Survival and fidelity of translocated and resident burrowing owls in Arizona

Given the rapid pace of urbanization, mitigation translocations are increasingly being used to reduce human-wildlife conflicts, especially to move animals out of the path of land development. Burrowing owls (Athene cunicularia) are commonly subjected to translocations because of their association with flat, open lands that are attractive to development. But outcomes of burrowing owl translocations and the effects they have on their demographic parameters are seldom documented. From 2017-2019, we tracked the fates of 42 resident (non-translocated) burrowing owls and 43 translocated owls using very high frequency radio-telemetry across 4 release sites in southcentral Arizona, USA. Translocations were conducted by Wild At Heart (WAH), a non-profit raptor rehabilitation program, and owls were moved from areas with planned development activities to release sites that contained artificial burrows. Each year, WAH held translocated owls in groups of 6-10 owls with varying male to female ratios in aviaries prior to taking the owls to release sites where the owls stayed in soft-release tents for an acclimation period of 30 days before release. Resident owls were located at or near the 4 release sites. We used the joint live encounter and dead recovery model to evaluate differences in survival and fidelity probabilities between resident (non-translocated) and translocated burrowing owls and to assess factors that influenced these probabilities including sex, year, site, captivity duration, and the number of males in release cohorts for translocated owls. Annual survival was consistently lower for translocated owls (0.35, 95% CI = 0.10, 0.61 and 0.01, 95% CI = 0.00, 0.03 for 2017 and 2018, respectively) compared to resident owls (0.68, 95% CI = 0.45, 0.92 and 0.69, 95% CI = 0.47, 0.90 for 2017 and 2018, respectively). Annual fidelity was lower for translocated owls (0.05, 95% CI = 0.00, 0.15) compared to resident owls (0.79, 95% CI = 0.57, 1.00) in 2018, but fidelity did not differ significantly between translocated (0.54, 95% CI = 0.19, 0.89) and resident owls (0.62, 95% CI = 0.37, 0.87) in 2017. For translocated owls, the number of males in release cohorts negatively affected survival (beta $\hat{{\rm{\beta }}}$ = -0.74, 95% CI = -1.07, -0.40) and fidelity (beta $\hat{{\rm{\beta }}}$ = -0.73, 95% CI = -1.17, -0.29). Our results indicate the need for substantial changes to the current translocation methodology for burrowing owls in Arizona. Breeding season releases that included owl groups and multiple males within cohorts resulted in agonistic interactions, high mortality, and low fidelity. Translocations of this territorial species should be restricted to male-female pairs or single individuals. Earlier releases may allow owls time to become established on release sites prior to the breeding season, which could promote fidelity. We recommend these changes be implemented and evaluated along with an examination of other release methods.

Automated summary

This study tracked the fates of translocated and resident burrowing owls in Arizona and found that translocations resulted in lower survival and fidelity probabilities, especially when there were more males in the released cohorts. Therefore, significant changes to the current translocation methodology for burrowing owls are needed, restricting translocations to male-female pairs or single individuals.