Black-Backed Woodpecker Nest Density in the Sierra Nevada, California

Chad T Hanson,Tonja Y Chi

doi:10.3390/d12100364

Abstract

In the western U.S., the black-backed woodpecker has been found to be associated with dense montane conifer forests with high snag densities, typically resulting from moderate- to high-severity wildland fires. However, black-backed woodpeckers are occasionally also detected nesting in unburned forests, raising questions about the type of habitat in which they nest and the potential abundance of such habitat. We conducted intensive black-backed woodpecker nest density surveys in large plots within the middle/upper-montane conifer forests of the Sierra Nevada, California, within general (undisturbed) forests, snag forest habitat from moderate/high-severity wildland fire, and unburned snag forest habitat from drought and native bark beetles. We found black-backed woodpeckers nesting only in the two snag forest conditions, mostly in burned snag forest, and their preferential selection of burned snag forest was statistically significant. No nest was found in general forests. Our spatial analysis indicates that snag forest is rare in the forests of the Sierra Nevada due to fire suppression and logging, raising concerns regarding small population size, which we estimate to be only 461 to 772 pairs in the Sierra Nevada.

Highlights

In the Sierra Nevada mountains of California, USA, the black-backed woodpecker (Picoides arcticus) is an uncommon species associated with dense middle/upper-montane conifer forests recently burned in mixed-severity wildland fires [1,2]
The extent to which black-backed woodpeckers nest in unburned snag forest habitat in the Sierra Nevada, as they do in the old boreal forests of eastern Canada [8,9,17], is relevant, given the extensive pulse of snag recruitment in unburned forests that occurred mainly in 2015 and 2016 in the southern and central Sierra Nevada during extreme drought conditions, killing >20–30% of the trees in numerous areas [23,24]. We investigated this issue by conducting black-backed woodpecker nest density surveys in the general forests, unburned snag forests, and burned snag forests of the Sierra Nevada, measuring the snag basal area at nest sites and estimating the current spatial extent of snag forest habitat in these forests
We found a total of 0, 2, and 5 active black-backed woodpecker nests in the general forest, unburned snag forest, and burned snag forest plots, respectively

Summary

Introduction

In the Sierra Nevada mountains of California, USA, the black-backed woodpecker (Picoides arcticus) is an uncommon species associated with dense middle/upper-montane conifer forests recently burned in mixed-severity wildland fires [1,2]. Black-backed woodpeckers have been detected in unburned forests with elevated levels of snags, including in the Sierra Nevada [5], eastern Oregon [6], and the Black Hills of South Dakota [7]. There is uncertainty about the type and spatial extent of the existing habitat for this species, and corresponding uncertainty about the current population level of black-backed woodpeckers in the Sierra Nevada. This uncertainty is compounded by ongoing forest management practices that encourage the logging of snags in unburned forests and target dense, older forests for logging activities and the removal of mature, live trees [10]

Methods

Results

Conclusion