In this study we analyse the age and sex ratios of marsh harriers wintering in central Italy and Sicily. Among adults, most individuals were females (88%), whereas males accounted for only 12% of the observations. There was no difference in the proportion of juveniles and adults. The remarkable difference in numbers of males and females seems to support the hypothesis that, at least among adults crossing the central Mediterranean, males show a stronger tendency to migrate over longer distances. Among the proposed hypotheses explaining intraspecific differences in avian migration patterns, the Bergmann’s rule, which predicts that larger individuals (i.e. females in this case) are better adapted to survive in colder climates, appears to be in agreement with our results, whereas other hypotheses based on social dominance are less supported by our data, as suggested by the similar proportion of juveniles and adults.
Observations on the autumn migration of honey buzzards Pernis apivorus, black kites Milvus migrans, marsh Circus aeruginosus and Montagu’s harriers Circus pygargus were made between 24 August and 10 September 2004 at the western slope of the Calabrian Apennines (Straits of Messina) and over Panarea (Lipari Islands). The aim was to compare the post-reproductive migration patterns of these raptors over land and over water along two parallel flight paths, as well as to verify the existence of a migratory movement of the black kite across the southern Tyrrhenian Sea in this period. Atotal of 7738 raptors were counted at both sites, most of which were honey buzzards (73.7%), black kites (9.1%) and marsh harriers (16.0%). Only 838 birds were seen over Panarea, most of which were marsh harriers (75.3%). No black kites were observed on Panarea. Thus, while marsh harriers migrated on a broad front, honey buzzards and black kites migrated over land and approached the Straits of Messina en route towards the Channel of Sicily, between western Sicily and Cap Bon in north Africa. This study shows no indication of a black kite migration across the southern Tyrrhenian Sea. Finally, our results confirm that, unlike spring migration, few Montagu’s harriers cross the Central Mediterranean during post-reproductive movements.
