Relative threat and recognition ability in the responses of tropical mockingbirds to song playback

Abstract

It has been suggested that individual recognition based on song may be constrained by repertoire size in songbirds with very large song repertoires. This hypothesis has been difficult to test because there are few studies on species with very large repertoires and because traditional experiments based on the dear enemy effect do not provide evidence against recognition. The tropical mockingbird, Mimus gilvus, is a cooperative breeder with very large song repertoires and stable territorial neighbourhoods. The social system of this species allowed us to test individual recognition based on song independently from the dear enemy effect by evaluating male response to playback of strangers, neighbours (from shared and unshared boundaries), co-males (i.e. other males in the same social group) and own songs. Although subjects did not show a dear enemy effect, they were less aggressive to co-males than to all other singers. Our results suggest that recognition in tropical mockingbirds (1) does not simply distinguish between familiar and unfamiliar singers, (2) requires a small sample of both songs and song types, (3) does not rely on individual-specific sequences of song types and (4) is not likely to rely on group-specific vocal signatures potentially available in cooperatively breeding groups. We conclude that this is a case of true recognition and suggest that the lack of a dear enemy effect in this and other species with large repertoires may relate to the role of song in mate attraction and the perception of neighbours as a threat to future paternity.

Figure 1

Four typical songs of a male tropical mockingbird from Villa de Leyva, Colombia. Each song represents a different song type, based on differences in syllable (sensu Wildenthal 1965) composition.

Figure 2

Least squares means ± SE for weak- and intense-response scores during playback trials (see Table 3 for pairwise comparisons). Playback treatments as in Table 1.

Figure 3

Nonparametric cumulative failure plots (Kaplan-Meier method) for (a) the latency to sing and (b) the latency to approach. The profile for each line reflects the cumulative percentage of subjects that sang or approached within a given time frame. Playback treatments as in Table 1. B stands for the bird’s own-songs treatment.