Censusing owls in large areas: a comparison between methods

Full article

Published:

Volume 45(1), June 1998. Pages 47-53.

Language:

English

Keywords:

broadcasting methods, censusing methods, distribution, owls, Strigiformes.

Abstract:

The aim of this work is to obtain an efficient technique for censusing owls in large areas. Up to now, most census works on this group have been carried out by means of enquiries combined with nest site or territory searches. This study added the broadcasting method and tested the efficiency of the three methods. We carried out an intensive census of nocturnal raptors in Biscay (Northern Spain) during four years (1992-1996). In this time we used three different methods: 1- searching for suitable owl nest sites, 2- enquiries to rural people and colleagues, 3- broadcasting methods. We found that the broadcasting method was most efficient for censusing Tawny Owls (Strix aluco), Little Owls (Athene noctua) and Barn Owls (Tyto alba). The response of Tawny and Little Owls to broadcasts did not vary throughout the year and was not influenced by weather conditions. However, responses by Barn Owls varied significantly throughout the year, being March, April, May and July the best months for censusing this species with broadcasting methods. Moreover, the territorial behaviour of this species was influenced by weather conditions. The two other methods allowed us to obtain some data that complemented the results obtained by broadcasting methods, and were necessary to find some secretive and scarce owls like Long-Eared Owls and Eagle Owls. On the basis of these results, the used broadcasting methods as the main technique for censusing owls and for monitoring their populations is strongly advisable. However, it must be complemented with the two other methods to obtain complete results for all owl species.