Zoologists from Oxford University have discovered that in feral chickens, a battle of the sexes can ruin a rooster's chances of reproducing. While feral males may still dominate the act of mating itself, the hen is not completely without choice. If she doesn't deem the rooster worthy enough, researchers say that the hen has a secret weapon which challenges, and in many cases, cleverly thwarts, an unfavorable mate's chance of paternity.
All hens put up and shut up
Hens have few choices when it comes to breeding. Pinned down and rendered incapacitated, a hen is subjected to the whim of whichever cockerel wishes to mate with her. In many domestic flocks, unless breeding is the primary purpose, flock ratios favor hens more than roosters, leaving the poor female chicken to make do with whichever schmuck is on hand. Not so in feral flocks say Zoologists, where the hen is offered more choices and holds the power to deny paternity.
The Oxford University's study into feral chickens, published in the August edition of the American Naturalist, discovered that when a less-than-favorable male mated with a hen, she simply ousted the sperm immediately after mating. In a press release, issued by Oxford's, Pete Wilton on August 02, Wilton reports that when hens do decide to reject the ejaculate, on average, 80% of it is expelled. But to what purpose?
Chicken bias influences paternity
Rebecca Dean, of Oxford University's Department of Zoology, indicates the reasoning behind the feral hen's ability, is selection and preference, even though she has no actual say in which rooster mates with her. Hens have their favorite partners, typically first loves, whom they choose over newer mates. Quite naturally, the best and more dominant roosters were less likely to be ejected, but roosters depositing large amounts of ejaculate, faced a higher than normal risk of being ejected.
Even though feral hens are not successful in ejecting 100% of the ejaculate, if a hen breeds several times after the initial unwelcome breeding, sperm count from the unwanted mating is reduced and outnumbered, by the ejaculate of her preferred rooster. With sperm count significantly diminished, the unfavored rooster has less chance of fertilizing her eggs.
Dean told Wilton, ‘Sperm ejection imposes on males an evolutionary dilemma. This trade-off between ejection risk and amount of sperm ejected could generate opposing selection on the evolution of sperm allocation strategies in males."
This isn't the first time that ejection of ejaculate in chickens has been studied. In 2000, a pair of British researchers observing free-ranging chickens in Sweden, described how hens squirted semen back onto the rooster before he could even pull away.
Interestingly, in the time it takes a rooster to mate, (1-2 seconds), the female chicken has completed her evaluation, and already knows whether she'll accept him, or reject him. Don't ever say, that a female is incapable of making her mind up.
Sources (accessed Aug. 10, 2011):
- Wilton, Pete. "Hens' Sperm Ejection Secrets," University of Oxford. Ox.ac.uk. Aug. 02. 2011
- Winstead, Edward. R. "Hens Eject Sperm; Roosters are Clueless." Genome News Network. Genomenewsnetwork.org. June 16, 2000
Elizabeth Batt - Elizabeth Batt is a former large animal nurse, certified NREMT, lover of equines and conservationist.
