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Playing favourites: Coot bird preference for colourful chicks helps larger broods survive
American coot birds are known to play favourites with their young, showing preference to chicks who are more brightly coloured. But new research suggests that may be a reproductive behaviour designed to help larger broods survive. (University of California)
TORONTO -- Parents aren’t supposed to play favourites with their children, but that logic may not hold true in the animal kingdom.
The American coot, commonly found in North American wetlands, is an unassuming water bird with gray and black feathers. But their chicks have long fascinated researchers thanks to their outrageously bright orange and red feathers and beaks.
Previous research has shown that coot parents preferentially fed their brightest offspring over those whose feathers were more muted, giving the “prettier” chicks a better chance at survival.
But new Canadian research suggests this game of favourites may be a reproductive behaviour designed to help larger broods survive.
Researchers with the University of California, who have been conducting field research on the birds in B.C., now believe the colouring of coot chicks is associated with hatching order.
The later a chick hatches, the more colourful it is. But these birds are the runts of the litter.
According to researchers, coot birds don’t show any parental preference during the first 10 days after the chicks hatch – they simply feed whichever chick reaches them first when they return to the nest with food.
The first chicks to hatch, though more muted in colour, get a head start on growth which means they get fed first.
But research shows that changes about 10 days after the last chick hatches. The birds then start to show favouritism towards the later-hatched, more colourful chicks, allowing them to catch up in size and strength to their siblings.
"The male and female divide up the brood, with each parent exclusively feeding their half of the brood, and each parent also picks a favourite,” study author Bruce Lyon, professor of ecology and evolutionary biology at the University of California Santa Cruz, said in a press release.
“Colour predicts which one they choose, so the ornamentation may serve as a signal to tell them which chick needs the most help.”
Lyon says this unusual tactic is likely thanks to the coot’s “harsh” reproductive pattern, which see the birds laying lots of relatively small eggs, often producing more chicks than the food supply can support.
"It's very efficient for coots, because their eggs are not very costly to produce. By laying an optimistic clutch size and then culling the brood to bring it in line with the food supply, they're always raising as many chicks as they can," Lyon said.