Mitigation translocations are increasing and if they are to fulfill their regulatory intent, the application of scientific best-practice principles to release strategy and monitoring is required. With an investment of 3 years, we engaged with various stakeholders, including developers, to implement a scientific framework around mitigation translocations of an at-risk species, the western burrowing owl (Athene cunicularia hypugaea, BUOW), which is vulnerable due to declining population numbers and loss of habitat. To improve mitigation strategies, we evaluated the consequences of two relocation methods (burrow displacement and active translocation) against a control group using a broad suite of metrics (dispersal, mortality, and reproduction). We also tested the provision of visual and acoustic conspecific cues to anchor owls to release sites. The incorporation of satellite telemetry and field monitoring techniques allowed longer monitoring of the species than is generally either performed or required after relocation. Beginning in January 2017, 54 relocated and control BUOW were tracked across four counties in Southern California. In addition, we surveyed habitat conditions at original owl burrow sites, the release sites, and sites where the owls ultimately settled, including terrain, climate, vegetation, and the density of available burrows.
Results/Conclusions
Although actively translocated BUOW dispersed farther from the release site than BUOW displaced from their burrow, this difference disappeared when conspecific cues were present. In fact, BUOW were ~20 times more likely to settle at the release site when conspecifics or their cues were present. Within the burrow-displaced group, BUOW settled closer to the eviction site if burrows were available nearby. Resettlement without loss of an established home range was associated with high survival after 6 months (100%, n=16). However, burrow-displaced BUOW often ended up in lower-quality habitat than experienced at their original burrow, indicating that the availability of highly suitable habitat may be a limiting factor. Dampening dispersal may have facilitated breeding, as indicated by an inverse relationship with dispersal distance (n=32, p<0.01, R2=0.55). When avoiding direct impacts to BUOW is not feasible, a determination of the most beneficial relocation method must be made, driven by site-specific conditions and feasibility of implementing best management practices. The known costs of translocation to survival may be offset by long-term advantages such as the establishment of breeding populations inside protected areas. Adoption of experimental approaches to mitigation translocation such as the one presented here should become more routine to achieve conservation goals.