NEST WEIGHT AND FEMALE HEALTH IN THE BLUE TIT (CYANISTES CAERULEUS)

Abstract

Abstract We explored two hypotheses that may explain intraspecific variability in nest size. The “thermoregulatory” hypothesis states that species adjust nest size to maintain egg temperature and minimize temperature fluctuations in the nest. Recently, the suggestion has been made that nest size may reflect the health status or phenotypic quality of the builder, potentially making it a sexually selected trait (“sexual selection” hypothesis). For two years, we weighed nests of Blue Tit (Cyanistes caeruleus) at initiation of reproduction in a nest-box breeding population in central Spain. We recorded laying date, clutch size, incubation period, and hatching success. We measured and took blood samples of adult females when nestlings reached three days of age. General regression models controlling for potential variables that could affect nest weight revealed that prevalence of Trypanosoma avium and immunoglobulin levels in females were significantly related to nest weight in only one of the study years. Fema...