Autumn Irruptions of Red-Footed Falcons Falco vespertinus in East-Central Poland

Abstract

The red-footed falcon Falco vespertinus inhabiting SE Europe is known for its irruptive migrations. Here we attempt to outline the causes (weather conditions, dietary composition etc.) of the irruptions in 2014–2016 in east-central Poland. From 2004 to 2016 a total of 2873 falcons were counted during 542 observation bouts. The speeds of E and SE winds in August and September differed significantly between irruption and non-irruption years and were 1.3 km/h faster in the irruption years. Other weather factors, such as the number of days with E and SE winds, air temperature and the global North Atlantic Oscillation (NAO) and Scandinavia (SCAND) indexes, did not differ statistically between irruption and non-irruption years. The remains of 813 prey items were found in pellets collected in August and September, with a 93% dominance of insects; 84% of these were Coleoptera and Orthoptera. The irruptions of red-footed falcons in 2014–2016 may be also associated with increase in the number of breeding pairs in SE Europe.