Zur biologischen Bedeutung des Estrildidengesanges

Zusammenfassung

Viele Prachtfinken (Estrildidae) tragen außerhalb der Balz einen „ungerichteten Gesang“ vor. Diese Gesangsform scheint primär mehr oder minder funktionslos und lediglich Ausdruck einer besonders ausgeglichenen Stimmungslage zu sein. Sekundär kann sie infolge großer intraspezifischer Modifikationsbreite ein persönliches Erkennen des ♂'s gewährleisten und durch verschiedenartige Anpassungen (Gruppengesänge, Entwicklung des „Zuhörens“, Gesangshemmung in Partnernähe mit anschließendem Ablauf intensiver Paarbindungszeremonien) auch die Paar- und Gruppenbindung festigen. Mit dieser Zunahme der „sozialen“ Funktionen wird der Gesang gleichzeitig von der Keimdrüsenreifung immer unabhängiger und ist bei drei der beobachteten Arten (Uraeginthus angolensis, Lagonosticta rhodopareia undAmadina erythrocephala) selbst bei völlig inaktiven Gonaden voll ausgebildet. Auf diese Weise kann er seine sozialen Aufgaben ganzjährig erfüllen.

Summary

Many species of Grass Finches (Estrildidae) sing not only during court-ship (“display song“) but also on numerous other occasions (“solitary song“). In general the solitary song does not seem to possess any significant biological function seeming rather to be just a sign of a very tranquil mood, not influenced by any other motivation. In some species, however, it has acquired several new, “social“ functions: Due to its remarkably great individual variability the song of the ♂ may contribute to individual recognition within a pair or a breeding colony. It may also promote pair and flock cohesion. In connection with this, several behavioural adaptations have arisen such as singing in duos and trios or “peering” at the singer by other members of the flock.

In theLagonosticta andUraeginthus species males and females possess a song. Solitary song, however, seems to be inhibited by the presence of other birds of the same species, especially the bird's own mate. For this reason the birds are forced to separate from each other for the utterance of solitary song. After having ceased singing they usually come together again and will go through their special greeting ceremonies — the stimulating and synchronizing properties of which are well known — with especially high intensity. Solitary song may thus contribute indirectly to cementing the pair bond.

In all species in which solitary song possesses a marked “social” function it seems to have become more and more independent of gonadal development. Some species (e. g.Uraeginthus angolensis, Lagonosticta rhodopareia, Amadina erythrocephala) sing all the year round and even — as has been proved by histological examination — with completely inactive gonads (stage 1 of the testis cycle, followingBlanchard 1941). It is not clear yet whether song in these species is still sexual or partly “social” or autochthonous in motivation.

The various social functions of solitary song clearly demonstrate thatAndrew's (1961) definition of “song” seems to be an unnecessarily restricted interpretation which should be abandoned.