Population Trajectory of Burrowing Owls (Athene cunicularia) in Eastern Washington

Anecdotal evidence suggests that burrowing owls have declined in Washington. The Washington Department of Fish and Wildlife is currently conducting a status review for burrowing owls which will help determine whether they should be listed as threatened or endangered in the state. To provide insights into the current status of burrowing owls (Athene cunicularia) , we analyzed data from the North American Breeding Bird Survey using two analytical approaches to determine their current population trajectory in eastern Washington. We used a one-sample t-test to examine whether trend estimates across all BBS routes in Washington differed from zero. We also used a mixed model analysis to estimate the rate of decline in number of burrowing owls detected between 1968 and 2005. The slope in number of burrowing owls detected was negative for 12 of the 16 BBS routes in Washington that have detected burrowing owls. Numbers of breeding burrowing owls detected in eastern Washington declined at a rate of 1.5% annually. We suggest that all BBS routes that have detected burrowing owls in past years in eastern Washington be surveyed annually and additional surveys conducted to track population trends of burrowing owls at finer spatial scales in eastern Washington. In the meantime, land management and regulatory agencies should ensure that publicly managed areas with breeding burrowing owls are not degraded and should implement education and outreach programs to promote protection of privately owned areas with breeding owls. Author to whom correspondence should be addressed. Email: [email protected] Introduction Burrowing owl (Athene cunicularia; Molina 1782) populations are thought to be declining in several portions of their breeding range in North America (Dechant et al. 1999, Wellicome and Holroyd 2001). Burrowing owls are listed as a “Species of National Conservation Concern” on the federal level and in every U.S. Fish and Wildlife Service Region in which they occur (U.S. Fish and Wildlife Service 2002). They are listed as endangered, threatened, or a species of concern in nine U.S. states (Klute et al. 2003). Washington Department of Fish and Wildlife is currently evaluating the status of burrowing owls, and this status review will be used by the Fish and Wildlife Commission to determine whether owls should be listed as threatened or endangered in Washington. Anecdotal evidence suggests that burrowing owls have declined in eastern Washington (Smith et al. 1997, Klute et al. 2003, Conway et al. 2005) and recent analysis (Sauer et al. 2005) of data from the U.S. Geological Survey’s (2006) North American Breeding Bird Survey (BBS) suggest that burrowing owl populations declined by 3.1% per year in Washington between 1968 and 2005, but this trend estimate was not significant (P = 0.78, n = 8). Sauer et al. (2005) rank the credibility of trend estimates for each bird species within each state, and the credibility of the trend estimate for burrowing owls in Washington was considered low. Previous authors have also suggested that burrowing owls are not sampled adequately by the BBS because owls typically have low breeding densities and are patchily distributed (Andelman and Stock 1994, Holroyd and Wellicome 1997). The ability to detect a significant trend for burrowing owls in Washington is compromised because the number of burrowing owls per route was very low (<0.1 birds per route) and the number of routes on which owls were detected was also low (n = 16). Sauer et al. (2005) controlled for variation in surveyor detection probability by estimating