Building a new burrowing owl subpopulation through collaboration and translocation

Abstract

The western burrowing owl (BUOW, Athene cunicularia hypugaea)–a California species of special concern–has experienced range-wide declines, including in San Diego County where only one breeding population remained by the 2010s. As such, local conservation goals include increasing the number of breeding sub-populations to guard against extirpation of BUOW from the county. A working group including government agencies, non-profit organizations, and biological consultants was created to carry out adaptive management and conservation planning in support of these goals. Through a systematic and collaborative effort, we identified Rancho Jamul Ecological Reserve (RJER) as the first site for expanding the BUOW population. Site preparation techniques included vegetation management, targeted enhancement of the California ground squirrel (Otospermophilus beecheyi) population, and retrofitting/installation of artificial burrows. Population viability analysis utilizing 3 years of local demographic data predicted positive population growth from a small initial translocation population, and in 2018, we began translocating BUOW to RJER using a soft-release technique. Over three successive breeding seasons, we documented reproduction and retention of translocated owls, recruitment of their offspring, and recruitment of non-translocated owls. Here, we detail our methodologies and success metrics, and discuss leveraging our collaborative efforts to achieve conservation goals with limited resources.