Look like a punk and live longer: When American coot chicks don King's Road plumage, it's not to rebel against their parents but to survive. Mark Pagels explains
Tuesday 18 October 1994
Adult American coots are sooty black birds somewhat smaller than a duck, and, like similar British coots, inhabit streams and lake shores. Coot chicks, however, emerge from their shells with bright orange plumes around their necks and shoulders that stand out sharply against their darker natal down. These plumes make the chicks more conspicuous to predators and so represent a risky choice of attire for an already vulnerable creature.
Recently, a team of Canadian researchers, reporting in the science journal Nature, uncovered the reason for this risky choice of plumage. The chicks' lives depend upon it: American coot parents have favourites among their chicks and feed them more. These favourites are those chicks that produce the bright orange plumage.
Why do coot parents have such eccentric tastes? One possibility that will seem all too familiar to human parents is that it is the parents that must put up with the chicks' tastes, not the other way around. Coot chicks gradually lose their orange plumage as they progress towards fledging, which occurs at about three weeks. Feeding a chick more may hasten the day it fledges and thereby reduce the risk of its being preyed upon.
The chicks may be employing their bright plumage as a form of blackmail, to get their parents to feed them. Their strategy mimics that of the child who holds its breath to get its parents' attention. The difference, of course, is that holding one's breath is generally self-correcting (but try telling a parent), while playing with one's life to blackmail parents may not be: the first chick to attempt this was likely whisked off by a predator. Blackmail as a strategy, if it ever evolved, probably quickly died out.
A more plausible reason is that American coots, like many bird species, practise bet-hedging: they lay more eggs than they normally can bring up. In a bountiful year, the payoff to laying a large clutch of eggs is high: the parents produce many young, thereby banking lots of Darwinian currency. But because eggs themselves are not so costly for parents to produce, losing a few in bad years is, in theory, more than compensated by the occasional good year. Thus, to keep up with their neighbours in the reproductive stakes, coots are forced regularly to confront something of an avian Sophie's Choice.
This in turn has profound implications for the chicks. Six is a common clutch size, but the chosen few may number only two or three. At the expense of their siblings, chicks must actively convince their parents that they should not be among the dispossessed. Thus life for young coots unfolds in a ruthlessly Hobbesian state of Nature, in which brother and sister fight each other to inherit the rights to the next generation.
Bright orange ruffs are the strategy that the coot chicks have hit upon to secure that inheritance. If these plumes are costly for chicks to produce - because they divert energy that might otherwise have gone into growth, or because they increase the risk of being preyed upon - and only the healthiest chicks can produce them, then the plumes may be a reliable indicator of a chick's worth. Indeed, by choosing something so frivolous and risky, the chick is effectively saying to its parents that it is of such high calibre that it can afford to handicap itself. The worth or quality that it is advertising may be some aspect of its health or condition, or that it has good genes, or both.
In a different setting, but illustrating the same principle, individuals of some bird species sing when being chased by a predator. Their songs are not designed to warn others of the approach of the predator, but to show their assailant that they are so fit they can afford to waste precious breath while being chased for their life. (Such signals are kept honest by their consequences.) Being a coot chick is akin to living in a welfare state with a form of inverted means-testing: the most fit, and therefore the least needy, receive the most aid, while the runts are overlooked.
If the coots' formula for parental attention offends your sensibilities, you will find little comfort by retreating to the special place in nature that humans are meant to occupy. Anthropologists report that some human groups regularly exercise choice among offspring, routinely favouring the strongest over the weakest. Among human groups, neglect of less-fit children can extend from simple favouritism to abandonment, to fostering out, and even to infanticide. In some groups, handicapped offspring were once (and may still be) abandoned, and in a practice redolent of bet-hedging, a Khoisan- speaking hunter-gatherer group routinely practises infanticide on one of a pair of twins.
Still, human offspring, by dint of arriving typically in small 'clutches' of one, avoid much of the 'nature red in tooth and claw' that might otherwise be directed their way. Having one child at a time, and having so few compared to other animals, means that we tend to invest heavily, if not always equally, in each. This may be why, apart from the occasional adolescent or even adult deviation along the King's Road, the nascent human tends not to appear with spikey orange hair.
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