Characteristics of pileated woodpecker ( Dryocopus pileatus) cavity trees and their patches on southeastern Vancouver Island, British Columbia, Canada

Abstract

Cavity trees and cavity patches (areas around cavity trees) used by pileated woodpeckers were located in Coastal Western Hemlock and Coastal Douglas-fir forest types on southeastern Vancouver Island during 1996 and 1997. Trees with active nests and with apparent pileated cavities ( n=28) were larger than trees without cavities ( n=200). Of the seven confirmed nest trees, three were grand fir ( Abies grandis), two were Douglas-fir ( Pseudotsuga menziesii) and two were red alder ( Alnus rubra). These nest trees had a mean diameter at breast height (dbh) of 82 cm (±16 S.E.), a mean height of 22.0 m (±5.2 S.E.), and 91% (±9 S.E.) of their bark remaining. Compared to non-cavity patches ( n=58), patches with nests or apparent pileated cavities ( n=18) were significantly lower in elevation and greater proportions were in the oldest successional stages, in mature and old forest structural stages, and in moderately disturbed areas. The proportion in young forests, however, was not different than that in non-cavity patches ( n=58). Cavity patches had greater proportions of bigleaf maple ( Acer macrophyllum) and grand fir, but less western hemlock ( Tsuga heterophylla) than patches without cavity trees. The mean diameter of nest trees used by pileated woodpeckers in North America ranges from 40 to 100 cm and varies with location, tree species, and forest characteristics, such as the availability of large dead trees. Although this broad range of diameters indicates flexibility in nest tree selection, in all published studies, pileated woodpeckers select the larger trees of those available, thus revealing consistent preferences for large-diameter trees for nesting. Management of forests to supply nesting habitat for pileated woodpeckers on southeastern Vancouver Island, must include retention of large live and dead trees, particularly grand fir, Douglas-fir and red alder. In addition, stands should be reserved that have greater proportions of bigleaf maple and grand fir (but less western hemlock) and that are at least mature structural stages and mature climax successional stages.