SUMMARY This paper presents the first extensive evidence of vocal imitations of African birds by a Palaearctic migrant, the Marsh Warbler Acrocephalus palustris. Nearly 30 individual tape recorded repertoires have been analysed, most of them from Belgium; imitations of each identified species were compared to models by spectrographic analysis. A list of 113 African species (33 non‐passerines, 80 passerines) was thus established (Appendix), which, added to the list of 99 European species, gives a total imitative range of 212 species. The low‐pitched voices of many non‐passerines exclude them from imitation. Vocal imitations of some rather local species in East Africa provide information on the localization of the autumn and winter quarters of A. palustris. In particular, the frequency of imitations of such species as Vinaceous Dove Streptopelia vinacea, Boran Cisticola Cisticola bodessa and Red‐pate Cisticola C. ruficeps lends support to the idea of the existence of autumn quarters in northeastern Africa. Individual repertoires contain an average of 76.2 different imitated species (extremes 63–84), the number of African species (average 45.0) exceeding that of European species (average 31.2). About a fifth of the complete song remains unidentified and probably corresponds to imitations of African birds whose voices have not yet been recorded. The most recurrent imitations are those of noticeably noisy species, widespread in Africa. A. palustris appears not to be selective in its repertoire. Imitations of different species can, to some extent, be combined and alternated into original motifs. Circumstantial evidence indicates that the young A. palustris are still learning song motifs when on their way to their winter quarters and probably stop learning soon after their arrival there, most of them in January, at the age of 6–7 months. There is a temporal separation between the sensitive phase and the motor phase of song learning. No conclusion as to the possible functions of the imitative element of the song can be drawn at present.
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.
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