The last few years have seen a push for more energetically efficient light sources, such as white LEDs. But energy saving lights' lower carbon footprint comes at a cost: light pollution. Artificial night lights are a rapidly growing form of man-made pollution, and the bright white lights of LEDs can obscure signals that wild animals rely on for everything from foraging behavior to communication to re-production. A new study published today in Proceedings of the Royal Society B has found that night lights can interfere with the carefully timed re-productive cycle of Australia's tammar wallaby.

Scientists have been studying the re-productive behavior of the rabbit-sized, nocturnal marsupial for at least 180 years. In that time, the timing of wallaby births has remained almost unchanged. Among a population of tammar wallabies on Garden Island—a landmass five miles off the coast of Western Australia—the median birthdate shifted by only five days between 1830 and 1977.

In the current study, researchers from Australia and Germany looked at two small populations of wallabies on Garden Island: one that lives on the southern end of the island, where the country's largest naval base produces a significant amount of light pollution; and a natural bush population undisturbed by manmade lights at the northern tip of the island. The researchers found that the wallaby population near the naval base experienced a good deal more night-time light intensity than their cousins in the bush, which appeared to suppress melatonin secretion—a critical hormone for tammar wallaby re-production. As a result, the median birth date for base-living wallabies was a full month later than those living in the bush.

Such changes in re-productive timing can have dire consequences for offspring, when birth times no longer line up with peak vegetation resources. Until recently, irrigated lawns were a major forage source for base-bound wallabies, which the researchers believe buffered the population of the negative effects of late birth times. But future generations will not be so lucky: The Australian Department of Defense has built a fence around the only irrigated grasses on the base to keep out the wallabies.