Tree swallow reproductive investment, stress, andparasites

We reduced or increased tree swallow, Tachycineta bicolor (Vieillot, 1808), clutch sizes by three eggs (50% of modal clutch size) to test experimentally for relationships between stress and parasite loads. In the first year of the study (1996), we enumerated two measures of stress (granulocyte to non-granulocyte ratios and heterophil to lymphocyteratios), blood parasites, and ectoparasites living on birds (and not in nesting material). Stress indices increased for parents, but not for nestlings, associated with larger broods. Only one blood parasite (a trypanosome) was detected in blood smears from 221 different individuals.

Dave Shutler, Adele Mullie, and Robert G. Clark, Can. J. Zool. 82: 442-448 (2004)