RESPONSES OF ZEBRA FINCHES (TAENIOPYGIA-GUTTATA) TO EXPERIMENTAL INTRASPECIFIC BROOD PARASITISM

We experimentally examined the responses of captive Zebra Finches (Tae niopygia guitata) to intraspecific brood parasitism by adding two eggs to clutches at the onset (early treatment), in the middle (midtreatme nt), or at the end (late treatment) of egg laying. A comparison group was derived from nonparasitized nesting attempts of the same pairs. Ex perimentally parasitized nests were abandoned before hatching could ha ve occurred at a much higher rate than were unmanipulated nests; most of the abandonment occurred in early-treatment nests. Females in the e arly treatment also appeared to curtail egg laying. A smaller proporti on of eggs in experimentally parasitized nests survived, but survival of host and parasite hatchlings in such nests was equivalent. Within n ests containing both host and parasite young, host young were heavier at day 10 posthatching; the cause of mass differences was not ascertai ned. Egg loss occurred relatively more frequently in manipulated than in unmanipulated nests, suggesting that clutch enlargement taxes paren tal capabilities.