Modeling population dynamics of a songbird exposed to parasitism and predation and evaluating management options

Nest predation and parasitism are the primary causes of reproductive failur e in northern temperate passerine songbirds. I demonstrate the use of a two -step modeling approach to determine the implications of parasitism and nes t predation for the population dynamics of songbird populations and to quan titatively evaluate alternative options for their management I used a model to predict seasonal fecundity from parameters of nest success, productivit y, and breeding season length (Pease & Grzybowski 1995) and a stage-based m atrix model to examine population dynamics. I used this approach to model t he population dynamics of the Puerto Rican Vireo (Vireo latimeri), a single -island endemic species that Is exposed to high rates of parasitism by a no nnative brood parasite and to nest predation by introduced mammalian predat ors. The analysis showed that the introduction of the Shiny Cowbird (Moloth rus bonariensis), rather than the mammalian nest predators, caused this pop ulation to become a "sink" and is probably the cause of recent population d eclines. Moreover, the analysis explicitly shows that knowledge of the rela tionships among parasitism, predation, and population growth rate can aid i n designing an effective conservation strategy This modeling approach can b e used to determine the reproductive health of a population over a range of parasitism and predation values, to test alternative hypotheses for the ca use of an observed population decline and to make a priori predictions abou t the outcomes of specific management actions.