Song-type matching between neighbouring song sparrows

In our study population, neighbouring song sparrows typically share two or more of their 6-10 song types. In an earlier experiment, we found that esta blished neighbours typically reply to playback of neighbour-shared song wit h a different song they share with that neighbour ('repertoire matching'), rather than with the same song ('type matching') or with a nonshared song. In the present experiment, we considered the hypothesis that type matching is a threat or warning signal (Krebs et al. 1981, Animal Behaviour, 29, 918 -923). We tested the specific prediction that a bird is more likely to type -match early in the breeding season when territory boundaries are new and s till unstable, and more likely to repertoire-match later in the season,once those boundaries have became well established. Birds were played a shared song of a new neighbour once early (April) and again late (June) in the bre eding season. As predicted, early in the season birds usually type-matched the playback (73% of the trials) but late in the season they type-matched o nly rarely (18%); birds never replied (early or late) with a nonshared song type. (C) 2000 nit Association for the Study of Animal Behaviour.