the timing and magnitude of local annual zooplankton biomass peaks indicated that prey timing, rather than prey abundance, was the key factor determining seasonal prevalence of the copepod in nestling diets. This study adds to a growing body of evidence showing that climate-driven phenological mismatches can alter critical trophic interactions, with potentially deleterious demographic consequences for predators.