Sex and chickens 

HENRY GEE

How do domestic chickens choose their mates? Do they check out only the sharpest dressers? Or do nifty moves on the dancefloor count for more? In other words, what do chickens find sexy? 

Chicken farmers with big hearts would do well to consult a report in Animal Behaviour by Marty L. Leonard and Liana Zanette of the Centre for Food and Animal Research in Ottawa, Canada. "[I]f male traits associated with female preference could be identified," they say, "breeders might increase productivity by providing females with more attractive males." 

Leonard and Zanette investigated the problem in experiments in which female fowl were invited to choose between two tempting beaux. The researchers scored who scored, and with whom, and then reviewed the evidence for consistent patterns of behaviour or morphology associated with choice. 

The results were surprising. Chicks choose their mates on the basis of one thing only – the ability of a male to perform a ritualized behaviour called 'wingflapping', in which the wings are raised above the back and flapped. They were not interested in any other form of behaviour, or on the good looks of a prospective partner. 

The results are a surprise in the light of extensive studies of mate choice on the jungle fowl (Gallus gallus murghi), the closest wild relative of the domestic chicken. These studies show that female jungle fowl choose males that have the largest, reddest combs (ornaments on the top of the head). Such secondary sexual characters are good markers for the general health of the animal and thus of potential fatherhood – indeed, there is good evidence that sick or parasitised males will have smaller, drabber combs, and so will be less likely to be chosen as mates. It could be that wing-flapping – a rather vigorous behaviour – could serve the same function. But why the difference? 

For an answer, the authors cast their eyes a little more widely, by reviewing the mechanisms of mate choice in the galliform birds in general – not just chickens, but pheasant, grouse, partridge and turkeys. Both behaviour and good looks have been associated with female preference in these birds. For example, dancefloor dexterity is rated by female sage grouse (Centrocercus urophasianus) and grey partridge (Perdix perdix), but snappy male accessories such as wattles and combs are what count in wild turkeys (Meleagris galloparvo) and rock ptarmigan (Lagopus mutus). 

But no matter what mechanism female birds use to choose mates, behaviour and morphology both seem to be associated with dominance – the position of a male in the social scale. It could be that females assess dominance by either behaviour or morphology, or both, depending on the circumstances. Some female ring-necked pheasants (Phasanius colchicus) use display traits such as spur length, but their English sisters tend to be turned on by energetic display. Perhaps the same kind of difference is being seen in chickens, as distinct from jungle fowl. After all, the researchers say, female preferences for particular traits have been known to vary from year to year, and from study to study. "Differences in results across studies may indicate a shift in female preference for particular traits under different experimental conditions or the failure to measure all features relevant to females in each study," the researchers conclude. 

Or perhaps researchers have yet to penetrate the fickle mind of a choosy chick. 

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