Interspecific comparison of the performance of soaring migrants in relation to morphology, meteorological conditions and migration strategies

This is an open-access article distributed under the terms of the Creative Commons Attribution License.-- et al.[Background]: Performance of migrating birds can be affected by a number of intrinsic and extrinsic factors like morphology, meteorological conditions and migration strategies. We compared travel speeds of four raptor species during their crossing of the Sahara desert. Focusing the analyses on this region allows us to compare different species under equivalent conditions in order to disentangle which factors affect migratory performance. [Methodology/Principal Finding]: We tracked raptors using GPS satellite transmitters from Sweden, Spain and Italy, and evaluated their migratory performance at both an hourly and a daily scale. Hourly data (flight speed and altitude for intervals of two hours) were analyzed in relation to time of day, species and season, and daily data (distance between roosting sites) in relation to species, season, day length and tailwind support. [Conclusions/Significance]: Despite a clear variation in morphology, interspecific differences were generally very small, and did only arise in spring, with long-distance migrants (>5000 km: osprey and Western marsh-harrier) being faster than species that migrate shorter distances (Egyptian vulture and short-toed eagle). Our results suggest that the most important factor explaining hourly variation in flight speed is time of day, while at a daily scale, tailwind support is the most important factor explaining variation in daily distance, raising new questions about the consequences of possible future changes in worldwide wind patterns.Satellite tracking studies were supported by the Swedish Research Council (Swedish birds, grant to TA), Terra Natura Foundation and Diputación de Alicante (Spanish birds), and Parco Gallipoli Cognato Piccole Dolomiti Lucane (Italian birds). UM is supported by a FPU grant of the Spanish Ministerio de Educación (reference AP2008-0947) and carried out this research during a stay at the Department of Biology and Centre for Animal Movement Research (Lund University, Sweden). RHGK was supported by a postdoctoral grant from the Swedish Research Council. RL has a postdoctoral grant (reference 10/12-C) co-funded by “Consejería de Educación y Ciencia” (JCCM) and the European Social Fund. PLL is supported by a “Juan de la Cierva” postdoctoral grant of the Spanish Ministry of Economy and Competitiveness (reference JCI-2011-09588). DP is awarded with a grant from the Research Foundation of The University of Helsinki.Peer Reviewe