Alien plants may pose risk for flying foxes

Introduced ‘alien’ plant species aren’t providing a balanced meal to Christmas Island flying foxes (Pteropus natalis), scientists say, with implications for colonies across the country.

Just 3800 flying foxes – also known as fruit bats – are left on Christmas Island. One of their biggest threats is the changing natural habitat, with humans planting many non-native species like mango, banana, breadfruit and Japanese cherry trees.

But these alien species may not meet the nutritional needs of these critically endangered bats, according to paper published in the journal PLOS ONE.

The research team analysed 125 native and non-native plant samples that the flying foxes commonly feed on, and found that non-natives contained more carbs but had lower mineral concentrations.

This means that eating the fruit and nectar of non-natives – some of which fruit year-round when other food is scarce – might make it easier for flying foxes to quickly meet their energy requirements, but not the rest of their nutritional needs.

The best diet would encompass a variety of native foods, according to lead author, University of Sydney PhD candidate Laura Pulscher.

“Our findings suggest that preserving these animals’ complex foraging habitats is key to their conservation,” she says.

A recently captured Christmas Island flying fox. Credit: Leonie Valentine.

According to Phil Cassey, an ecologist from the University of Adelaide who was not involved in the study, this is important research.

“With the increase in anthropogenic habitats being characterised by alien and invasive species, the impacts on behaviour, diet and welfare of native species are often poorly studied, or recognised,” he says.

He points out that on mainland Australia, flying foxes are changing their distributions – like the Grey-headed flying fox, which has moved into South Australia in response to food shortages on the east coast.

“It may be that their dietary and ‘health’ needs are being insufficiently met by an abundance of exotic/alien fruiting and flowering trees,” Cassey says.

But before we extrapolate this research to mainland species, we need to be sure of the link, says Wayne Boardman, a wildlife veterinarian also from the University of Adelaide who works with Adelaide’s urban flying fox population.

“Are they actually eating some of these plants? We don’t know,” says Boardman, who suggests analysing the Christmas Island populations’ feces to determine how non-native plants contribute to their diet.

Examining abnormalities in body condition and breeding can also help determine if eating non-natives is contributing to population decline.

Boardman points out that the 25,000-strong Adelaide colony primarily eat non-endemic species, which may be part of the reason they are “in better condition in winter than in summer, which is opposite to what we see in the eastern states”.

If mainland populations can’t find food, they can migrate – but on Christmas Island, 2500 kilometres off the West Australian coast, the isolated population is reliant on the food at hand.

“Clearly the diversity of food plants and parts required to sustain flying fox populations is complex, and this will impact how restoration and conservation wilding activities are focused in the future,” Cassey concludes.

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