Parrot kills male babies to save females

By Natalie Muller 27 October 2011
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Mother Eclectus parrots peck their male babies to death to save the females who are easier to raise.

A TROPICAL PARROT IS the only known species in the animal kingdom – besides humans – to kill its offspring because of its gender, Australian researchers have discovered.
The Eclectus parrot, native to tropical Australia and Papua New Guinea, will sometimes kill its male chicks, pecking them to death soon after they hatch. With the males out of the picture, faster-growing female chicks have a much better chance of surviving adverse conditions.

A team of researchers from the Australian National University in Canberra has spent the past 10 years studying the behaviour of Eclectus roratus parrots in the tropical rainforests of Cape York in Queensland.

“There has to be precise circumstances in which the female parrot would commit infanticide,” says Professor Robert Heinsohn, lead author and evolutionary biologist at ANU. “Humans are the only other species that systematically kill their own offspring of one sex. But here’s a case in Eclectus parrots where we can show there is a very clear adaptive reason.”

Their research was published this week in the journal Current Biology.

Female parrots easier to raise

The parrots build their nests in tree trunk hollows about 30m above the ground, but there aren’t always enough homes to go around. In fact, there are so few of these havens that females will literally fight to the death to secure one to breed in.

Those birds that end up in low, flood-prone hollows will have a much tougher time raising their young, especially during torrential rains.

“The hollow could fill up with water at any time and they only have these very small windows of time to operate in,” Robert says. “And if they have a male chick in the nest, that slows down the whole process.”

Female chicks fledge up to seven days earlier than their male siblings, so mothers in poor nest hollows have a better chance of success if they kill the male chicks and concentrate their maternal efforts on the female.

Dr Glen Chilton, ornithologist at James Cook University in Townsville says while infanticide is rare, it’s not uncommon for species to produce more offspring than they can raise.

“The female American white pelican always lays two eggs and never raises more than one offspring; they just cannot do it, and so that second egg is insurance,” he says. “Eclectus parrots are doing their best to make a genetic contribution to following generations. They’re driven to do it. It’s built into their genes.”

A male (green) Eclectus parrot feeds a female (red). (Credit: M. Cermak)

Parrots can control the gender of a baby

The parrots also have the incredibly rare ability to be able to control the sex of their offspring. Often, but not always, they can produce a string of females or males in a row.

Mother Eclectus parrots living in flood-prone nests seem to have evolved the ability to produce fewer males than the females living in safe hollows – meaning they don’t have to kill as many babies.

Robert says infanticide is already skewing the sex ratio of the birds.

“That means those females will have trouble finding mates,” he says. “However, provided [they] don’t do it too often, the benefits of producing at least one surviving chick are such that you can get away with it.”

Climate change affects

Climate change and the weather are also likely to impact the viability of parrot nests in the future, especially if there are extended wet seasons. “That would mean a lot more flooding of these hollows, which will have a dampening effect both in terms of numbers and in terms of the skewed sex ratio,” says Robert.

But Glen is optimistic the Eclectus parrot populations will be fine because he says there are other mechanisms in place to balance the sex ratio. For example, if the wet season brings more females, perhaps the dry season will be favourable for male chicks. Or if more females are born in poor nests, perhaps more males are born in the good nests. Future research will focus on these questions.