Sunday, May 01, 2011

Science Sunday: Vain As A Peacock

Among my more interesting acquaintances over the years was Percy, an Indian Blue Peacock. Percy arrived at the farm where I long lived from an Iowa hatchery as a week-old ball of fuzz. Within months, he had matured into what is surely one of the most magnificent of birds with iridescent blue-green plumage, a train of highly elongated tail coverts with eye spots and a crest resembling a delicate if tiny tiara upon his tiny head.

The adage "proud as a peacock" is a bit of a misnomer. "Vain as a peacock" is more like it, and Percy displayed all of the attributes of his breed. This included displaying mating behavior that included fanning out his coverts (they're not feathers in the traditional sense) and shaking the brown feathers beneath them as in opening and closing venetian blinds.

The trouble was, Percy didn't have a mate and would spend endless hours doing his mating dance before chrome bumpers of an old Volvo that reflected his image or for the benefit of one of the farm cats to whom he took a fancy. We eventually put a big mirror at one end of the garden for him and then took the logical step: We got him a peahen.

Like Percy, Priscilla arrived as a week-old ball of fluff and like Percy matured into a magnificent bird, albeit with the tiara but without the riot of colors protruding from her backside. They mated during the spring following their arrival and produced a brood of 10 peachicks, which we put in a wading pool for safe keeping.

Alas, the peachicks all drowned in a summer rainstorm, while Priscilla was eaten by a fox a year later. Percy, who unlike Priscilla, who was a broody type as befits a female bird, would take to the higher branches of trees when evening fell, a black walnut in warm weather and an arborvitae in the winter. He lived to the ripe old age of 21.

* * * * *
All this by a long-winded way of saying that the story of how Percy and other peacocks got their eye spots has taken a new turn.

It has long been understood that the peacock's train of feathers are terrific, if loud, examples of what Darwin called sexual selection. In this case, Percy had a better chance of getting laid because of his flashy plumage.

This basic principle is not in doubt, yet "everybody uses it without knowing much about how it works," says Roslyn Dakin of Queen’s University in Kingston, Canada.

Watching how peafowl courtship played out in three clusters of free-roaming birds, Dakin found that shimmying a train with especially high numbers of eyespots did not seem to improve a male's chances of dazzling a female into mating.

Eye spots seemed a good predictor of a male’s chances of success in past studies of peafowl in England. A female cruising among males routinely picked the one who showed her the most eye spots, says a pioneer of peacock science, Marion Petrie of the University of Newcastle in England. Among her other eye spot studies, snipping 20 feather tips out of males’ trains ruined courtship success. Fastening the eye spots back into the train put the males back in the game.

Feathers were ruffled in 2008, however, when Japanese researchers studying feral peacocks reported finding no courtship advantage for eye spot number. Such displays may have become "obsolete" as a signal to peahens, the team proposed.

Dakin and colleague Robert Montgomerie have now found similar results in two peafowl populations in Canada and one in the United States. Dakin repeated part of Petrie’s eye spot-snipping experiment. As predicted, males deprived of 20 of their eye spots -- leaving fewer than 138 in the displays -- managed to mate fewer times overall than fully eye spotted males.

When Dakin and Montgomerie pooled their eye spot data with other published reports, eye spot effects didn't show up among the top 75 percent most successful maters of 102 peacocks. Yet the most eye spot-challenged birds, flashing numbers only in the 120s and 130s, rarely had any mating success at all.

"It certainly looks like a threshold," Dakin says, although she doesn’t have data on whether individual peahens have a response threshold.

Percy unavailable for comment.


Anonymous said...

We have peacocks that live in the woods around us, they were escaped and abandoned pets. I often see one of them up in the tallest of fir trees, 75 to 100 feet off the ground. It is the season of love here presently...sounds rather like somebody is being murdered in the woods several times a day!

Shaun Mullen said...

I became used to and eventually very fond of Percy's repertoire of screeches, trills, honks and a foghorn sound so realistic that you expected to see an ocean liner coming up the driveway.

His winter roost was high atop an arborvitae right outside my third-floor bedroom. He was great company and I don't thing I ever met a creature who used to much of his brain. He was street smart in a way to our others birds -- guinea fowl, geese, ducks and chickens -- were most definitely not.