Climate change and the population biology of common murres and other seabirds of the California Current marine ecosystem

I investigated the influence of physical and biological oceanographic processes on the biology of Common Murres Uria aalge and other seabirds in the California Current marine ecosystem. In the first chapter, we analyzed information on the Common Murre population at the South Farallon Islands. Whole-colony, sub-colony, and study plot data showed that population growth has been slow to moderate, averaging ∼5% per annum over the last decade. In chapter 2, I investigated demographic aspects of individual quality by studying repeatability in laying date of 37 marked female murres. Repeatability was estimated as 0.204 and was related to fitness. In chapter 3, I considered proximate and ultimate factors influencing timing of breeding of murres from 1972--1997. Mean breeding date became earlier through time even though ecological conditions appeared to deteriorate. Based on the probability of fledging young, there appeared to be directional selection for early breeding throughout most years of study, and stabilizing selection in 3 years corresponding to a period when mean breeding date also appeared to stabilize. In chapter 4, we used stable isotope analysis to determine seabird trophic relationships in the Gulf of the Farallones. Results suggest a shift in trophic level and diet between spring and summer from krill to fish for murres. In chapter 5, we studied the effects of low-frequency marine climate change on the reproductive performance of 11 species of marine bird from southern and central California, 1969--1997. Change in the birds' abilities to provision young during May--July each year appeared closely related to temporal changes in reproductive performance. Changes in diet, possibly related to ocean warming, are likely responsible for changes in performance in both oceanographic domains. Last, for chapter 6, we examined viability of Xantus' Murrelets Synthliboramphus hypoleucus on Santa Barbara Island, California. Chronically poor reproductive performance was found to be primarily responsible for population decline. Predation on eggs accounts for low estimates of productivity. Long-term changes in the California Current food web also may be directly or indirectly limiting the population of this rare marine bird.