Natal Dispersal Distance of Golden Eagles in the Southwestern United States

Abstract

Abstract Data on natal dispersal distances (NDDs) of golden eagle Aquila chrysaetos in North America are needed to define local area populations and inform decisions authorizing take (i.e., injury, death, or disturbance) of the species via federal permit. Sixteen golden eagles (6 males, 10 females) tagged with satellite transmitters as ∼8-wk-old nestlings in the southwestern United States during 2010–2013 dispersed a mean of 55.3 km (SD = 29.7, median = 64.5), either 1) between their natal nest sites and nests where they first bred (n = 3 females, all subadults, i.e., in their fourth year of life), or 2) between natal sites and where they permanently settled as adults at least in their fifth year of life, but did not necessarily breed (i.e., exhibiting only gross natal dispersal). On average, females dispersed about 50% farther than males; mean NDD of males and females was 41.2 km (90% credible interval = 11.1–75.2) and 63.8 km (44.8–82.6), respectively. Median NDD of males and females was 41.5 and 65.8 km, respectively; in a Bayesian framework, the estimated difference in posterior median distributions of male and female NDDs was 22.2 km (−15.7 to 57.3; P ≠ 0 = 0.89), tentatively indicating that NDD of golden eagles in our study area may be female biased. Although our findings are based on a relatively small data set including both effective and gross natal dispersal records, they represent the first comparison of NDD between sexes of golden eagle in North America and the first published records on the continent of the species' NDD based on telemetry methods. More work is needed to validate whether golden eagle NDD in at least some regions of North America is female biased, which could have important implications for authorizing take of the species.