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60                               SHORT COMMUNICATIONS                   VOL. 41, NO.1

      autumn migration (Agostini et al. 2005b). In particular,  winds, the difference in energetic costs of powered flight
      those passing via Pantelleria used a curvilinear flyway, ap-  over water vs. soaring flight over land is likely lower than
      parently choosing the shortest route between North Africa  the difference during head winds. Finally, the location of
      and this central Mediterranean island, where they changed  breeding areas might also play a role in the decision of
      their orientation and flew NE toward western Sicily. They  whether or not to cross the Tyrrhenian Sea; in particular,
      probably applied true navigational abilities, as Pantelleria  birds breeding in southernmost Europe may be less reluc-
      is nearly always out of sight from Tunisia (Agostini pers.  tant to make the sea crossing because they are nearing the
      obs.). Flocks using this flyway with W-WNW-NW winds flew  end of their migration and flying in large numbers over
      in tailwinds between the Cap Bon Peninsula and Pantel-  wide water surfaces (Agostini and Panuccio 2005). Obser-
      leria, and then moved in lateral winds from Pantelleria to  vations of thousands of European Honey-buzzards seen
      western Sicily. In contrast, during N-NNE winds, birds per-  undertaking further sea crossings between the Italian Pen-
      haps allowed themselves to drift ESE toward Pantelleria,  insula and the former republic of Yugoslavia and Albania
      thus avoiding flying directly into the wind, and later flew  are consistent with this hypothesis (Gustin and Sorace
      about 110 km in head winds between that island and west-  2004, Premuda et al. 2004). In conclusion, our study sug-
      ern Sicily. As a result, during both W-WNW-NW and N-  gests that prevailing winds, geography, navigational abili-
      NNE winds, birds saved energy during the first stage of  ties, and the time of the day interact to shape the migra-
      the crossing; upon reaching Pantelleria, they interrupted  tory paths of European Honey-buzzards.
      their non-stop powered flight over water, exploiting ther-
      mals over land before undertaking the final sea crossing
                                                 FACTORES QUE DETERMINAN LAS RUTAS DE PERNIS
      from Pantelleria to western Sicily at a higher altitude. As
                                                 APIVORUS DURANTE LA MIGRACIO ´ N DE PRIMAVERA
      during their autumn migration, this flight pattern of inter-
                                                 EN LA DEPRESIO ´ N CENTRAL DEL MEDITERRA ´ NEO
      rupting the powered flight over water could lower the risk
      of unpredictable weather changes during the water cross-  RESUMEN.—Observamos a individuos de la especie Pernis
      ing, and may perhaps result from a conservative strategy  apivorus en puntos migratorios cerca del Mar Mediterra´-
      (Agostini et al. 2005b). Moreover, passing mostly in the  neo central. Se realizaron observaciones simulta´neas entre
      afternoon, the birds at Pantelleria were probably more  el 25 de abril y el 20 de mayo de 2004 en las islas Maret-
      fatigued than those undertaking the sea crossing in the  timo, Pantelleria (localizadas a los costados norte y sur del
      morning and thus more reluctant to fly directly toward  canal de Sicilia, respectivamente), Panarea y en los estre-
      western Sicily from the Cap Bon Peninsula. Conversely,  chos de Messina (ambos al el este de Sicilia). La bandada
      during WSW-SW-SSW winds flocks passed mostly over Mar-  se utilizo´ como unidad de muestreo. Un total de 216 ban-
      ettimo, probably exploiting the tailwind to minimize ener-  dadas pasaron vı´a Pantelleria, la mayor parte durante vien-
      getic costs. However, during south-westerly winds, a lower
                                                 tos N-NNE y W-WNW-NW con un pico evidente a finales de
      proportion of flocks was seen at Marettimo–Pantelleria
                                                 la tarde y durante el atardecer. Las aves escogieron cruzar
      compared to that observed in eastern Sicily (Panarea–
                                                 por la ruta ma´s corta entre el norte de A ´ frica y Pantelleria
      Straits of Messina). Probably, during such winds, many  utilizando una migracio´n curvilı´nea sobre el agua. Durante
      flocks used a more direct path between North Africa and  los perı´odos de viento con direccio´n sur-oeste, P. apivorus
      western Sicily, bypassing both Marettimo and Pantelleria.  se registro´ principalmente en Marettimo a lo largo de la
      During observations made at the Ustica Island (Fig. 1),  ruta ma´s directa hacia el oeste de Sicilia; estas aves proba-
      European Honey-buzzards were seen flying quickly with
                                                 blemente aprovecharon los vientos de cola. Con vientos
      tailwinds, sometimes at a very low altitude over the water,
                                                 con direccio´n sur-oeste y durante las horas de la man˜ana,
      which was in agreement with our observations made at
                                                 P. apivorus mostro´ un frente de migracio´n ma´s amplio
      Panarea (Agostini et al. 2005a).
                                                 entre el este de Sicilia y la Penı´nsula Ita´lica (Estrechos
        Between eastern Sicily and Italian Peninsula (Straits of
                                                 de Messina–Panarea). Nuestro estudio sugiere que los
      Messina-Panarea) European Honey-buzzards migrated on  vientos predominantes, la geografı´a, las habilidades de na-
      a broader front in the morning and during south-westerly
                                                 vegacio´n y la hora del dı´a determinan las rutas migratorias
      winds, when a higher proportion of flocks crossed the
                                                 en esta especie.
      southern Tyrrhenian Sea via the Lipari Islands. Conversely,  [Traduccio´n del equipo editorial]
      flocks concentrated their passage via the Straits of Messina
      with N-NNE winds and during midday. These results might
      be explained by the fact that the thermals presumably are
      weaker in the morning than during midday, and, conse-  ACKNOWLEDGMENTS
      quently, the difference between energetic costs of flight
                                                   We thank Andrea Corso, Giuseppe Campo, Giovanni
      over land and over water is less consistent during the
                                                 Cumbo, Elisabetta Cutini, Guido Premuda, Giuseppe
      morning. Moreover, as we found for the Pantelleria–Mar-
                                                 Rossi, and Antonino Provenza for the field assistance. Fi-
      ettimo area, during south-westerly winds a higher propor-  nally, we thank F. Ziesemer and K. Huang for their useful
      tion of flocks might choose the more direct route to reach  comments on earlier drafts of the manuscript. The work
      the Italian Peninsula, exploiting the tailwinds. During tail-  was supported by grants of LIPU-UK.
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