Publication Date

Fall 2018

Degree Type


Degree Name

Master of Science (MS)


Moss Landing Marine Laboratories


Birgitte I. McDonald


apex predator, California Current System, common murre, diet, foraging effort, reproduction

Subject Areas

Ecology; Wildlife conservation; Wildlife management


Common Murre (Uria aalge) are the most abundant avian apex predator nesting in the California Current System (CCS) and nesting is the most energetically demanding phase of their lifecycle. The preyscape within flight distance of their nesting colony determines whether murres produce young, how hard they must work to do so, and what prey types are available to them. This study characterized the reproductive performance, foraging effort, and prey composition of murres nesting at a previously unstudied and large nesting colony in the CCS, Castle Rock National Wildlife Refuge, over an 11-year period (2007 - 2017) intended to capture a representative range of prey conditions. Timing of upwelling, coincident with seasonal increase in prey, accounted for 70% of the variability in nest initiation by murres. Reproductive success averaged 61% and, even in the most successful years, murres approached their behavioral limit to increase foraging effort and obtain adequate prey; crossing this threshold resulted in chicks being left unattended and widespread nest failure in 3 study years (2007, 2016, and 2017). Smelt and rockfish dominated the diet in good years and anchovy dominated in bad years. Prey available to murres nesting at this large colony closely matched the amount of prey required for them to produce young and, based on current conditions, even small shifts causing demand to exceed availability could result in large-scale reproductive failure of murres as well as other seabirds nesting here.