Fitness costs of migration: Comparative demography of burrowing owls in North America
Burrowing owls (Athene cunicularia) in North America have suffered population declines in many areas and significant range contraction. Burrowing owls are considered endangered in Minnesota, Iowa, Mexico, and Canada, and populations have declined significantly in British Columbia, Alberta, Arizona, California, Colorado, Kansas, Nebraska, Nevada, New Mexico, Utah, and Washington. Many state wildlife agencies are becoming increasingly concerned about declining burrowing owl populations. Despite the widespread declines and increased concern for burrowing owl populations throughout North America, we lack reliable data on underlying causes of declines. Prior to developing and implementing recovery efforts, we need to understand the ultimate cause of population declines and the proximate factors influencing local distribution, reproductive success, and annual survival of burrowing owls. Anthropogenic changes to over-wintering areas in Mexico has been proposed as a possible cause of observed population declines. If reduction in habitat quality/quantity in Mexico is the primary cause of observed declines, we would expect migratory populations to have substantially lower annual survival compared to resident populations. Burrowing Owls are ideal for examining the cost associated with migration because populations vary in the extent to which they migrate; some populations are completely migratory, some are partially migratory, and some are completely resident. The goal of this project is to compare primary demographic parameters among populations of burrowing owls that vary in the extent to which individuals migrate. Coordinated research using standardized capture-banding-resighting methods will be conducted at 7 study sites in 4 western states. The 7 sites will include two sites at which owls are entirely migratory (central Washington and northeastern Wyoming), one site at which owls are about 50% migratory (southern Washington), and 4 sites at which owls are entirely non-migratory (southern Arizona and central and southern California). Project objectives include: 1) compare annual fecundity and annual territory fidelity among populations, 2) document migratory status of each local population, and 3) compare annual survival of adult owls (both males and females) among populations. Data from each study area will be pooled to examine how demographic parameters vary with extent of migratory tendency across populations.
