The relative importance of conditions in wintering and passage areas on spring arrival dates: the case of long-distance Iberian migrants

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 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.

Demographic response to environmental variation in breeding, stopover and non-breeding areas in a migratory passerine

“…non-breeding area or at stopover sites (Marra et al 1998;Norris et al 2004;Saino et al 2004a, b;Gordo and Sanz 2008;Harrison et al 2011). Such carry-over effects are likely to be induced by physiological constraints (Harrison et al 2011).…”

Identification of Putative Wintering Areas and Ecological Determinants of Population Dynamics of Common House-Martin (Delichon urbicum) and Common Swift (Apus apus) Breeding in Northern Italy

“…Indeed, it is known that conditions in the wintering grounds and en route affect winter and migration survival (Szép and Møller 2005, Stokke et al 2005, Szép et al 2006, Calvert et al 2009a and, therefore, the number of breeding pairs in the following year (Giralt and Valera 2007). As well, they influence the spring arrival date (Gordo et al 2005, Gordo et al 2007, Gordo and Sanz 2008, Balbotin et al 2009), physiological condition of breeding individuals (Marra et al 1998), and breeding performance in general (Saino et al 2004, Smith andMoore 2005). By studying migratory birds in only one period and one area, ornithologists obviously introduce biases in their comprehension of the ecological determinants of variations in population size, which are primarily attributed to our general scant knowledge of the actual wintering grounds and migration routes of the vast majority of small-sized species.…”

Why are bird migration dates shifting? A review of weather and climate effects on avian migratory phenology

“…Nevertheless, there are still few studies that have employed remote sensing, and only two have related arrival dates to NDVI (Saino et al 2004b, Gordo & Sanz 2008. Furthermore, most studies are focussed on a few Danish and Italian populations of a single species (the barn swallow).…”