showed that in mixed species pairs, zebra finch young are given more parental care by their conspecific parent than by the Bengalese finch parent (ten Cate 1982, 1985a), and that a correlation exists between the amount of such care and the mate preference for conspecific females (ten Cate 1984), The influence of these differences in behaviour between species can be counteracted by performing similar
experiments, but by using instead two zebra finch colour morphs, Immelmann et al (1978) raised white and grey morph birds in an aviary, with half having parents of their own colour and half the other colour. He found that both sexes directed courtship to birds of the "parental" morph, with no difference in the strength of the imprinting response
between white and grey (wild-type), In Chapter 2 of this thesis, it was clearly shown that both the song tutor choice and mate choice of male zebra finches are strongly affected by visual imprinting on the plumage colour of the parents during the period of dependence ( 0 - 3 5 days after
hatching),
Further evidence demonstrating an influence of plumage
characters on mate preference, has come from the recent work of Clayton (e.g. 1990), on the two zebra finch subspecies. In the laboratory it was found that castanotis (from
mainland Australia) and guttata (from the Lesser Sunda islands, in Indonesia) chose to mate assortatively. One of the cues that may have had a role in achieving this is male breast-band size (which is larger in castanotis)* Increasing
made such birds more attractive as mates to castanotis females,
The above studies show that visual exposure to the parents (or foster-parents) can influence mate preference or, in the case of males, song tutor preference. However, they do not reveal whether such preferences might be influenced by one parent more so than by the other. Are the appearances of the father and mother of equivalent importance to both male and female offspring?
In their studies of lesser snow geese, Cooke and his colleagues showed that the two colour phases, blue and
white, tended to mate assortatively where both parents were alike (e.g. Cooke and McNally 1974). Where the parents were of different morphs there was no consistent preference.
Also, goslings with a single male foster-parent responded in colour preference tests as clearly as those with a single female foster-parent (Mirsky 1971, in Cooke and McNally 1974). These results suggested that in this case neither parental sex was more important in determining colour preference.
Snow geese are not sexually dimorphic and, as parental
duties are shared, it is perhaps not surprising that .such a difference in imprinting could not be found. Zebra finch parents also provide equivalent levels of care for their offspring but, in contrast, do exhibit strong plumage
ri 3 - 4
more relevant for young birds to pay particular attention to characteristics of one parent, rather than to those of the other,
Clayton (1988), reared zebra finch and Bengalese finch young with mixed parents, and then presented a choice between
tutors of each species from 35 to 70 days. She found that male offspring preferred to copy songs of their own species, although a few produced hybrid songs. There was no
indication of a stronger effect when the conspecific parent was of a particular sex. With regard to sexual preference, there was a non-significant tendency for males to be more directed to conspecifics where it was the mother that was of their own species. However, both parents certainly had an influence.
Again, there is a problem here of the confounding effect of using two species, with different behaviours and vocal
characteristics. These factors make the search for an influence of imprinting on a particular parent more difficult: an overall bias for conspecifics could have resulted because a heterospecific parent provides a less effective imprinting stimulus, or because a heterospecific tutor acts in a less stimulating manner. Such effects could conceal an underlying pattern, whereby the parent of one sex might normally be more influential in the imprinting process than that of the other.
The present study was an investigation of the mate and song tutor preferences of zebra finches, when reared by parents
grey (wild-type) and chestnut-flanked white. Any behavioural differences between these morphs were certainly not
pronounced - there was an equally strong preference for the parental morph in most of the results of Chapter 2, where the parents were both alike in colour. The only exception to this equal preference occurred in the second experiment
described there, where there was sequential exposure to the two morphs. In this case, an overall mate preference for grey females resulted (it may be significant that it is under these circumstances that the influence of imprinting on the parents is likely to be weakest - see Chapter 2). Following the same general regime as for experiment 1
(Chapter 2), a choice of two tutors, one of each morph, was given from 35 days. The following questions were of
particular interest:
- would there be a mate preference for the colour morph of one sex of parent, in the case of either the male or the female offspring? If so, is it the same sex of parent that is of the most importance for both sexes?
- would male offspring have a song tutor preference for the colour morph of a specific parent (more likely the father)? If so, does this differ from that shown in mate preference tests?
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