Effects of gypsy moth defoliation on forest birds: An assessment using Breeding Bird Census data

Although the gypsy moth (Lymantria dispar) is a significant insect pest of eastern deciduous forests in the United States, relatively little is known about its effects on forest bird communities. We used six Breeding Bird Cen sus sites from Connecticut, Pennsylvania, and Virginia to assess changes in bird species richness and individual species density in the years surround ing a gypsy moth outbreak. Individual species' responses were variable amon g states, and only a few species showed consistent responses to outbreaks a cross sites. Yellow-billed Cuckoos (Coccyzus americanus) and Black-billed C uckoos (C. erythropthalmus) appeared two years prior to an outbreak and the n disappeared immediately after an outbreak on four of the sites and increa sed in numbers on another site. Indigo Buntings (Passerina cyanea), which a re usually associated with open habitat, increased temporarily after outbre aks and then returned to pre-outbreak densities within 5 yrs after the outb reak. At the community or guild level, there was a significant reduction in species associated with closed-canopy forests during the outbreak year(s) compared with the average of all other years (before and after the outbreak ). There were no other general responses by the avian communities to the ou tbreaks, including associations with habitat preference, foraging guild, or nesting substrate. This study suggests that the effects of gypsy moth defo liation on the avian community are likely to be short-term (assuming that t ree mortality is not severe) and spatially variable. The minimal nature of these effects also suggests that compared with pesticide options for gypsy moth control, allowing the gypsy moth to defoliate, when feasible, is prefe rable when managing for forest birds.