Thu, Dec 06, 2018 - Page 6 News List

Polyamory a new threat to endangered swift parrot

The Guardian

Tasmania’s critically endangered swift parrots are facing a new threat to survival: polyamory.

A study by researchers at the Australian National University, published in the Journal of Animal Ecology, has found that a chronic shortage of female swift parrots caused by intensive predation by sugar gliders has wreaked havoc on the bird’s usually monogamous breeding habits and lowered the survival rate for young hatchlings.

Lead researcher Rob Heinsohn said that the unusual behavior was caused by a significant disparity in the number of males and females in the parrots’ breeding grounds of the blue gum forests in southeast Tasmania.

Surplus bachelor males were pressuring paired-up females for sex and getting into fights with paired males.

Predation by sugar gliders, which were introduced to Tasmania from mainland Australia in the 1800s, had changed the gender ratio in the swift parrot population from about an equal number of male and female birds to three males to every female, Heinsohn said.

Females are at more risk from sugar gliders, because the marsupials attack their tree-hollow nests while the females are incubating their eggs.

The gender imbalance was “really causing havoc with their love lives and their usual mating system,” Heinsohn said.

“Usually they would be quite conservative, boring even, with their mating habits. They are just monogamous pairings,” he said. “At the moment, there are all these bachelor males. They turn up at the nests of the breeding pairs and they harass the females endlessly.”

“They are just pressuring them constantly for sex, basically, and just making a real nuisance of themselves,” he added.

The females usually give in “but they do it sneakily behind the resident male’s back,” Heinsohn said, adding that breeding males spend their time fighting off bachelors.

Researchers took blood samples from hatchlings to conduct a DNA analysis and found that more than half the nests had more than one father.

Heinsohn said the pressure from bachelor males distracted the breeding pair from feeding, which reduced survival rates.

The number of eggs being produced has not fallen, but fewer were making it out of the nest.

“They are spending so much of their time, the male in defending the female and the female avoiding being harassed, that it’s affecting their ability to get food,” he said.

Swift parrot numbers have declined significantly in the past four years. It is estimated that only 1,000 breeding pairs remain.

Australian National University researcher Dejan Stojanovic, who coauthored the paper, said he had been hopeful of a more successful breeding season this year, because most of the wild population settled on Bruny Island, which is free of sugar gliders.

However, three weeks of rain washed most of the nectar out of the native flowers, meaning that a lot of the hatchlings have died from lack of food, Stojanovic added.

Conservationists have introduced measures to control sugar gliders, like installing light-sensitive nesting boxes that close off at night, locking out the nocturnal gliders, and working with the Tasmanian Government on possible methods of reducing glider numbers.

However, Stojanovic said that the underlying issue of habitat loss had not been addressed.

Logging of blue gum forests in southern Tasmania has reduced the appropriate breeding habitat by one-third over the past 20 years and conservationists have warned that a decision in August to extend a regional forest agreement to allow that logging for another 20 years effectively condemned the species.

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