Breeding performance and offspring quality can be affected by temporal and spatial variation in ecological conditions. We analyzed the concomitant effects of timing of breeding, ambient temperature at different stages of the breeding cycle, and microhabitat conditions (presence or absence of livestock farming) on breeding success, morphology, and immunity of the offspring in an aerially insectivorous passerine bird, the barn swallow (Hirundo rustica). A seasonal decline in breeding success was observed, while maximum offspring phenotypic values of different characters were attained at different times in the breeding season, depending on presence or absence of livestock farming. In addition, environmental temperature at different stages of the breeding cycle (pre-incubation, incubation, and nestling stage) of individual pairs affected all the components of nestling phenotypic quality. The results of this correlational study suggest that parents are faced with complex decisions about optimal timing of breeding and microhabitat choice. In addition, different ecological factors seem to interact in influencing breeding success and offspring quality in the barn swallow. Natural and anthropogenic changes in ecological conditions, including ambient temperature and distribution of livestock, may therefore affect distribution and productivity of a population of a declining passerine species.