Habitat selection, nesting success and genetic structure of the American Three-toed Woodpecker (Picoides dorsalis) in the Black Hills of South Dakota

Isolated, low density and sedentary species face unique ecological and conservation challenges that common, contiguous populations may not experience. The American Three-toed Woodpecker population in the Black Hills of South Dakota is of particular conservation concern because of its geographic isolation from other populations and sedentary behavior which may increase its risk of extirpation. Because of this species close association with dense high elevation conifer forests and its unobstrusive behavior, basic ecological and genetic data are lacking. In this comprehensive study, I combine ecological data such as foraging, nesting and home range habitat selection along with population abundance estimates and genetic population structure data to determine the overall status of the American Three-toed Woodpecker population in the Black Hills of South Dakota. Relative abundance estimates from population surveys indicated 0.20 birds per census point in white spruce forests in the Black Hills. This estimate is roughly similar to other populations in the Rocky Mountains. To determine foraging preferences, I compared use of foraging substrates to substrate availability and found that the Black Hills population preferred large (> 23 cm dbh) living and dead spruce and large ponderosa pine trees and selected against living small spruce. Although the American Three-toed Woodpecker is known to exploit areas of recent disturbances such as post-burn habitats because of increased foraging opportunities, the Black Hills population was not present in areas of recent burns. Aspen appears to be an important characteristic for nest site selection as 61% of nests were located in aspens and nest sites had significantly more large living and snag aspens compared to random sites. In contrast to previous research, our results do not support the importance of conifer snags for nesting substrates. Nesting success estimates in this study were lower than those for other primary cavity nesting birds. Overall apparent nesting success was 42.9% and nest success estimates that account for when nests were found were even lower (Mayfield nest success = 13.0% and simple-model maximum-likelihood nest success estimate = 17.4%). Consistent with other nesting success studies focusing on cavity nesting birds, most nest failures were attributed to predation. The home range size was comparable to that of Eurasian Three-toed Woodpecker (Picoides tridactylus), but smaller than for other western conifer forest woodpecker species. Edge habitats such as roads appear to be important within home ranges and at a landscape scale. Black Hills American Three-toed Woodpeckers show high genetic variation in microsatellite loci and high haplotype diversity and low nucleotide diversity in mtDNA sequences. Overall, these results are indicative of a population bottleneck and subsequent range expansion with extremely limited recent gene flow between the Black Hills population and other populations. Because of the geographic isolation, natural history characteristics and limited amount of gene flow, the Black Hills population of American Three-toed Woodpeckers should be a priority in resource management planning.