Mixed Singing in European Songbirds — a Review

Abstract

and Summary The phenomenon of mixed singing in songbirds has recently been interpreted as one of vocal convergence facilitating interspecific competition. This paper examines the welldocumented cases of mixed singing in European songbirds with regard to the relationships between mixed singers and their models, and the frequency of occurrence of such behaviour. Mixed singers are individual members of songbird species which in their full song extensively copy vocal patterns of an alien species and reproduce them next to their own. Models are, in most cases, taken from congeneric species, usually sibling species (Table 2). A few species, however, copy totally unrelated songbirds but some structural resemblance is often found between the vocalizations of model and imitator. Mixed songs are usually rare, found in isolated individuals. Mixed songs can be adopted in some populations by a large proportion of the birds in situations of isolation or in small areas of overlap between largely allopatric species. Some mixed singers of several species remain unmated or hybridize with the model species. Discounting a small number of possible exceptions, e. g. blackcap Sylvia atricapilla and garden warbler S. borin, mixed songs are best regarded as the result of misdirected song learning. There is no justification for categorizing mixed singing as an example of vocal convergence, as has been done by Dobkin (1979). Zusammenfassung Als Mischsänger werden Singvogelindividuen definiert, die in ihrem Vollgesang regelmäßig Lautmuster einer anderen Art imitieren. Das artfremde Muster wird entweder wechselnd mit dem eigenen vorgebracht, oder beide werden zu einem einheitlichen Gebilde kombiniert. In den meisten Fällen gehören die gewählten Vorbilder nächstverwandten Arten an, normalerweise Schwesternarten (Tab. 2). Nur selten werden nicht verwandte Vorbilder imitiert, die aber strukturelle Übereinstimmungen mit dem Gesang des Nachahmers aufweisen. In der Mehrzahl der Fälle werden nur einzelne Individuen einer Population zu Mischsängern. Ausnahmsweise gibt es mischsingende Populationen oder Teilpopulationen, so bei Isolation oder in schmalen Überlappungszonen allo‐patrischer Arten. Mischsänger verschiedener Arten blieben unverpaart oder gingen eine Bindung mit der Vorbildart ein. Mit wenigen möglichen Ausnahmen (z. B. Sylvia atricapilla — S. borin) muß man annehmen, daß Mischgesang auf Tradierungsfehler beim Gesangslernen zurückgeht. Es gibt bislang keinerlei Berechtigung, Mischsingen im Sinne von Dobkin(1979) als ein Beispiel akustischer Konvergenz einzustufen.

Songs of Darwin's finches diverge when a new species enters the community

“…When introgression occurs, the species exchange one component (genes) but not the other (song). In this respect they differ from some other species where hybrids sing elements of the songs of both of the parental species (43,55). Thus in contrast to many other species of birds the defining feature of a population of Darwin's finches is a cultural learned signal.…”

The Causes and Evolutionary Consequences of Mixed Singing in Two Hybridizing Songbird Species (Luscinia spp.)

“…On the other hand, species may also converge in some features; this is often observed in bird songs (e.g., [6], [11]). The mechanisms leading to song convergence may include (1) cross-species song learning [3], [12], [13], (2) ecological adaptation to the local environment [14]–[17], and (3) genetic introgression [18]–[20]. Such convergence can be followed by broad heterospecific pairing, resulting in increased interspecific hybridization and mixing of species gene pools [21]–[23].…”

Reproductive interference via display signals: the challenge of multiple receivers

“…In contrast to this prediction, signals involved in mate attraction often converge where species co-occur (Cody 1969;Helb et al 1985;Grether et al 2009;Lackey and Boughman 2013;Tobias et al 2014). Signal convergence has been especially well documented in the songs of syntopic songbirds (oscine passerines), a phenomenon referred to as mixed singing when convergence occurs through incorporation of typical heterospecific song elements (Helb et al 1985). One explanation for mixed song is that it is a non-adaptive byproduct of an open song-learning process otherwise promoted by sexual selection on repertoire size (Helb et al 1985;Secondi et al 2011;Vokurková et al 2013).…”

“…In contrast to this prediction, signals involved in mate attraction often converge where species co-occur (Cody 1969;Helb et al 1985;Grether et al 2009;Lackey and Boughman 2013;Tobias et al 2014). Signal convergence has been especially well documented in the songs of syntopic songbirds (oscine passerines), a phenomenon referred to as mixed singing when convergence occurs through incorporation of typical heterospecific song elements (Helb et al 1985).…”

“…Signal convergence has been especially well documented in the songs of syntopic songbirds (oscine passerines), a phenomenon referred to as mixed singing when convergence occurs through incorporation of typical heterospecific song elements (Helb et al 1985). One explanation for mixed song is that it is a non-adaptive byproduct of an open song-learning process otherwise promoted by sexual selection on repertoire size (Helb et al 1985;Secondi et al 2011;Vokurková et al 2013). According to this view, a general female preference for elaborated songs overrides any costs to mixing.…”