Immunocompetence and Parasitism in Nestlings from Wild Populations

Summary: Nestling is a defenceless stage in the life of birds in several ways. For instance, the possibilities to escape infection and infestation by several parasitic diseases are greatly reduced in nestlings. This fact implies that a number of strategies and counter strategies could evolve in hosts to avoid parasites and in parasites to locate and exploit young hosts. An increasing number of nestlings in a nest may support more parasites and thus increase competition between siblings to avoid parasitism. In addition, parental effort may vary in the presence of parasites resulting in different effects of parasitism on nestlings. Moreover, nestling investment in immunity may increase in the presence of parasites at least up to a limit marked by the ability of parents to get resources for their nestlings. In this respect, the transfer of immunoglobulins and other resources from the female parent to eggs may be of considerable importance during the first days of nestlings´ life. However, increased parental activity may also attract more parasites to the nest. A recent work using a metaanalytical approach suggests that parasite-induced nestling mortality in birds is mainly determined by geographical location and to a smaller extent nest site and parasite prevalence. The naive immune system of nestlings and the difficulties to avoid infection once the nest has been located, imply a high potential impact of parasites on nestlings. Thus parasites could cause an important reduction of host population productivity through their effects on nestlings.