COS 105-2
Western burrowing owl predation in an urban setting in California: Do California ground squirrel calls reduce risk?
Western burrowing owls (Athene cunicularia hypugaea) use California ground squirrel burrows (Spermophilus beechyi) throughout the urbanized landscape of the South San Francisco Bay area for nesting and protection. In this urban setting, burrowing owls are threatened by habitat loss and degradation, prey limitation and increasing populations of urban predators. Previous research has characterized effects of habitat loss and prey-base limitations on owls, but no study has quantified the relationship between ground squirrels, owls and their predators. This study assessed the rate and types of predation interactions faced by burrowing owls and the extent to which California ground squirrels may help burrowing owls reduce risk through alarm calling. I collected data at Moffett Federal Airfield in northern Santa Clara County, California during two burrowing owl breeding seasons using phototrapping and direct observation of burrowing owls and ground squirrels near occupied owl burrows.
Results/Conclusions
From June through August 2012 and April through June 2013, I conducted over 100 hours of direct observations and collected 14,540 hours of camera trapping. These observations together yielded 7 owl takes by red-tailed hawk, red fox, striped skunk, common raven, and snake species. Although the ratio, by abundance, of squirrels to owls during direct observations was 74:26, ground squirrels were observed responding to predator approaches before owls only 58.4% of the time, while burrowing owls responded first 28.7% of the time. Burrowing owls reacted to 65.5% of squirrel alarm calls indicating that squirrel alarm calling was important to the owls. Squirrels, however, responded to only 25.8% of owl alarms. This research suggests that healthy ground squirrel populations may provide important predator-avoidance services to burrowing owls, especially in the face of increasing urban predator populations, such as corvids and red-tailed hawks.