The effects of body state on nest sanitation and provisioning effort in breeding barn swallows (Hirundo rustica)

Parent birds feeding young are faced with a trade-off between allocating time and allocating energy to many variables, all of which will influence fitness to some degree. Here I use a novel experimental approach to determine the importance of nest sanitation and nest provisioning as components of reproductive effort in female barn swallows (Hirundo rustica L., 1758) feeding nestlings aged 11-15 days. Female birds were warmed overnight to allow extra energy at dawn and the short-term consequences for reproductive behaviour were determined upon release. Faecal sac removal rates were significantly positively related to nest visitation rates and warmed females showed a nonsignificant trend towards elevated sanitation behaviour. Females also showed a highly significant increase in nest visitation rates in response to the warming treatment compared with the controls. Precipitation had a significant negative effect on provisioning behaviour across all treatments. Nestling swallows were observed ejecting faecal sacs from the nest without parental help, and this precipitated a very low rate of faecal sac removal. The results suggest that nest sanitation may be an opportunistic behaviour in swallows and that it may not be an important component of reproductive effort in birds with older nestlings. The results also suggest a trade-off between nest sanitation and nest provisioning.