Introduction

CHARTER

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4.1 Introduction

It has been shown in laboratory studies that a young male zebra finch will usually produce a song closely resembling that of his father, if the latter is present during the sensitive phase (see Chapter 1). This has applied to both normally-raised birds (Bohner 1983), and to female-raised ones (Bales 1987b).

Bohner (1983) housed two pairs in the same cage, but

separated by a mesh partition. Both pairs had nest boxes, but only one pair was allowed to breed. At 40 days of age their offspring were put into a separate cage, positioned in front of the "neighbour" pair (but still within sight and sound of the parents). When the songs were recorded at 100 days, it was found that, of 11 males, nine had copied most or all of the song of the father, one had learnt all of its elements from the male neighbour and one had apparently

improvised its song (with the exception of one element). Bales (1987b) kept birds only with the mother up to 35 days, housed in a sound-proof chamber, and then introduced the father and an unrelated adult male into the cage. The birds remained in this situation for four to six months, at which stage their songs were recorded. All young males involved were found to have derived their songs wholly from the

What might have caused the father to be selected as song tutor in the above experiments? In neither case were

detailed behavioural observations made, but Bohner suggests that the feeding of the young by the parents may have been important in his work. More recently, Williams (1990) argued that the amount of parental care, including feeding,

influenced song tutor choice in the zebra finches she

studied in an aviary. It is also possible that there was an influence of parental aggression prior to 40 days, during the stage in which the young are being forced into

independence, or of the relatively higher exposure to the song of the father in the early post-hatching period, due to his greater proximity. More simply, the reason might lie with greater attention being paid to the father throughout the 100 days, because of the close bond formed with him during the period of dependence.

In B al e s’ experiment, the young had only very brief contact with the father prior to the tutoring period (the first four days of life). However, they may have learnt preferentially from him because of his relationship with the mother when they were reunited. Within hours of the introduction of the two males, Bales noted an "obvious separation" in the cage, with the mother and father re-establishing their bond, while the young generally remained in a group with the second

male. In such circumstances the father could have been

selected because of behaviour associated with pairing, such as directed song and soliciting by the female. The unpaired male did not appear to court the female beyond a short

Alternatively, the father may have been more aggressive to the juveniles, and this might have had an impact (Bales noted that the fathers had a greater tendency to defend a particular area of the cage).

Less plausible possibilities would be that the young learnt to identify features of the father’s song, or perhaps the distance call, from the period before he was removed, and were thus able to recognise him when he reappeared, at 35 days. It might even be possible that birds are genetically biassed to learning songs of one type rather than another

(Marier 1970), but it would seem highly unlikely that this could allow differentiation between the song of the father and of another normally-singing zebra finch male, especially in view of the very strong influence of learning in the song acquisition process.

In this chapter, I describe further studies on the causes of song tutor choice in such situations. In particular, I

examined whether it is the father’s relationship with his offspring that is important, or whether learning from him is simply the result of increased exposure to his song, or of his greater aggression. It is possible that the paired status of the father per se was a major factor in the

results of Bales, and so this was looked at, by using only unrelated birds. Also the effects on song learning of

for each will be presented in turn, in the order in which they were performed.

4 .2 Experiment 1 : D.q...

zebra tinches pro

Broods were housed with their parents to 35 days. Other birds could be heard, but none were visible at a distance of less than three metres. Following the protocols of Eales and of Bohner, nest boxes were left in the breeding cages after the young had fledged (this is important, because removing them when the young are about 30 days old has been shown to affect the timing of song learning; see Slater and Richards, 1990),

From 35 to 100 days, each brood was transferred to the