COS 39-6
Does brood parasitism affect host nestling diet?
The goal of this study was to test predictions of the effect of avian brood parasitism on host nestling diet and nutrition. Food and nutrient limitation can have negative effects on survival, fecundity, and lifetime fitness of individuals, which can ultimately limit populations. Changes in trophic dynamics and diet patterns, affected by brood parasitism have not been studied, yet may play an important role in population regulation. We estimated diets of wood thrushes (Hylocichla mustelina), a Neotropical migratory songbird species, and tested predictions of how brood parasitism by brown-headed cowbirds (Molothrus ater) may affect wood thrush nestling diet and daily calcium (Ca) intake. We measured carbon (δ13C) and nitrogen (δ15N) stable isotopes of seven invertebrate food sources (snails, spiders, isopods, earthworms, myriapods, insects, and caterpillars) and in blood plasma from adult male and female wood thrushes, and from wood thrush nestlings in nests with and without cowbird nestlings.
Results/Conclusions
Wood thrush diet compositions were largely comprised of Ca-rich foods (36-73%, 95% highest density intervals (HDI)), including snails, isopods, and myriapods, as well as spiders (25-35%, 95% HDI). Caterpillars were the least common food item in wood thrush diets (0.03-3 %, 95% HDI). Wood thrush nestling diet in nests without cowbirds contained greater proportions of Ca-rich foods and spiders compared to the diet of nestlings in parasitized nests. These findings suggest that wood thrushes showed an obvious preference for Ca- and protein-rich foods, which may have important implications for adult survival and fecundity, as well as nestling nutrition and development. Our results demonstrate for the first time, that brood parasitism can potentially affect developing nestlings through nutritional stress that may, in turn, affect survival, fecundity, and ultimately limit population growth.