The influx of Red-footed Falcons Falco vespertinus in Slovenia in spring 2015

The Red-footed Falcon Falco vespertinus is widely distributed from eastern Europe to north central Asia, with its main European breeding populations (in descending order of size) in Russia, Ukraine, Romania and Hungary (Ferguson-Lees & Christie 2001, BirdLife International 2015). The species is a long distance migrant wintering in southern Africa from Angola and Zambia to northern South Africa (Ferguson-Lees & Christie 2001). It is known to migrate in a loop: flying along a broad front through the eastern Mediterranean in autumn and following a more westerly route in spring (Glutz von Blotzheim et al. 1989). Influxes of the species into western and central Europe are known to occur particularly in spring, when migration coincides with anticyclonic systems in eastern Europe (FergusonLees & Christie 2001). Meteorological conditions further south along the species' migration route could conceivably also play a role in these influxes, even though this hypothesis remains unproven. Recent large spring influxes took place in 2008 (Mayer & Kratzer 2009, Volet & Gerber 2009) and 1992 (Hagemeijer 1994, Nightingale & Allsopp 1994). In Slovenia, the species occurs regularly on migration, much more commonly in spring than in autumn (Tome et al. 2005, Bordjan & Božič 2009, Bordjan 2012). The spring migration of the species lasts from late April to early June with a peak in mid-May (Tome et al. 2005, Bordjan 2012). Based on limited data, the number of migrating Red-footed Falcons through Slovenia in spring was estimated at 500–2000 individuals (Denac et al. 2011). The highest numbers were observed at Lake Cerknica and Ljubljansko barje with highest daily counts of 1000 (Bordjan 2010) and 42 individuals (Tome et al. 2005), respectively. The seasonal totals are estimated at 300–1500 individuals