Survey of Songbirds during a Spruce Beetle (Dendroctonus rufipennis) Outbreak on the Kenai Peninsula, Alaska

Abstract

A spruce beetle (Dendroctonus rufipennis) epidemic in southcentral Alaska has caused extensive mortality to spruce trees and a change in forest stand structure. Because a change in forest vegetation can influence composition and abundance of forest birds, we at- tempted to assess the type and magnitude of change in bird populations within 2 forest stands on the Kenai Peninsula that were undergoing differing levels of spruce beetle infestation. In addition, we compared bird populations occupying a salvage-logged forest site with those in the other forest stands. During our survey period (1994 to 1998), species composition and abun- dance of land birds differed across the sampled forest stands. Avian species diversity and rich- ness was greatest in the early successional stage of the logged forest and least in the heavily infested forest stand where many spruce trees killed by the spruce beetle had fallen to the ground. As predicted, ground nesting and foraging bird species increased where trees had fall- en or were removed. Conversely, the abundance of mature conifer forest birds, such as Town- send's warblers (Dendroica townsendi) and ruby-crowned kinglets (Regulus calendula) decreased in those forest stands that lost overstory structure. Townsend's warblers declined in abundance through time, potentially due to the loss of mature conifers for nest sites. Bird abundance was greater within the lightly infested stand in 1996, possibly due to immigration of birds from less suitable habitats. Because forest stand characteristics will continue to change through time fol- lowing the spruce beetle epidemic, we suggest that songbird communities will also remain dy- namic in response to changing habitats.