Short-term effects on body condition and size of immunocompetent organs in the hooded crow

Only recently have there been attempts to assess the short-term variations of indices of body conditions and immunocompetence in free-living populations, and to evaluate the presence of significant fluctuations of these indices between years. We compared body conditions and size of immunocompetent organs (spleen and bursa of Fabricius) in wild populations of hooded crows in NW Italy during three years. Differences in population density among sites did not influence any of the variables, while a great difference was found between adult and subadult birds. In the study period, adults did not show any year-related variation of mass, structural size, lean mass (as assessed by TOBEC electro-conductivity index), and spleen mass. Instead subadults of both sexes showed differences among years in mass; subadult females had the lowest values of bursa and spleen mass in the year when mass was smallest. The results show that in natural populations between-year variation of body conditions may exist. Subadults are probably most sensitive to adversities producing short-term variations in body conditions.