The relative importance of conditions in wintering and passage areas on spring arrival dates: the case of long-distance
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ORIGINAL ARTICLE
The relative importance of conditions in wintering and passage areas on spring arrival dates: the case of long-distance Iberian migrants Oscar Gordo Æ Juan Jose´ Sanz
Received: 10 April 2007 / Revised: 11 October 2007 / Accepted: 8 November 2007 / Published online: 27 November 2007 Ó Dt. Ornithologen-Gesellschaft e.V. 2007
Abstract Remote sensing data have been used in previous studies to assess the effects of winter ecological conditions in Africa on biological parameters recorded in bird populations during the following breeding season in Europe. Based on the results of these studies, we hypothesized that a high productivity of vegetation during the winter and, thus, high resource availability, should advance the arrival of long-distance migrants to the European breeding areas due to enhanced ecological conditions. To test this hypothesis, between 1982 and 2000 we examined the first arrival date to the Iberian Peninsula of five species (White Stork, Cuckoo, Common Swift, Barn Swallow and Nightingale) in relation to several explanatory variables: ecological conditions in their African wintering grounds and passage areas, as reflected by the normalized difference vegetation index (NDVI), temperature and precipitation in their passage areas and the winter North Atlantic Oscillation (NAO). Ecological conditions in the wintering areas were important for White Stork, Cuckoo and Barn Swallow phenology, while both NDVI in passage areas and NAO did not have an effect on any species. Migratory birds arrived earlier after winters with high vegetation productivity in Africa. Temperature in passage areas was important for the later species (i.e. Cuckoo, Common Swift
Communicated by F. Bairlein.
Electronic supplementary material The online version of this article (doi:10.1007/s10336-007-0260-z) contains supplementary material, which is available to authorized users. O. Gordo (&) J. J. Sanz Departamento de Ecologı´a Evolutiva, Museo Nacional de Ciencias Naturales (CSIC), C/ Jose´ Gutie´rrez Abascal 2, 28006 Madrid, Spain e-mail: [email protected]
and Nightingale), although in all cases the true relevance of this factor was scarce due to the poor explanatory capacity of the models. These species were recorded in the Iberian Peninsula earlier in the spring of those years with warmer temperatures in passage areas. The nexus between African NDVI and arrival phenology is hypothesized through increases in wintering survival rates and/or the faster acquisition of pre-migratory body condition and progression through sub-Saharan areas. Keywords Africa Bird migration Climate Iberian Peninsula NDVI Phenology
Introduction Trans-Saharan migratory birds spend part of their life cycle south of the Sahara Desert (Moreau 1972; Curry-Lindahl 1981). Despite the time spent in these areas, the winter ecology of these species is still rather poorly understood. This problem is accentuated for most of the smaller bodied birds because basic information on their wintering distribution is still scarce or non-existent (
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