Avian community response to a mountain pine beetle epidemic
Mosher, Brittany Ann
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Recent epidemics of mountain pine beetles (Dendroctonus ponderosae) will fundamentally alter forests of the Intermountain West, impacting management decisions related to fire, logging, and wildlife conservation. We evaluated effects of a recent mountain pine beetle epidemic on site occupancy dynamics of 49 avian and one mammal 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 2003-06 (pre-epidemic) and again during 2009-10 (during epidemic). We used a Bayesian hierarchical model that accounts for detection probability to obtain occupancy estimates for rare species as well as common ones. We used one model to investigate changes occupancy for all species with respect to the timing of the beetle outbreak and then used a second model to determine whether the relationships seen were associated to changes in snag density. Results show that 30% of species exhibited strong short-term associations between occupancy probability and the occurrence of the beetle epidemic and 12% of species exhibited strong short-term associations between occupancy probability and snag density. Predictions were partially met, as we saw short-term increases in occupancy probability for beetle-foraging species, decreases for some foliage-gleaning canopy insectivores, and intermediate amounts of change for many ground and shrub insectivores. While short-term ecological changes caused by a mountain pine beetle outbreak were associated with changes in occupancy rates for individual species, the overall species richness of native avifauna was unaffected. Though further study over a longer period of time will be necessary to understand the complete dynamics of this disturbance, our results suggest that well-planned salvage operations after beetle outbreaks could also maintain suitable habitat for successfully breeding avian species.