When neighbours are not ‘dear enemies’: a study in the winter wren, Troglodytes troglodytes

Owing to the cost of territorial behaviour, territorial animals are able to adjust and modulate the intensity of their response according to their own condition and to the identity of the intruder. In birds, when neighbouring territorial males are well established, they often show a less intense response towards known neighbours than towards stranger conspecific males, a phenomenon known as the ‘dear enemy’ effect. Through playback experiments performed at the beginning, the middle and the end of the breeding season, we showed that winter wren males were able to discriminate neighbour versus stranger territorial songs despite a partial sharing of syllable repertoire. Surprisingly, males showed a stronger response to neighbours at the beginning of the breeding season and reacted as strongly to neighbour and stranger songs afterwards even if they lived in groups of stable and well-established neighbours. This suggests that neighbours can be as threatening as strangers, probably in both contexts of territorial occupancy and mate attraction, and that interactions between neighbours may depend on multiple factors including ecological constraints, past experiences and mating systems.