Space and habitat use by Red KitesMilvus milvusduring winter in the Guadalquivir marshes: a comparison between resident and wintering populations

Abstract

Differences in habitat selection, diet and behaviour of resident and wintering Red Kites Milvus milvus were studied in Doiiana National Park, southwest Spain. Adult resident Red Kites roosted at their nests, while immature residents and wintering birds gathered at communal roosts. Individuals remained on average for two consecutive nights (range 1-8) at the same communal roost. Wintering kites spent significantly more time foraging gregariously than residents. The use of the marsh was greater by wintering kites while residents more often used the forest. Wintering birds consumed more goose carrion than the residents. Wintering kites had larger core areas, moved farther from their roost sites to feed and changed foraging areas more frequently than residents. Among residents, adult females had the smallest home ranges (core area, distances travelled and time spent flying). We suggest that Red Kites wintering in Doiiana occupy the marsh because it provides high food availability, and is vacated by Black Kites M . migrans which exploit this profitable habitat during the breeding season.

Communal Roosting of Wintering Red KitesMilvus milvus(Aves, Accipitridae): Social Feeding Strategies for the Exploitation of Food Resources

“…The red kite population in Doiiana consists of birds that do not attend roost sites (adult residents that remain at their nests all year round) and other birds that regularly attend roost sites (migrants from northern Europe or non-breeding resident immatures). The residents have smaller home ranges and spend less time flying than do the migrants (HEREDIA et al 1991). Kites that attend roosts search for prey gregariously and share their prey, a pattern noticed in some passerines and believed to be related, at least in part, to the migrants' poorer knowledge of local food sources (NEWTON 1972).…”

“…We did not observe, in carcasses lasting more than 1 d, an increased number of kites on the second d. The remains of larger animals may have lasted longer, and here kites may have behaved differently, but in Doiiana in winter such carcasses are usually consumed by vultures, not kites (ALVAREZ et al 1976). Usually geese carcasses are in fact the biggest eaten by kites (BLANCO et al 1987;HEREDIA et al 1991).…”

“…Kite categories used roost sites differentially (HEREDIA et al 1991). RAs roosted at their nest site or nearby and did not attend assemblages at all.…”

“…The red kite is both predator and scavenger. Wintering birds and RY more often eat bigger prey such as geese, whereas RAs tend to eat small birds and mammals (BLANCO HEREDIA et al 1991). The 8 tagged birds using roost sites consumed sharable prey more frequently ( Table 3), but only one of the 5 RAs fed on sharable prey more often (p = 0.007, Fisher's exact probability test).…”

“…The red kite, Milwus milwus, is an average size gregarious raptor relying mainly on carcasses, an ephemeral non-evasive food (HEREDIA et al 1991). It is a likely candidate species for the mechanism of information transmission (see MOCK et al 1988).…”