Additional observations of age‐dependent migration behaviour in western honey buzzards Pernis apivorus

Abstract

The western honey buzzard Pernis apivorus is a summerresident in Europe that winters in west-central Equator-ial Africa (Cramp and Simmons 1980). Individuals ofdifferent ages migrate in different periods. Adults moveabout two to three weeks earlier than juveniles (Kjelle´n1992, Agostini and Logozzo 1995). In a recent paper,Hake et al. (2003) reported data on the autumnmigration of nine honey buzzards (six adults and threejuveniles) from Sweden that were tracked by satellite.The results showed that whereas adults crossed theMediterranean Sea at the Straits of Gibraltar, juvenilesmigrated on a broader front and undertook longpowered flights ‘‘somewhere’’ over the open sea. Visualobservations in the central Mediterranean region clearlyshowed the existence of different spatial migrationpatterns between adult and juvenile honey buzzardsduring post-reproductive movements (Agostini andLogozzo 1997, Agostini et al. 1999, 2000, 2002).Unfortunately, Hake et al. did not quote these sourcescausing a gap in their work. Here I review these papers inan effort to fill this gap.In the central Mediterranean, adult honey buzzardsmigrate mainly from late August through early Septem-ber (Agostini and Logozzo 1995). Here they tend tofollow the Italian peninsula and, upon reaching theStraits of Messina between the ‘‘toe’’ of southern Italyand Sicily turn west. Many of them will fly across Sicily,and then southwest across the Sicilian Channel headingtowards the Cap Bon peninsula (Agostini and Logozzo1997, Agostini et al. 2000, Fig. 1). The experienced adultbirds probably use the reverse of the spring route(Agostini et al. 1994, Agostini and Logozzo 1998).Thus Agostini and colleagues concluded that adulthoney buzzards apply true navigational abilities, thusavoiding a longer flight across the central Mediterra-nean, probably to minimize risks and energetic costs(Agostini and Logozzo 1997, Agostini et al. 2000). Onlya few juveniles migrate together with adults on thismigration route (Agostini et al. 1999, 2000). Most ofthem arrive at least two weeks later at the coasts of theMediterranean, typically in all juvenile flocks or alone.Unlike adults, juveniles passing through southern con-tinental Italy after the second weekof September take offin southern Sicily and then concentrate over Malta toreach probably Libya, moving along a NE-SW innateaxis (Fig. 1, Agostini and Logozzo 1995, Agostini et al.1999). During their first migration, inexperienced juve-nile honey buzzards are not familiar with the shortestroute to cross the central Mediterranean and presumablyare moving along innate migratory directions. It isinteresting to note that observations at the Circeopromontory (central Italy, Fig. 1) and over Maltasuggest that at least part of the juveniles crossing theTyrrhenian Sea change their innate direction of migra-tion in response to the open water (Agostini et al. 2002,see also Agostini et al. 2004). In the case of juvenilehoney buzzards Agostini and colleagues (2000, 2002)concluded that these spatial migration patterns mayexplain why they show a broader front in migration, andwhy concentrations of juveniles but only a few adults arereported at many islands of the Mediterranean, such asCabrera, Corsica, Capri, Pianosa, Malta andCyprus (Frost 1994, Rebassa 1995, Agostini et al.