Bird Populations and Habitat in Bacillus thuringiensis and Dimilin-treated and Untreated Areas of Hardwood Forest

Abstract

-The objective of this study was to evaluate the effects of a gypsy moth (Lymantria dispar) infestation on nongame bird populations and habitat. This study was conducted at the Sleepy Creek Public Hunting and Fishing Area in Morgan and Berkeley counties, and Cacapon State Park in Morgan County, in the eastern panhandle of West Virginia. We compared an area that was repeatedly defoliated by the gypsy moth (Sleepy Creek) to an area (Cacapon) that was sprayed with Dimilin and Bt to control gypsy moth populations. Both areas were sampled in 1984, before defoliation or spraying, and afterwards in 1993. Tree mortality caused by gypsy moth defoliation created gaps in the canopy, increasing habitat patchiness at Sleepy Creek, but did not negatively affect total bird density. Greater habitat complexity (particularly increases in snags, windfall and shrub cover) after the gypsy moth outbreak may have increased available nesting and foraging resources for many bird species. While habitat for some flycatchers and canopy-dwelling species was reduced at Sleepy Creek, sufficient canopy was left after defoliation to support similar numbers of these birds. Despite dramatic visual effects, gypsy moth impact may not be permanently damaging to bird populations and may even be beneficial for some species. However, other factors, such as insect availability, nesting success, predation and cowbird parasitism need to be examined in gypsy moth-impacted areas to better assess effects of defoliation on bird populations.