Understanding how birds negotiate these ecological barriers is important for our understanding of migration biology and for the conservation of stopover sites used by many bird species during migration before and after barrier crossing. Although bird migration occurs across the whole width of the Mediterranean Sea, densities are highest at its western and eastern edges, where sea-crossing is short or avoided through flight over land bridges ( Bruderer and Liechti, 1999 Newton, 2008), resulting in high densities and diversity of birds migrating throughout Israel ( Shirihai, 1996). The Negev Desert in the south of Israel is located at the northern part of the Saharo-Arabian desert belt and an approximately 200 km long north-south coastline in the west of the country borders the eastern part of the Mediterranean Sea. Israel is located at the edges of these two barriers. Most of the birds that migrate between Europe and sub-Saharan Africa face two wide ecological barriers: the Mediterranean Sea (about 550 km wide, but its width varies substantially between different areas) and the Saharo-Arabian desert belt (about 2000 km wide) which they need to cross or detour twice a year. These areas are usually characterized by high densities of migrants that may compete for limited resources ( Moore and Yong, 1991 Petit, 2000).
Stopover areas adjacent to ecological barriers are critically important for the migrants that have just completed or are preparing for a cross-barrier flight ( Petit, 2000).
Since most of the migration time is spent on refueling and resting rather than in active migratory flight ( Alerstam, 2003 Wikelski et al., 2003), the ability of the birds to accomplish the journey, as well as their survival and breeding output following migration, depend on the availability and the quality of stopover sites ( Moore et al., 1995 Calvert et al., 2009 McGowan et al., 2011). Research and conservation efforts have mostly focused on protecting breeding habitats or wintering grounds and only rarely on stopover habitats used by birds during migration ( Hutto, 2000 Marra et al., 2015 Becciu et al., 2019) although migration is the period when the risk of mortality is the highest ( Sillett and Holmes, 2002 Newton, 2006). Migratory birds have been found to steeply decline in recent decades ( Berthold et al., 1998 Sokolov et al., 2001 Sanderson et al., 2006 Rosenberg et al., 2019). Our findings substantially advance the understanding of bird migration ecology near ecological barriers and facilitate informed conservation efforts in a highly populated region by identifying a few high-priority stopover areas of migrating birds. Autumn migrants also selected sites located close to water sources.
Notably, artificial light at night strongly correlated with high densities of migrants, especially in the autumn. Bird distributions were primarily associated with broad-scale geographic and anthropogenic factors rather than individual fine-scale habitat types. Boosted Regression Tree models revealed that bird distributions differed between the seasons, with higher densities in the desert and its edge, as well as inland from the sea, during spring and a predominantly coastal distribution in the autumn. Using low elevation scans of three weather radars covering 81,343 km 2, we quantified large-scale bird departure patterns during spring and autumn (2014–2018) in between two major ecological barriers, the Sahara Desert and Mediterranean Sea. Yet, our knowledge of bird stopover distributions and their mechanisms near wide ecological barriers is limited. Stopping-over is critical for migrating birds. 2Department of Entomology and Wildlife Ecology, University of Delaware, Newark, DE, United States.1Department of Evolutionary and Environmental Biology, Institute of Evolution, University of Haifa, Haifa, Israel.Smolinsky 2†, David Troupin 1, Jeffrey J.
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