Orthopteran prey sources of Red-footed Falcon (Falco vespertinus) on grasslands near their nesting sites in Serbia

Red-footed Falcons (Falco vespertinus) in the breeding period feed mainly on orthopteran insects. Theoretically, the availability of this food source may affect the size of the colonies of nesting birds and breeding success. We hypothesized that in the grassland habitats around larger colonies, sources of the orthopteran prey are richer in quality and quantity than around smaller colonies or solitary nests. Furthermore, we predicted that during the growth of the nestlings, the individuals of orthopteran species that are potential prey also grow over time. Orthopteran assemblages living in grasslands near 19 Red-footed Falcon nesting sites were sampled with sweep-nets in the northern province of Serbia, Voivodina, in June and July 2003. A total of 1,454 individuals of 25 Orthoptera species were identified in the study area, 21 species from the samples in Bachka (region between the Danube and Tisa River), while 24 species were collected in the Banat (areas east of the Tisa River). Individuals of larger orthopteran species were found only sporadically. At the same time with growths of Red-footed Falcon nestlings, from June to July, neither the potentially available orthopteran species nor the number of their individuals changed significantly. The body length of the most common orthopteran species Common Straw Grasshopper (Euchorthippus declivus) was significantly larger in July than in June. We could not detect relationship between the size of the Red-footed Falcon colonies and the number of species and individuals of the orthopterans. The proper management and conservation of these overgrazed and degraded grasslands should be a priority task, since these are hunting areas for Red-footed Falcons and at the same time, the habitats of several rare and in Serbia protected Orthoptera species e.g. Steppe Spiny Bush-cricket (Gampsocleis glabra), Veysel’s Slender Bush-cricket (Tessellana veyseli) and Cone-headed Grasshopper (Acrida ungarica).