Annual variation of immune condition in the Hooded Crow (Corvus corone cornix)

Little is known about indices of health condition in free-living populations and particularly about the presence of significant fluctuations of these indices between years. We assessed blood and immunological condition in wild Hooded Crows (Corvus corone cornix) in NW Italy for three years (1997-1999). Crows did not show any year-to-year difference in erythrocyte sedimentation rate, leukocyte abundance, and heterophyl/lymphocyte ratio. In contrast, we observed significant annual differences in albumin and immunoglobulin values. The albumin/immunoglobulin ratio was lower in 1998, a year when the size of two immunocompetence organs (bursa of Fabricius and spleen) was also smallest. Neither population density nor climate were likely to affect the observed variation of immune condition, annual censuses not revealing any noticeable density variation during the study period, and rainfall and mean temperatures being similar. The results show that in natural populations between-year variation of immune condition may exist, and that in our study, species immunoglobulin assays were more effective than leukocyte counts to detect them.