DO POTENTIALLY VIRULENT MITES AFFECT HOUSE WREN (TROGLODYTES AEDON) REPRODUCTIVE SUCCESS?

Abstract

We tested the hypothesis that blood-feeding mites adversely affect House Wren (Troglodytes aedon) reproductive success. We measured the effects of natural mite numbers on nestling mass, nestling survival, and length of the nestling period during the summers of 1990 and 1992, and used path analysis to examine the effects of unmanipulated mite numbers on nestling health. We also investigated whether an experimental reduction in mite numbers affected nestling mass, length of the nestling period, and subsequent reproductive success of female House Wrens. Among unmanipulated nests, mite load had no discernible effect on the mass and survival of nestling House Wrens or on length of the nestling period. Similarly, broods with ex- perimentally reduced numbers of mites did not differ significantly from unmanipulated broods in nestling mass, survival, or length of the nestling period. We also detected no effect of experimentally reduced mite numbers on subsequent reproductive success of female House Wrens. Transmission rate and virulence in parasites are often positively correlated, and mite transmission rate at the study site is high. Virulence, however, is usually low. We propose that removal of old nests from nesting cavities by male House Wrens and unfavorable microclimatic conditions in the nest combine to reduce the initial size of mite populations. This usually slows the mite population growth sufficiently to permit nestlings to leave the nest before mites reach levels that produce detrimental effects.