Density and breeding biology of the Barn Owl Tyto alba (Aves, Tytonidae) on the tropical island of Mayotte

Tyto alba is widely distributed on Mayotte, an island group of 374 km(2) in the Comoro archipelago. The species was studied in August 1996 (dry season ) and December 1997/January 1998 (wet season). Territorial response was hig h in December/January, and there were fledged young in August, indicating t hat breeding starts in the wet season and young fledge during the dry seaso n. The species was inventoried at the beginning of the breeding season by u sing playback of calls during point-transect counts. Breeding densities wer e high, estimated at ca. 1.03 to 2.75 territories/km(2), based on three dif ferent methods of calculation. Possible sources of error are discussed, but this method will most likely produce useful results in other situations wh ere Barn Owls respond well to playback. Breeding sites were mainly cavities in trees, but cliffs and, more rarely, buildings were also used. Breeding success seemed low: 1.62 young fledged per nest.