Light pollution delays wallaby reproduction and puts joeys at risk
Artificial light is causing some wallabies to delay when they give birth, putting them out of sync with the food resources they need to feed their young, new research suggests.
And energy-efficient LED lighting could make matters worse, unless care is taken to develop “wildlife-friendly lighting”, say the authors in today’s Royal Society journal Proceedings B.
“These results suggest that urban light pollution could have profound impacts on desynchronising seasonal physiological processes in wildlife,” the researchers wrote.
Artificial light is increasing at 6 per cent per year globally and there is concern it could affect the timing of reproduction of animals whose breeding season is cued by changes in day length.
To investigate this phenomenon, zoologist Dr Kylie Robert of La Trobe University in Melbourne and colleagues studied tammar wallabies (Macropus eugenii), which time their breeding like clockwork to fit in with the seasons.
In the natural environment most tammar wallabies give birth around six weeks after the summer solstice, carrying the joey for 300 days in the pouch.
This timing ensures the growing joey reaches its peak milk demand the following spring when food is abundant.
Tammar wallabies are believed to use the gradual shortening of day lengths to detect when the summer solstice has passed and when they should give birth.
But this makes them a prime candidate for their reproductive cycles to be affected by artificial light.
Bush wallabies vs naval base wallabies
For their study, Dr Robert and her colleagues looked at two populations of wallabies on Garden Island off Western Australia.
Those in the north of the island live in native bushland, fenced off from those on the south of the island, which are exposed to lights from Australia’s largest naval base, HMAS Sterling.
“The naval base is lit up like a Christmas tree,” said Dr Robert.
The researchers took note of when the wallabies on both sites gave birth and used special GPS collars with light loggers to record how much light the animals were exposed to.
“We found that those on the naval base had massive levels of light, while those on the bushland site had only natural levels of light,” Dr Robert said.
Finally, the researchers took blood samples and measured night time levels of the hormone melatonin, which rises in the dark and helps regulate the animal’s body clock.
“We found those on the naval base had suppressed melatonin levels at night.”
After five years of observations the researchers saw wallabies on the naval base were giving birth later.
“We noticed that the median birth date of wallabies on the naval base was a month later than those at the bushland site,” said Dr Robert.
The findings support the idea that light pollution on the naval base is suppressing melatonin and “masking” the cue that wallabies would normally get from shortening day lengths.
Picture: Tammar wallabies spend 300 days in the pouch. Supplied by Kylie Robert
Out of sync with food supplies
The delay in the birth date could potentially have an impact on survival of the offspring if the mothers miss the peak in food resources when they most need it, said Dr Robert.
Although Dr Robert and her colleagues did not initially observe any effects on offspring, she said this was likely due to a complication in the study.
Irrigated lawns at the naval base provided a food source for the wallabies all year round and “buffered” the base animals from missing the peak in natural food resources, she said
But, said Dr Robert, since the study was completed irrigation had ceased due to water restrictions and preliminary observations suggested this had had an impact on wallaby offspring.
“Mothers are abandoning their offspring when things get too hard,” Dr Robert said.
The findings could also apply to Bennett’s wallaby, and other animals such as bandicoots, antechinus, dunnarts and even Tasmanian devils.
Dr Robert said this problem could be compounded by a big push towards energy-efficient LED lighting.
“LED lights produce a wavelength of light that is in the blue spectrum, which has a higher negative impact on melatonin suppression,” said Dr Robert, who is currently involved with an industry partner, developing “wildlife-friendly lights”.
“We’re now looking at producing LED lights that don’t produce that wavelength,” she said.”Posted: September 30, 2015