Abstract. Studies have found that cowbird offspring have increased fitness when sharing the nest with host young due to a greater feeding rate to the nest and disproportionate success by cowbirds at receiving feeds.  One would expect that a parasitism strategy favoring the survival and vigor of some host young would have a positive effect on cowbird fitness.  Since asynchronous hatching can affect cowbird fledging success and host hatching/fledging success, one mechanism that could ensure the survival of host and cowbird young would be optimal timing of egg-laying by cowbirds such that both cowbird and host eggs hatch at the same time.  Therefore, cowbird habitat features that facilitate optimal timing of egg-laying could maximize hatching synchrony and ultimately cowbird fitness.  I addressed these phenomena by asking: 1) is habitat a good predictor of cowbird hatch synchrony and 2) does habitat indirectly influence cowbird fitness?  I am testing the hypothesis that synchronous nests will be less concealed, closer to perches, and located in areas of higher host density than asynchronous nests.  Additionally, I tested the hypothesis that nestlings in synchronous nests will develop faster than those in asynchronous nests.  Neither hypothesis was supported in either song sparrow (Melospiza melodia) or yellow warbler (Dendroica petechia) nests.  Habitat was not a good predictor of hatch synchrony and variation in growth rate was mostly explained by sex and not by hatch synchrony.  Lastly, post hoc analysis revealed that synchrony was sex dependent.