American Three-Toed Woodpecker Response to Burn Severity and Prey Availability at Multiple Spatial Scales

Abstract

We evaluated American three-toed woodpecker (Picoides dorsalis) response to spatial heterogeneity of burn severity and prey availability over multiple scales at the 56 000 ha Hayman Fire (2002) located in the Colorado Front Range. In 2003 and 2004, we quantified the response of three-toed woodpeckers to burn severity, beetle occurrence, and tree size at three levels: home-range scale (36 ha), foraging patches (∼1 ha), and trees within foraging patches. We used the differenced normalized burn ratio (dNBR) to quantify burn severity at the home range scale. Woodpecker response to burn severity was strongly scale dependent. Three-toed woodpeckers generally established territories in moderately burned areas containing patches of live and dead trees, and were less common in unburned forests and in large severely burned areas lacking live trees. Woodpeckers disproportionately foraged in patches with a higher proportion of severely burned trees than were available in moderately burned areas, but rarely foraged in severely burned patches within severely burned areas. Burn severity was similar among trees within foraging patches and was not useful for predicting woodpecker use at this scale. Three-toed woodpecker response to beetle occurrence and tree size also varied across scales. Tree size and beetle occurrence were both greater in foraging patches compared to available trees. At the largest scale (home range), burn severity best accounted for three-toed woodpecker use, whereas tree size and beetle occurrence played a stronger role at the smallest scale (individual trees). At the intermediate scale (foraging patches), all factors were important in explaining woodpecker use. Our results indicate that the scaling of burn severity patterns can affect the woodpecker’s use of burned forests and demonstrate the importance of evaluating burn severity across multiple spatial scales. The prevalence of breeding three-toed woodpeckers in mixed-severity areas with both lightly and severely burned trees highlights the importance of mixed-severity regimes to such fire-dependent species and the need for fire management that includes a range of fire behaviors, including high-severity fires.