Assessing release strategies for reintroductions of endangered Wyoming toads

Abstract

We performed 3 experimental reintroductions of the critically endangered Wyoming toad (Anaxyrus baxteri) to study the toad's spatial ecology, behavior, and test the effectiveness of a soft-release strategy at Mortenson Lake National Wildlife Refuge, Wyoming, USA. We tracked reintroduced, captive-bred toads (n = 46) and field collected toads that had been in the wild for at least one year (n = 12) using a harmonic tracking system totaling 1,438 toad relocations in 2014 and 2015. We compared the spatial ecology and behavior of soft-released toads, hard-released toads, and overwintered toads. Hard-released toads were transported to the reintroduction site and released. Soft-released toads were kept in an outdoor enclosure at the release site for 14 days before release. Compared to hard-released toads, the soft-release group's average total path distance moved was lower (mean difference = 263.23, CI = 115.37 – 411.05, P = 0.007). Additionally, hard-released toads in the first 2 days post release moved 380% farther than the soft-released toads in the same 2-day period. Our results indicated that soft-releases are an effective way to improve site fidelity and retain wild-type spatial ecology and behavior of reintroduced captive-bred amphibians.