Although it is generally assumed that effects of the developmental environment are transient and have little impact on adult phenotype, a growing number of studies have found persistent effects of developmental stress on adult morphology and physiology. Several studies have found long-term effects of early nutritional conditions on morphology, secondary sexual characters, and physiology. However, it is likely that other sources of developmental stress may also have long-term effects on offspring phenotype. In particular, exposure to parasites and other pathogens either during the breeding period of mothers or during early ontogeny may have profound effects on adult morphology. Ring-necked pheasants (Phasianus colchicus ) and European starlings (Sturnus vulgaris ) naturally suffer from high levels of intestinal parasitism (in our population over 90% of birds have at least one worm). These parasites include the nematodes Heterakis gallinarum , Syngamus trachea , and capillary worms (Capillaria spp.). We are experimentally manipulating levels of intestinal parasitism during the breeding period of mothers and during different periods of offspring development to assess the effects of parasitism on growth, immune function and the development of sexual ornaments, e.g., spurs, wattles and feathers. Developmental stress induced by intestinal parasitism may have long-term effects on morphology and ornamentation, thereby maintaining ornamentation as an honest signal of an individual's developmental history and possibly genetically based parasite resistance.