Local Weather Conditions Affect Migration Strategies of Adult Western Honey Buzzards Pernis apivorus through an Isthmus Area Michele Panuccio 1,2 , Nicolantonio Agostini 1,2, *, Giuseppe Lucia 1 , Ugo Mellone 1,3 , Stephen Wilson 1 , Jack Ashton-Booth 1 , Gianpasquale Chiatante 1 , and Simone Todisco 1 1 Mediterranean Raptor Migration Network (MEDRAPTORS), Via Mario Fioretti, Rome 18- 00152, Italy 2 Dipartimento di Biologia Animale, Univ. of Pavia, Via Ferrata 1, Pavia 27100, Italy 3 Current address: Grupo de Zoologia de Vertebrados/CIBIO, Univ. de Alicante, Apdo. correos 99, Alicante E-03080, Spain (Accepted May 5, 2010) Michele Panuccio, Nicolantonio Agostini, Giuseppe Lucia, Ugo Mellone, Stephen Wilson, Jack Ashton-Booth, Gianpasquale Chiatante, and Simone Todisco (2010) Local weather conditions affect migration strategies of adult Western Honey Buzzards Pernis apivorus through an isthmus area. Zoological Studies 49(5): 651-656. We tested the effect of crosswinds, barometric pressure, and time of day on the visible migration of adult Western Honey Buzzards Pernis apivorus through an isthmus area in southern continental Italy. Simultaneous observations from 3 posts were made in autumn 2005 and 2006, and birds were assigned to one of 3 local migration corridors: western, central, and eastern. During our observations, prevailing winds were perpendicular to the direction of migration. The peak of migration occurred during the afternoon and with westerly winds. Ideal weather conditions for soaring flight occurred during weak winds and high barometric pressure. An analysis of migration frequencies among the 3 corridors suggests that adult Western Honey Buzzards tend to compensate for deviations in lateral winds on a small scale when migrating through this isthmus area. It appears that they do not slow their travel speed during weather conditions that are unfavorable for soaring flight (strong lateral winds and low barometric pressure) by increasing the use of powered flight. On the other hand, migrants will change their migration strategy in relation to wind drift when migrating through the Channel of Sicily en route to Africa, thus showing a broad front of migration over water. http://zoolstud.sinica.edu.tw/Journals/49.5/651.pdf Key words: Western Honey Buzzard, Raptor migration, Wind drift, Central Mediterranean. *To whom correspondence and reprint requests should be addressed. E-mail:nicolantonioa@tiscalinet.it D uring migration, birds face a variety of challenges including geographical complexity, competition during stopovers, and the variability and unpredictability of meteorological conditions (Berthold 2001). In particular, weather conditions can affect flight behaviors and migration pathways on both large and small scales and ultimately a bird’s decision when to depart (Alerstam 1979, Richardson 1990, Maransky et al. 1997, Danhardt and Lindstrom 2001, Shamoun-Baranes et al. 2006, Agostini et al. 2005, Liechti 2006). In particular, sea-level pressure was shown to be one of the most important factors triggering the onset of soaring-bird migration (Shamoun-Baranes et al. 2003), and favorable winds can minimize both the time and energy birds allocate to migration (Houston 1998). General wind conditions can shape the migratory routes of raptors; for example, Klaassen et al. (2010) demonstrated how crosswinds cause Western Marsh Harriers Circus aeruginosus to partially drift thus promoting a loop migration. The Western Honey Buzzard Pernis apivorus is one of the most common raptor species recorded at migration hotspots in the Zoological Studies 49(5): 651-656 (2010) 651