Spatiotemporal Variability in the Diet of Nonbreeding Brandt's Cormorant (Phalacrocorax penicillatus) in the Monterey Bay Region

Abstract

Brandt's Cormorant (Phalacrocorax penicillatus) diet composition was investigated using pellets (n = 285) collected on 19 sampling days at 3 locations during the 2006-07 and 2007-08 nonbreeding seasons in the Monterey Bay region. The conventional diet method was used, and the efficacy of the all-structure technique was evaluated. Although 29 species were consumed, Northern Anchovy (Engraulis mordax) dominated the diet and Speckled Sanddab (Citharichthys stigmaeus) also was important. Few rockfishes (Sebastes spp.) and Market Squid (Doryteuthis opalescens) were consumed compared with the number consumed in previous studies in the region during the 1970s. El Niño and La Niña conditions during the study provided a unique opportunity to examine predator response. Greatest prey number and diversity occurred at locations within Monterey Bay during cooler ocean conditions, whereas the outer coast location remained unchanged. Short-term specialization was observed, but mean prey diversity indicated a generalist feeding mode. Patterns of prey number and diversity within a nonbreeding season were not consistent among locations. This study demonstrated the importance of periodic sampling at multiple locations within a region to detect spatiotemporal variability in the diet of this opportunistic generalist.