Forest birds exhibit variable changes in occurrence during a mountain pine beetle epidemic

Abstract

Recent epidemics of mountain pine beetles (Dendroctonus ponderosae) have fundamentally altered forests of the Intermountain West, impacting management decisions related to fire, logging, and wildlife conservation. We evaluated how a recent mountain pine beetle epidemic influenced the site occupancy of 39 avian species in forests dominated by ponderosa pine (Pinus ponderosa) on the Helena National Forest, Montana. Point count data were collected during the avian breeding seasons (May–July) of 2003–2006 (pre-epidemic) and 2009–2011 (during-epidemic). We used a community-level Bayesian hierarchical model accounting for imperfect detection to obtain occupancy estimates for all detected forest birds. Our model for site occupancy included the annual presence of mountain pine beetles, the proportion of ponderosa pine at sites, the interaction between the two, and a random effect of year. We observed changes in occurrence over the study period for 23 of 39 species, including shifts toward and away from beetle-killed ponderosa pine. Community turnover increased during the epidemic and then returned quickly to pre-epidemic levels. Our results illustrate the myriad habitat preferences of the small landbird community and suggest that a mosaic of disturbed conifer, intact live conifer, and adjacent aspen forests will be critical for the persistence of populations of native avifauna in the Intermountain West.