Eastern towhee numbers increase following defoliation by gypsy moths

Abstract

Bird populations and habitat were monitored each year before (1984 to 1986), during (1987 to 1988), and after (1989 to 1996) a major gypsy moth (Lymantria dispar) outbreak in the eastern panhandle of West Virginia. Extensive tree mortality caused by repeated defoliations by gypsy moths resulted in the release of understory vegetation. Densities of Eastern Towhees (Pipilo erythrophthalmus) were significantly higher in the period following the gypsy moth outbreak. Both before and after the outbreak, Eastern Towhee densities were higher in areas of the forest with less overstory (particularly high canopy) and lower densities of live trees (particularly small trees). This indicates that not all forms of early successional habitat, specifically areas with a high density of small-diameter trees, are suitable for species deemed as 'early successional.' Although the gypsy moth outbreak resulted in an increase in the number of saplings, it also opened up the canopy and created a dense layer of shrubs in many areas. Because Eastern Towhees forage and nest on the ground and in shrubs, the outbreak increased the amount of suitable habitat for this species. Given that densities of Eastern Towhee are declining in the state, it is useful to document habitat features that are important for sustaining towhee populations.