Effects of Gypsy Moth Infestation on Black Bear Reproduction and Survival

Abstract

During 1985-90 in Shenandoah National Park, Virginia (SNP) a gypsy moth (Lymantria dispar) infestation resulted in widespread overstory canopy defoliation and a complete acorn crop failure in defoliated areas. We believed these habitat and food supply alterations would adversely affect SNP black bear (Ursus americanus) reproduction and survival. We compared aspects of bear population dynamics between years of extensive gypsy moth defoliation and years immediately before the infestation (1982-84). Despite acorn failure, infestation had no detectable effect on bear reproduction or survival. Litter sizes before (x = 2.0) and during (x = 2.3) years of extensive defoliation did not differ (P = 0.191). Radiomarked females produced cubs by age 4 (28% of 3 yr olds produced cubs), in alternate years, and none skipped an opportunity to reproduce. Five known primiparous mothers gave birth to at least 11 cubs and reared 10 of them to 1 year of age. Survival of all age/sex cohorts did not differ (P > 0.10) from predefoliation levels. The results of this study demonstrate that variability in annual acorn crops do not solely explain fluctuations in bear reproduction and survival, and indicate the importance of alternate fall food sources (i.e., soft mast) to bears.