Brood translocation increases post-release recruitment and promotes population restoration of Centrocercus urophasianus (Greater Sage-Grouse)

Abstract

Wildlife managers translocate Centrocercus urophasianus (Greater Sage-Grouse) to augment small populations, but translocated C. urophasianus often fail to reproduce post-release, hampering conservation objectives. We performed 2 C. urophasianus translocations in California and North Dakota from 2017 to 2020 using 2 methods at both sites: an established method of translocating females prior to nesting (i.e., a pre-nesting translocation), and a novel method wherein females were translocated with chicks after successfully hatching nests in source populations (i.e., a brood translocation). We radio-marked and monitored 135 translocated females and 284 source population females and used count data from leks in recipient and source populations to evaluate each method. Using an integrated population model (IPM), we estimated demographic parameters, including recruitment, by females translocated with each method. We estimated the finite rate of change in abundance (λ) in recipient and source populations given multiple simulated translocation strategies using each method and evaluated them using a cost-benefit metric (i.e., a ratio of the simulated change in abundance at recipient and source sites). We found that recruitment in recipient populations was substantially higher when brood translocations were employed compared to when pre-nesting translocations were employed. Most females translocated pre-nesting forewent reproduction entirely, whereas most females translocated with their broods successfully reared offspring in recipient populations. A per-capita comparison revealed that brood translocations resulted in λ that were 11–30% greater than pre-nesting translocations, but also revealed that the removal of brood-rearing females from source populations resulted in larger reductions in λ when compared with pre-nesting translocations. However, reductions in λ were small and the estimated cost-benefit metrics indicated that translocation of females with broods was a more effective method at spurring growth in recipient populations while minimizing impacts to source populations.