Movement ecology of long-distance migrantsinsights from the Eleonora's falcon and other raptors

Resumen

The thesis focused on the study of raptors movements by means of satellite telemetry and is based mainly on the Eleonora's falcon, with several individuals being tagged with Argos tranbsmitters in the Western Mediterranean and in Morocco. The movement ecology of Eleonora's falcons is affected by both external (landscape, wind) and internal (age) factors. During their autumn migration across Africa, Eleonora's falcons change their behaviour according to the landscape characteristics of the crossed regions. Changes in flight speed, time budget and straightness promote differences in the daily flight ranges, also among adult and juveniles. Wind conditions affect the daily forward and/or perpendicular components of movement s rates. During the crossing of ecological barriers, such as the Sahara desert, they reach higher daily flight ranges thanks to a higher number of traveling hours, including a consistent amount of nocturnal flights. They are also more dependent of wind conditions than in other regions, regardless the age, with both tailwind and crosswinds shaping the migratory routes. In the remaining African regions the rate of nocturnal migration is lower than in the desert, as well as flight speeds, thus promoting lower daily distances. In particular, in the Sahel, a more benign region in terms of food availability, juveniles show slower speed, lesser straight paths and a higher amount of stop-over days than adults, perhaps in order to take advantage of foraging opportunities, in response to a lower efficiency during pre-migratory fattening. Wind conditions seem to be less important during the crossing of these regions, although crosswinds have a significant effect in Equatorial Africa. The likely reason of this pattern is that perhaps Eleonora s falcons fly and stop in relation to foraging opportunities rather than in relation to wind, especially in the Sahel and therefore, at least at the daily scale, wind conditions seem to be less important. In order to reach Madagascar, Eleonora's falcons have to fly non-stop over the sea for at least 600 km ca. While during autumn migration they try to minimize this distance, probably because winds are generally less favourable, during spring they reach Africa more directly, flying over water for 1200-1500 km and showing a strong flexibility, since the same individual is able to change the route in a given year in order to avoid low pressure areas where bad weather conditions can enhance mortality risks. The main seasonal difference in the geometry of migration routes is promoted by the significant divergence around the Equator, where routes lie more in the west during autumn and in the east during spring. This is probably dictated by seasonal differences in the distribution of trophic resources. Favourable conditions for foraging occur in Ethiopia during April, as suggested by the higher number of stop-over days in those regions. This pattern shapes a loop migration system that seems to be the rule among all the studied population of the Eleonora¿s falcon (Spain, Sardinia, Croatia, Greece), and may be widespread also among other long-distance Palearctic migrants. Taken together, these evidences (nocturnal migration, individual flexibility, long sea-crossings) suggest the Eleonora's falcon has an orientation system that may work independently of the visibility of landmarks or, at least, not relying only on these topographic features. Still, it remains unknown which cues it uses to reach a narrow wintering area as Madagascar, especially when considering inexperienced juveniles migrating alone. The Eleonora's falcon is a bird with long and narrow wings, that consequently moves mainly by flapping flight, irrespectively of thermal conditions and flying consistently also during night. Instead, soaring migrants can fly only during daytime, showing therefore lower daily flight ranges, usually around 200-250 km. The circadian pattern of hourly speed and flight altitude in four species of soaring raptors crossing the desert highlights the importance of thermal strength, with a clear peak just after midday. Instead, at the daily scale, their performance is affected mainly by tailwind support. Migration speed is higher for species that have to cover an overall longer distance (> 5000 km: Osprey and Marsh harrier) rather than for species with a shorter distance between breeding and wintering grounds (Egyptian vulture and Short-toed eagle). Finally, in agreement with predictions, adult individuals migrate more quickly during spring rather than during autumn. Outside the migration periods, when they perform long-distance directional flights, Eleonora's falcons move within small ranges, with shorter flights and in a non-directional way, using different habitat according to the distribution of trophic resources and showing among-year site fidelity to both wintering and pre-breeding areas. Wintering is the most consistent part of the annual cycle, accounting for a 41%. All tracked Eleonora's falcons, apart a juvenile wintering between Kenya and Tanzania, spent the winter in Madagascar, mainly on the eastern slopes of the northern part of the island. They select degraded humid forests and cultivations close to pristine humid forests, probably to take advantage of a spill-over effect of their preys (insects) into open areas where hunting is easier than in the dense forest. During late spring and summer Eleonora's falcon show a pre-breeding phase where they alternate stays in the breeding colony with long visits to inland areas that can be even 400 km distant and are characterized by a variety of environments offering, in this period, better foraging opportunities (e.g., insects' concentrations) than the breeding colonies. Instead, during the breeding season, Eleonora's falcon mostly moves to the open sea to hunt migrating passerines during morning, visiting inland areas with freshwater availability during afternoon and staying in the colony during night. Eleonora's falcons cross the boundaries of tens of countries, as well as a huge variety of habitats, facing many different threats. The loss of pristine humid forests in Madagascar and the pollution of areas used during the pre-breeding and the breeding season suggest that the species deserves a special attention from the conservation point of view, especially during winter, when the global population is concentrated in a very restricted range. Also other studies concerning different populations confirmed the importance of the areas and habitat that we have identified and may convert them into priority targets to focus protection efforts and field researches. The conservation of migratory species cannot be focused just on one area/season/life stage of a given species but should integrate local actions, spanning throughout the whole annual cycle, into a global strategy.