Falco eleonorae and its importance for coloniality

Pellets near nests and insect fragments in nests of Eleonora's Falcon Falco eleonorae in Crete were collected and used to analyse the insect diet. Results are compared with other respective data across the species' range. The hunting behaviour on small and large insects in flight is described and discussed as to its importance for communal feeding, gregarious roosting, and coloniality in falcons. INTRODUCTION Several small falcon species feed on insects to a large extent (del Hoyo et al. 1994). But also large falcons such as the Peregrine Falco peregrinus catch and eat insects occasionally (Rockenbauch 2002). Eleonora's Falcon Falco eleonorae is an aerial predator of fairly large size which feeds on insects in its wintering quarters in East Africa and the adjoining Indian Ocean islands and primarily on insects in its breeding range in the Mediterranean basin and western Atlantic during spring till July/August. At this time of year the diet gradually shifts to small migrant birds caught above the sea, close to the breeding colonies on cliffs (Walter 1979). Some late passerine spring migrants are preyed upon, too, as is implied by bird remains in seven out of 26 stomach contents obtained during May-July (Vaughan 1961). When analysing the causes for secondary or inadvertent poisoning in this species (Anonymous 2002; Ristow 2001), it is essential to have a reference list on its diet. There are quite a few lists on captured bird prey in autumn e.g. Ristow et al. (1986) for Crete, Spina et al. (1987) for Italy, Mayol (1976) and Araujo et al. (1977) for Spain, Walter (1979) and Clark (1981) for Morocco. But there is not a similar status of knowledge on insect diet which is reviewed in Tables 1+2. These data were extracted from the literature given at the end of 1 This contribution represents part 26 of a series on Eleonora's Falcon 705 this paper and from personal communications. They represent a compilation of scattered and unsystematically obtained data; the best list was published by Araujo et al. (1977). This contribution is no marked step forward, but aims to stimulate the discussion about the social aspects of bird and insect hunting. MATERIAL AND METHODS The pellet study was carried out in a large colony of Eleonora's Falcon on an islet off Crete in 1997, general prey study at nests in Aug.-Oct. 1988. Perch sites are typically a few metres away from the eyrie. Below them, up to twenty pellets may be piled up. Some fall apart like chaff when touched, others have already fallen apart when vomited, and several digestive stones are found at the site. Complete pellets from one site were carefully collected into a small plastic bag and a paper slip was added with a note about the number of pellets containing feathers, beetles, ants, cicadas, or a mixture of them, as could be judged from pellet surfaces. Except for those with feathers, pellets tended to fall apart during transport later on. The analysis showed that the digestive stones did not mill ant or beetle fragments to powder, whereas remains of moths, butterflies and dragonflies were completely digested. RESULTS As there was no rain in May-July 1997, the results refer to this whole season. Only about 10% of the pellets contained uniform prey types, whereas usually they consisted of some mixture. Thus • 21 with bird remains • 72 with beetles • 119 with cicadas • 132 with ants in a total of 205 pellets were found. A few contained grasshoppers (Saltatoria); in two pellets there were no wings amongst the ants. The beetle fragments could be determined to a somewhat better accuracy in a few cases: Coleoptera: Carabidae, Carabus sp. , Calosoma sycophanta • Dytiscidae Agabus sp. • Staphylinidae • Elateridae Elaterferrugirteus • Buprestidae at least three species; Calcophora • Scarabeidae • Geotrupinae • Melolonthinae • Cetoniinae at least two species; Potosia sp. As a supplement to the above , eight stomach contents of dead falcons from the same colony are given. Although the carcasses were found in September 1999-2001, the date of death was estimated to be in July. Four stomachs were full with cicadas, one with Buprestidae, one with dragonflies, and two were empty. Stomach contents were more uniform than pellet contents. From August onward fresh pellets contain feathers primarily. During incubation of the eggs, the female plucks birds, brought by the male, in the vicinity of the nest. When the chicks have hatched, bird pluckings can be collected in the eyrie. Only very few insect fragments are found in the nests then, and their numbers decline with season (Column k Table 3). These insects