Background/Question/Methods . Woodpeckers are considered ecosystem engineers because they excavate nest cavities that eventually provide habitat for other cavity nesting species. In aspen (Populus tremuloides) woodlands of the southern Rocky Mountains, red-naped sapsuckers (Sphyrapicus nuchalis) are the predominant woodpecker, providing essential nest cavities for multiple bird species. Sapsuckers also create sapwells in willows (Salix sp.), providing a sugary resource for many species. Previous work conducted near Gothic, Colorado indicated that sapsuckers avoid nesting in aspens far (> 500 m) from willows. Thus, the loss of willows could precipitate the local extinction of cavity-nesting species. However, previous work did not account for potentially confounding effects of other variables such as prevalence of the heart-rot fungus, Phellinus tremulae. The sapsuckers nest almost exclusively in Phellinus-infected aspens. Our objective was to use structural equation modeling to determine how willow proximity, Phellinus prevalence, and other variables influence nest-site choice by sapsuckers. These variables were measured in and around 0.25 ha circular plots of two types (n = 44 each): nest sites (centered on a sapsucker nest tree) and non-nest sites (centered on a suitable [>17 cm DBH] Phellinus-infected tree with no sapsucker nest in the tree or within a 100 m radius).
Results/Conclusions . Our preliminary results suggested that willow proximity was not an important factor in determining sapsucker nest-site location, especially after we accounted for the effects of other variables. The most important predictor variable appeared to be prevalence of Phellinus-infected aspens; nest sites had twice the Phellinus prevalence of non-nest sites. Our results indicated that sapsuckers chose nest sites primarily on the basis of tree suitability, not elevation, aspen grove density, or distance to willows, riparian areas or meadows. Thus, in order to conserve the aspen cavity-nesting community, we need to understand more about the ecology of the aspen heart-rot fungus.