Song learning in oscine songbirds : Tutor choice, timing, and the relationship with sexual imprinting
Appears in the following Collection
- Biologisk institutt 
AbstractBirdsong is a species-specific signal that is used in mate attraction and intrasexual competition. This thesis concerns song acquisition in two oscine songbird species, the great tit Parus major and the pied flycatcher Ficedula hypoleuca. It addresses questions such as how free-living songbirds choose their song tutors and whether learning of foreign songs can take place in adult birds, and it looks into the relationship between song learning and sexual imprinting. This was done using a method of experimental, interspecific cross-fostering, in which eggs were swapped between nests of different species. Great tits were cross-fostered to blue tits Cyanistes caeruleus, and pied flycatchers were cross-fostered to great tits and blue tits.
In oscine songbirds, young males have to learn their song from adult conspecifics, and a mechanism is needed to ensure that they choose song tutors of the right species. Early laboratory studies proposed the existence of an innate auditory template facilitating the recognition and memorization of conspecific song. However, in a number of species, males reared by heterospecifics have been found to copy songs of the foster species and thereby become mixed singers. To account for such heterospecific song learning, it has been suggested that familiarization with the social father before independence guides the choice of song tutors. However, under natural conditions, young males may grow up without a social father. A study on captive zebra finches Taeniopygia guttata has demonstrated effects of the social mother on song learning. Based on this finding, I propose a mechanism of mothermediated tutor choice, suggesting that experience with the social mother as well as the father guides the choice of song tutor in oscine songbirds. Great tits cross-fostered to blue tits include blue tit song in their repertoires. They also get sexually misimprinted, and occasional heterospecific pairs are formed between cross-fostered great tits and cross-fostered blue tits. I tested the hypothesis of mother-mediated tutor choice by letting great tits grow up with a blue tit foster mother and a great tit foster father. Males of this treatment included blue tit song in their repertoires. To control for the possibility that the males had learned the blue tit song directly from their cross-fostered fathers, we also recorded song from great tit males that were reared by conspecifics, but whose fathers had been cross-fostered to blue tits. None of these males sang blue tit song, suggesting an effect of the social mother. However, cross-fostered great tit males mated to blue tits may sing more blue tit song than those mated to great tits. Our samples were too small to separate between heterospecific song learning resulting from mother-mediated tutor choice and from exposure to blue tit song in the repertoire of the father.
Song learning shares a number of characteristics with sexual imprinting. I investigated the relationship between these two processes in great tits. I exposed cross-fostered great tit males to playback of great tit song and blue tit song inside their territory. Males that showed sexual interest in blue tit females were more likely to respond with blue tit song to playback than males that showed interest only in conspecific females. This suggests that different degrees of misimprinting may have parallel effects on song learning and sexual preferences in cross-fostered great tit males. Furthermore, the response to territorial intruders seemed to be affected by social interactions: Cross-fostered males currently associated with blue tits increased their response to playback of blue tit song whereas males currently associated with great tits increased their response to playback of great tit song through the season.
I also studied the effect of social rearing condition on song learning in pied flycatchers. Cross-fostered pied flycatchers do not seem to get sexually misimprinted. However, I found that pied flycatcher males reared by blue tits or great tits became mixed singers, uttering a combination of pied flycatcher song and the foster species’ song. Furthermore, males reared with nest mates of the foster species included tit song in a higher proportion of strophes than did cross-fostered males reared with conspecific nest mates. Hence, in pied flycatchers, growing up with heterospecific foster parents and nest mates caused a mixed choice of song tutors without affecting their mate preferences.
Some songbird species are open-ended learners and retain the ability to learn new songs throughout their lives. However, to demonstrate that a species is a true open-ended learner, it is necessary to make sure that the elements learned as adults have not been heard and possibly memorized by the birds at an early age. I performed a playback experiment to test whether the pied flycatcher is a true open-ended learner. I exposed pied flycatcher males to playback of song containing syllables that were unknown to the study area. Among the 20 subjects, one yearling and two older males had learned a foreign syllable type, supporting the hypothesis that pied flycatchers are true open-ended learners. Pied flycatcher song is believed to serve mostly for mate attraction, and possible functions of adult song learning are to increase the repertoire size and to increase syllable sharing with neighbours. The subjects showed no increase in either of these parameters after the treatment. An alternative adaptive value of adult song learning in pied flycatchers may rather be to pick up particularly attractive song elements.
List of papers. Papers I - IV are removed from the thesis due to copyright restrictions
Paper I: Eriksen A, Slagsvold T. Mother-mediated tutor choice – an experimental study on song acquisition in wild great tits. Manuscript.
Paper II: Eriksen A, Lampe HM, Slagsvold T. Song learning and sexual misimprinting in crossfostered great tits. Manuscript.
Paper III: Eriksen A, Lampe HM, Slagsvold T. 2009. Interspecific cross-fostering affects song acquisition but not mate choice in pied flycatchers, Ficedula hypoleuca. Animal Behaviour 78: 857-863. doi:10.1016/j.anbehav.2009.07.005
Paper IV: Eriksen A, Slagsvold T, Lampe HM. 2011. Vocal plasticity – are pied flycatchers, Ficedula hypoleuca, open-ended learners? Ethology 117: 188-198. doi:10.1111/j.1439-0310.2010.01864.x