Publication Date

Fall 2013

Degree Type


Degree Name

Master of Science (MS)


Environmental Studies


Lynne Trulio


alarm calls, behavior, Burrowing Owl, California Ground Squirrel, conservation, predation

Subject Areas

Animal behavior; Wildlife conservation; Conservation biology


Western burrowing owls are found in ground squirrel burrows throughout the urbanized landscape of the South San Francisco bay area, where they are threatened by habitat loss and degradation, prey limitation and predation. Previous research has characterized effects of habitat loss and prey-base limitations on owls, but the interplay between ground squirrels, owls and their predators has not yet been studied. The objective of this study was to assess the rate and types of predation interactions faced by Western burrowing owls and the extent to which California ground squirrels help burrowing owls reduce risk through alarm calling at Moffett Federal Airfield in northern Santa Clara County, California. From June through August 2012 and April through June 2013, over 100 hours of direct observations and 14,540 hours of camera trapping observations yielded seven owl takes by species including red-tailed hawk, red fox, striped skunk, common raven, and snake species. Although the ratio of squirrels to owls was 74:26, ground squirrels were observed responding to predator approaches before owls 58.8% of the time, while burrowing owls responded first 28.4% of the time. Burrowing owls reacted to 65.5% of squirrel alarm calls, while squirrels responded to only 25.8% of owl alarms. This research suggests healthy ground squirrel populations may provide important predator-avoidance services in burrowing owl habitat, and that predation should be of greater concern to burrowing owl conservation. And ground squirrels are needed to determine the extent of predation protection via alarm calls.