Population estimates and distribution changes of landbirds on Silhouette Island,Seychelles

Cresswell, W., Irwin, M., Mee, A., Mellanby, R., McKean, M. & Milne, L. 1997. Population estimates and distribution changes of landbirds on Silhouette Island, Seychelles. Ostrich 68 (2–4): 50–57.

The density of landbird species within different habitats, and presence within 4 ha squares, on Silhouette Island were recorded in August 1996, repeating a previous survey (January 1979). Densities of the four most common species were calculated from point counts: Seychelles Sunbirds occurred at 2–5 birds/ha, Seychelles Bulbuls 0.5–4 birds/ha, Indian Mynahs 0.2–2 birds/ha and Seychelles Blue Pigeons 0.3 birds/ha depending on habitat. Population estimates were: Seychelles Sunbirds 5600, Seychelles Bulbuls 4000, Indian Mynahs 1100, Seychelles Blue Pigeons 600, and Seychelles Kestrel, approximately 15 pairs. The distributions of non-endemic Indian Mynahs, Barred Ground Doves and Madagascar Fodies were smaller in 1996 compared to 1979, while those of endemic Seychelles Bulbuls and Sunbirds were larger. Mynahs were more likely to occur in squares containing human activity, but habitat variables rather than human effects predicted the presence or absence of endemics. Mynahs were more likely to occur in a square, controlling for habitat variables, if Bulbuls were absent, and vice versa. There may be major seasonal changes in the relative distribution of introduced and endemic species. Alternatively, introduced species may have actually declined, probably because of a decrease in human population between the two surveys; endemics may then have increased because of reduced competition.