CAPTURE EFFICIENCY OF MIST NETS WITH COMMENTS ON THEIR ROLE IN THE ASSESSMENT OF PASSERINE HABITAT USE

Variation in capture efficiency of mist nets among species or with wea ther and habitat may affect the interpretation of mist-netting data fo r studies of habitat use and diurnal activity. Capture efficiency of m ist nets with a mesh size, of 36 mm was determined by observing birds flying towards the nets in various habitats (reed-bed, bushes, grassla nd). The proportion of birds escaping from a mist net shelf after havi ng entered it depended on the size of the species and on wind speed. S mall passerines and species as large as thrushes or larger escaped mor e frequently than intermediate-sized passerine species of 10-25 g. Str ong winds added 7-16% to the escape rates under weak winds. The propor tion of birds avoiding mist nets without entering a shelf depended on the degree of shading and net-shelf height, but not on species, wind s peed, and habitat. Birds flying towards mist nets in full sunlight or towards the top shelf avoided the net more frequently than birds flyin g towards partially or completely shaded mist nets or towards lower ne t shelves. We conclude that capture frequencies from mist netting are an adequate method for assessing habitat use of small birds, but with certain reservations: capture numbers do not represent quantitatively the species composition and all mist nets should be similarly exposed to the sun and wind (i.e., preferably in a straight line in vegetation as high as the nets).