Publication Date

Summer 2014

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


James Harvey


Cerorhinca monocerata, forage fish, marine birds, Pacific saury, seabird foraging, stable isotopes

Subject Areas

Zoology; Wildlife conservation; Biology


We used stable isotopes (δ15N and δ13C) and conventional chick-diet sampling methods to evaluate seasonal shifts in diets of adult male and female rhinoceros auklets (Cerorhinca monocerata) and prey provided to chicks by each sex in California during 2012-2013. Rhinoceros auklet isotope values underwent similar shifts in both years, which differed in environmental and prey conditions. Mixing models indicated that northern anchovy (Engraulis mordax) were important prey for adults during fall/winter and juvenile rockfish spp. were important prey during incubation in both years. Adult trophic level increased between the incubation and chick-rearing periods, and mixing models indicated that adults likely ate similar prey species as those fed to chicks during both years. δ15N and δ13C of males and females were similar (P = > 0.05) during most seasons. During the 2012 chick-rearing period, however, adult female diet and meals delivered to chicks by females contained more Pacific saury (Cololabis saira) and less market squid (Doryteuthis opalescens) than male diet and meals delivered to chicks by males. Chick growth and survival to fledging were less during 2012 than during 2013, likely because chicks were fed lesser quality prey or fed less frequently in 2012. Lesser body condition of females but not males during incubation in 2012 indicated that sex-specific diet and chick provisioning differences during the 2012 chick-rearing period may have been related to energetic constraints on females.