Population ecology, food and conservation of the Seychelles kestrel (Falco araea) on Mahé
A study of the endemic kestrel on the island of Mahe in Seychelles was carried out over three years, 1975-77. Emphasis was placed on population dispersion, breeding biology, food and conservation. Kestrels occupied exclusive home ranges which were actively defended and nest sites were significantly over-dispersed. Removal experiments demonstrated the existence of a non-breeding surplus. Egg-laying occurred each year between August and October and one brood was reared per annum. Laying occurred consistently at a time of increasing food availability and young were in the nest when food availability was at a maximum. Clutch size was two or three, incubation lasted 30 days, the nestling period 38 days and the post-fledging period 9-24 weeks. In upland areas (> 200 m) 68% of pairs nested In cliffs and the remainder in trees. On the coast 44% used coconut palms, 27% cliffs, 17% trees and 12% buildings. Only 18% of pairs nesting in palms fledged young compared with 35% in buildings, 67% in trees and 75% in cliffs. This difference was attributed to differences in predation levels reflecting relative 'insecurity' of nest sites in palms and buildings. Overall breeding success in 1977 was significantly depressed compared with 1975 and 1976. This was attributed to food shortage in 1977. Kestrels occupied a range of habitats from open-country to mixed forest and took prey from the ground and throughout the full vertical range of vegetation. In terms of 'number of items' vertebrates comprised 56% and invertebrates (exclusively insects) 44% of the diet. Lizards constituted 92% of the vertebrate component, with the green gecko (Phelsumo) 67%, and the ground skink (Mabuya) 31%. In terms of 'biomass' lizards comprised 70%, 'other vertebrates' 20% and Insects 10%. In the last 100 years the kestrel has become extinct on the islands in the Praslin-La Digue group and yet has survived on Mahe, Silhouette and adjacent islands which together have a contemporary population of about 420 pairs. The low breeding success caused by high levels of predation at coastal sites on Mahe was considered insufficient to sustain populations of kestrels without a continual influx of young from upland areas. Such upland areas (and therefore reservoirs of high breeding success) are much fewer on the Praslin-La Digue group and this is considered to be, at least part of the explanation for the extinction of kestrels on Praslin-La Digue.