Searching for potential wintering and migration areas of a Danish Barn Swallow population in South Africa by correlating NDVI with survival estimates

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

“…Several studies on migratory birds have pointed out that the ecological conditions they face during a period of their annual cycle may have carry-over effects on their performance in later stages. 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).…”

“…Our fragmentary knowledge of the ecology and distribution of aerial insectivores, such as swifts and martins, during migration and in the wintering grounds, is likely a result of their strict aerial behavior, which limits the application of common field methods (e.g., ringing recoveries) to these species (Calvert et al 2009a). Importantly, in the Eurasian-Afrotropical migration system, stable isotope distribution is poorly documented, thus currently precluding tracking the origin of migrants using the isotopic signature of, e.g., feathers (Webster et al 2002, Szép et al 2006, Hobson and Wassenaar 2008, Larson and Hobson 2009, Szép et al 2009). The development of new technological devices may bridge this gap in our knowledge about the migration of small to medium sized birds in the near future (Stuchbury et al 2009, Bachler et al 2010.…”

“…The theoretical and methodological principles underlying this procedure were first proposed by Szép and Møller (2005) and Szép et al (2006). Assuming that the survival rate of individuals of the population under scrutiny is mainly driven by conditions during wintering, they argued that potential wintering grounds of a population might be identified as those areas where year-to-year fluctuation in some general indices of environmental conditions correlate most strictly with year-to-year variation in population consistency observed at the breeding grounds.…”

“…Assuming that the survival rate of individuals of the population under scrutiny is mainly driven by conditions during wintering, they argued that potential wintering grounds of a population might be identified as those areas where year-to-year fluctuation in some general indices of environmental conditions correlate most strictly with year-to-year variation in population consistency observed at the breeding grounds. Despite the large degree of uncertainty in the results and the call for validation through independent methods (e.g., ring recoveries), the approach of Szép and Møller (2005) and Szép et al (2006) is the only one applicable to species whose ecological characteristics have prevented the collection of large datasets of ring recoveries by common fields methods. As an index of environmental conditions, Szép and Møller (2005) and Szép et al (2006) used the Normalized Difference Vegetation Index (NDVI), a general index of primary productivity that, in turn, determines secondary productivity in general and availability of flying insects in particular and, therefore, may affect winter mortality and population size of aerial insectivores (Saino et al 2004, Szép et al 2006, Giralt and Valera 2007, Balbontin et al 2009).…”

“…Here, we propose to implement the procedure proposed by Szép and Møller (2005) and Szép et al (2006) to infer wintering grounds of populations based on a time series of indices of population size, such as those commonly obtained from extensive long-term bird monitoring schemes, so that information on the potential wintering grounds of a large number of populations can be quickly obtained from data already collected in the field. This information may be of importance for planning effective conservation strategies for declining species, although such results do need to be validated with independent evidence about the presence of birds from the population under scrutiny.…”