Temporary shift of body size in hooded crows Corvus corone cornix of NW Italy

Unusual climatic events are known to influence micro-evolutionary changes in birds through selection and directional evolution of body size. In NW Italy a notable climatic episode occurred from 1984-85 to 1986-87 when the winters were unusually severe. In the periods 1986-88 and 1997-2000 we measured the body size and mass of 808 adult hooded crows. Body size measurements of specimens collected from the same area but in two other periods (1950 and 1974) were also considered for comparison. In the 1986-88 sample (just after the unusual climatic period), there was a significant shift of body size, with a greater tarsus length than in the other three periods; body mass was also higher than in 1997-2000. The peak in tarsus length and body mass is discussed with regard to the severe weather in the winter which could have acted as a strong directional selective factor, favouring bigger birds, or may have prompted irruptive movements of Northern larger crows.