VARIATION OF NESTLING DIET ACROSS THE BREEDING SEASON IN SPANISH SPARROW PASSER HISPANIOLENSIS IN SOUTHERN PORTUGAL VARIACIÓN DE LA DIETA DE LOS POLLOS DURANTE EL PERIODO REPRO- DUCTOR EN EL GORRIÓN MORUNO PASSER HISPANIOLENSIS EN EL SUR DE PORTUGAL

of the Palaearctic sparrows (Summers-Smith, 1988), nesting in very dense tree colonies, both in other birds nests and in man-made structures (Sacarrão & Soares, 1975; Alonso, 1984; Metzmacher, 1990). The nesting in colonies is highly synchronised (Alonso, 1984; Metzmacher, 1990), with 75% to 89% of the nests first egg being laid within 5 days (Gavrilov, 1963; Marques, 2002). In this study we report on the diet of the nestlings of Spanish Sparrow and analyse the variation of the diet composition within the breeding season. Information about a species’ food habits is fundamental for the understanding of its ecology. This knowledge is particularly important in species with impact in human activities. The Spanish Sparrow Passer hispaniolensis is mainly a seedeater (Alonso, 1985) that can become a serious problem in cereal cultivation in semi-arid areas (Gavrilov, 1963; Mirza et al., 1975; Metzmacher, 1983; Summers-Smith, 1988). Estimations of high levels of damage have been reported in cereal crops in Libya and Kazakhstan (Mirza et al., 1975; Gavrilov et al., 1995). The nestling diet of this species has been studied in North Africa, Algeria (Metzmacher, 1983) and Libya (Mirza et al., 1975) and in Kazakhstan (Gavrilov, 1963). Only Metzmacher (1983) presented detailed results on the composition of nestlings’ diet. In these studies the invertebrates are the prey most consumed by nestlings (ranging from 75% and 90% of the weight), while vegetable items are less important. Inversely, in adult birds the vegetal fraction is the most important (Gavrilov, 1963; Mirza et al., 1975; Alonso, 1982; Metzmacher, 1983). The study was carried out in May and June 2000 in Castro Verde, Southern Portugal (37° 41′N, 08°03′W). The Castro Verde region is a cereal crop steppe, alternating with fallow grounds, which are usually grazed by sheep and cattle. The sparrows nest in the small Eucalyptus spp. plantations and olive groves that abound in the area. Diet samples were obtained using the ligature method, which consists in applying a constricting band around the neck of nestlings with sufficient pressure on the proventriculous to prevent them from swallowing food items brought to the nest by the parents, but loose enough to avoid strangling (Kluijver, 1933). This method has a wide use to analyse the nestling diet (e.g. Henry, 1982; Martinez et al., 1992; but see Moreby & Stoate, 2000). In our study, the ligature was a plastic electric cable tie, as described by Mellott & Woods (1993). The ligature remained around the nestlings’ neck for a period of time ranging between 55 and 95 minutes (64.6 ± 1.2 minutes) after which food items were removed. The nestlings from which food was taken were compensated with insectivorous bird ration. Food was collected from 41 nests (corresponding to 157 nestlings) with ages ranging from 5 to 10 days in three different colonies. Collected items were preserved in a solution of ethanol (70%) and later identified in the laboratory to the family level. For biomass estimates (g dry weight), the samples were placed in an oven at 70°C for 48 hours and later all items of each prey type were weighted on a Ardeola 50(1), 2003, 71-75