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. Keywords dear enemy effect; individual recognition; Mimus gilvus; playback experiment; song repertoires; tropical mockingbird Many animals have evolved conspecific recognition abilities that allow them to direct costly behaviours to the appropriate targets. Individual recognition allows animals to invest preferentially in their own progeny in the presence of unrelated young (Beecher et al. 1981;Seddon & Vanheezik 1993;Leonard et al. 1997;Lefevre et al. 1998;Searby & Jouventin 2003), to find their mates in crowded environments (Lengagne et al. 2004), or to preferentially display altruistic acts towards those who have helped them in the past (Wilkinson 1988;Denault & McFarlane 1995). Individual recognition is important in territorial contexts where territory owners are expected to benefit from behaving less aggressively towards stable neighbours not likely to trespass than towards strangers trying to establish a new territory (dear enemy effect: Fisher 1954). Individual recognition may also allow territory owners to determine quickly when a neighbour has gone outside its typical territorial boundaries and is likely to represent a greater threat. The ability to recognize individual conspecifics on the basis of song is thought to be widespread among songbirds (Falls 1982;Temeles 1994; Stoddard 1996). Nevertheless, a few species have shown a weak dear enemy effect (Kroodsma 1976), a similar response to neighbours and strangers (Falls & d'Agincourt 1981;Beletsky 198...

Large vocal repertoires do not constrain the dear enemy effect: a playback experiment and comparative study of songbirds

“…There are at least three reasons why large song repertoires may impose a constraint on individual recognition: (1) birds must learn more songs to facilitate discrimination; (2) each song type will be heard less frequently, creating less opportunity to learn each song; and (3) song sharing may be higher, making identity assignment more difficult (Stoddard, 1996). In contrast, other studies have found that some bird species capably discriminate between conspecific individuals despite their large repertoires (Botero, Riveros, & Vehrencamp, 2007;Hyman, 2005;Weary, Lemon, & Perreault, 1992). Additionally, two decades ago, a comparative analysis suggested that there was no relationship between repertoire size and neighbourestranger discrimination ability across 20 species of passerines of the suborder Passeri (Weary et al, 1992).…”

Syllable type consistency is related to age, social status and reproductive success in the tropical mockingbird

“…From August to December 2004 and from August 2005 to May 2006, we monitored 23 social groups of individually colour-banded tropical mockingbirds in Villa de Leyva, Colombia as part of an ongoing study on song learning and song use (Botero et al 2007). These social groups include 1.8 ± 0.20 males (mean ± SE) and 1.8 ± 0.16 females (data based on 19 groups for which molecular data is available).…”

“…Tropical mockingbirds live in cooperative breeding groups with multiple members of each sex that cooperate in the defence of a territory (Botero et al 2007; Morton et al 2004). Same-sex group members are organized in linear dominance hierarchies.…”

“…In some groups, the two highest-ranking males (i.e., the alpha and beta males) compete with each other for mating with the highest ranking female (Botero et al 2007). Both alpha and beta males build nests and sing conspicuously prior to a breeding attempt, but alpha males tend to displace betas rather than be displaced by them, to perch higher when in the same tree, and to have higher song output (Botero et al 2007). Tropical mockingbirds are multibrooded and their peaks in reproductive activity coincide with the rainy seasons (Paredes et al 2001).…”

Neighbour–stranger discrimination by Yellow-bellied Tit Parus venustulus: evidence for the “dear-enemy” effect

“…Previous studies have shown that neighbouring territorial male songbirds share more song types than those with strangers, thus facilitating recognition between them (e.g. Botero et al 2007). However, we did not find any differences in shared song type between pairs of neighbouring males or stranger males, or that focal males use more song type matches to N-treatment than S-treatment playbacks (Table 2), since neighbours share only 1 song type, and strangers share 0.3.…”