Release strategies and ecological factors influence mitigation translocation outcomes for burrowing owls: a comparative evaluation

Abstract

Mitigation translocations are increasing and if they are to fulfill their regulatory intent, the application of best‐practice principles to release strategy and monitoring is required. With an investment of 3 years, we engaged with stakeholders, including developers, to improve outcomes from mitigation translocations of an at‐risk species, the western burrowing owl Athene cunicularia hypugaea (BUOW). We evaluated the consequences of two primary translocation methods, displacement (i.e. exclusion from burrow) and translocation, against control owls, using a suite of success metrics focused on dispersal, survival and reproduction. We also tested the provision of visual and acoustic conspecific cues to dampen dispersal away from release sites. Within the displaced group, BUOW settled closer to the origin site if burrows were available nearby. Although translocated BUOW dispersed farther from the release site than displaced BUOW, this difference disappeared when conspecific cues were present. BUOW were 20 times more likely to settle at the release site when conspecifics or their cues were present. Translocating animals over longer distances (>17.5 km) reduced the incidence of BUOW returning to the origin site. When avoiding direct impacts to BUOW is not feasible, a determination of the most beneficial translocation method must be made, driven by site‐specific conditions and the 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. Mitigation translocations can benefit from carefully devised and tested hypotheses to determine what works and what does not; we advocate the increased use of evidence in mitigation translocation to guide management decisions and policies.

Survival and fidelity of translocated and resident burrowing owls in Arizona

“…Translocated sage‐grouse had shorter daily movements in their second year after release compared to the first year, which corresponded with increased survivorship (Ebenhoch et al 2019). In California, translocated burrowing owls had larger dispersal distances compared to resident owls and the use of conspecific cues reduced dispersal distance of translocated owls (Hennessy et al 2022). Although homing (the return to capture locations) is common among translocated raptors (Phillips et al 1991, Schafer et al 2002, Pullins et al 2018), only one owl in our study returned near its capture site.…”

“…In contrast, translocations conducted to mitigate impacts caused by urban and suburban land development have not been widely evaluated. Mitigation translocations of burrowing owls have used passive and active release techniques (Nguyen and Gardner 2017, Wisinski et al 2019, Hennessy et al 2022). Passive releases entail evicting owls from occupied burrows in development areas and collapsing their burrows, forcing the owls to disperse on their own (Trulio 1995, Feeney 1997, Nguyen and Gardner 2017).…”

Nest survival and productivity of translocated and resident burrowing owls in Arizona

“…Although the owls sometimes nest at higher densities in human‐altered environments (Millsap and Bear 2000, DeSante et al 2004, Rosenberg and Haley 2004), they are often disturbed by ground‐disturbing activities in these areas (Brown 2001, Klute et al 2003). Mitigation translocation is a management tool increasingly used to relocate animals, like the burrowing owl, that are directly affected by urban and suburban development (International Union for Conservation of Nature [IUCN] 2013, Germano et al 2015, Moehrenschlager and Lloyd 2016, Hennessy et al 2022). Despite the increased use of translocations, these programs often fail to establish self‐sustaining populations because of high mortality and low reproductive success (Fischer and Lindenmayer 2000, Germano et al 2015).…”

“…Passively displaced owls in California, USA, readily moved into artificial burrows created near their original burrows (Trulio 1995). In another California study, owls that were relocated using active and passive techniques settled near release sites (Hennessy et al 2022). Passive displacement appears to be effective when sufficient adjacent habitat makes it plausible for owls to relocate short distances (i.e., 100–600 m; Trulio 1995, Hennessy et al 2022), but its effectiveness is untested in situations where owls must move >600 m to find suitable habitat.…”

“…In another California study, owls that were relocated using active and passive techniques settled near release sites (Hennessy et al 2022). Passive displacement appears to be effective when sufficient adjacent habitat makes it plausible for owls to relocate short distances (i.e., 100–600 m; Trulio 1995, Hennessy et al 2022), but its effectiveness is untested in situations where owls must move >600 m to find suitable habitat. Conversely, active translocations aim to move owls to a new location away from their sites impacted by development.…”