Breeding Range Expansion of Sitta pusilla Latham (Brown-headed Nuthatch) in Virginia

摘要

Dispersal and establishment of new breeding populations of Sitta pusilla (Brown-headed Nuthatch) outside of its historic range in Virginia have been recorded since the 1960s. We systematically gathered published and unpublished occurrences of Brown-headed Nuthatches beyond their historic range in Virginia from 1966 to 2019 and evaluated local and landscape characteristics of sites in these areas. Brown-headed Nuthatches have expanded their distribution in Virginia into 29 counties, with breeding confirmed and/or sustained observations over more than 1 year recorded at 38 sites in 16 counties (26 sites in the Piedmont in 10 counties; 12 sites in the Ridge and Valley in 6 counties). The majority (25 of 38; 66%) of these new sites occupied by Brown-headed Nuthatches occur in semi-open recreational and residential areas, and the remaining 13 sites occur in areas broadly classified as forest. Pinus spp. (pines) are present at 37 of 38 occupied sites, most frequently P. virginiana (Virginia Pine) and P. strobus (Eastern White Pine), with an average canopy cover (all tree species) of 57% within a 250-m radius of each site. Pine-dominated forest represented a small percentage (1-24%) of land-cover types at a landscape scale (areas within a 5-km radius of occupied sites), not exceeding 4% in the Ridge and Valley region. Most colonization of these sites by Brown-headed Nuthatches in Virginia was not associated with the expansion of pine plantations, except for an apparent recent (2015-2018) association with P. taeda (Loblolly Pine) in the northern Piedmont. In the context of the current range expansion, we identify 3 management interventions (provision of nest boxes, management of Loblolly Pine plantations, restoration of P. echinata [Shortleaf Pine]) that could serve to provide suitable nesting habitat conditions for Brown-headed Nuthatches in Virginia.