Comparing population vital rates of resident and translocated Greater sage-grouse of the Yakima Training Center, Yakima, WA

Kyle Gregory Ebenhoch

As translocations become increasingly valuable and common in conservation efforts, understanding factors that influence the demography of translocated animals continues to be a focus of wildlife research. One species that has received much attention for translocation is the Greater sage-grouse (Centrocercus urophasianus). The Yakima Training Center (YTC) near Yakima, Washington contains the least genetically diverse population across the species' range, and has been a site of recent translocation releases. We compared demographic rates of sage-grouse translocated to YTC to that of resident birds. Because newly translocated birds experience physiological stress during the translocation process and are released in unfamiliar habitat, we expected their demographic rates to differ from residents. We analyzed very high frequency (VHF) location data of resident and translocated sage-grouse from 1989-1993, 1999-2001, 2004-2007, and 2012-2017 to determine movement rates, survival, and productivity. Newly translocated sage-grouse had larger daily movements (0.64 km/day) and smaller 95% home ranges (88.18 km2) than residents and previously translocated birds. Comparing different measures of movement in Cox proportional hazard survival models, we showed that movement did not influence survival rates. Furthermore, log-rank tests demonstrated that annual survival rates were similar among residency status categories. Newly translocated birds initiated nests less often (34.5%) than residents (59.6%); however, these rates were similar to residents after their first year. Nest initiation date was the most important predictor of nest survival, with nests initiated later in the season having higher probabilities of surviving. One reason for this pattern may have been the abundance of other ground nesting bird species on YTC with similar breeding and nesting times that may have dispersed predation efforts, thereby reducing the risk for sagegrouse nests. Nonetheless, nest survival rates did not differ among residency status categories. Our results indicate that translocated sage-grouse exhibit a short-term decline in demographic rates in their first year but align to that of resident birds in subsequent years. Similarities in adult survival and nest survival among residency status categories, respectively, further indicate that YTC is a viable translocation release site. However, continued declines in population size indicate that recent translocation efforts have not improved population viability.

Comparing population vital rates of resident and translocated Greater sage-grouse of the Yakima Training Center, Yakima, WA

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