Lights From Beachfront Development Harm Endangered Beach Mice

“We already know that light pollution can have an adverse impact on sea turtles and coastal birds,” said Lyn Branch, a professor of conservation biology at UF’s Institute of Food and Agricultural Sciences. “Now we’re finding that it can also have an effect on coastal mammals.”

Branch and her fellow researchers found that artificial lighting interferes with the foraging behavior of the Santa Rosa beach mouse, one of seven mouse subspecies that live in dunes along the Florida and Alabama coasts. The results of their study appeared in the October issue of the journal Conservation Biology.

Closely related to the common field mouse, the various subspecies of beach mouse sport light-colored coats that help them blend in with sand, live in burrows in the dunes, and come out at night to feed on sea oat seeds and insects.

In recent decades, the mice have been threatened by both development and the forces of nature. The mice typically are found in primary dunes -- the high-standing dunes closest to the water’s edge -- and in shrub-covered “scrub dunes” found on the bay side of many barrier islands. Primary dunes often are destroyed when hurricanes make landfall, while many scrub dune areas have been destroyed by development.

One beach mouse subspecies, the Pallid beach mouse, already has become extinct. Of the remaining seven, only the Santa Rosa beach mouse -- found on Eglin Air Force Base and Gulf Island National Seashore -- is not listed as endangered or threatened. Because of its similarity to other subspecies, and because of the difficulties of conducting research with protected species, researchers often use the Santa Rosa beach mouse as a stand-in for its endangered cousins.

Like other nocturnal mammals, the Santa Rosa mouse doesn’t spend much time foraging when the moon is full.

“Increased lighting makes the mice more visible, and that can only increase their vulnerability to predators,” said Brittany Bird, the former UF graduate student who set up the study. “Beach mice are particularly vulnerable to predation by domestic cats, because they evolved in a cat-free environment and haven’t evolved ways to recognize and avoid them.”

The UF researchers wanted to find out if artificial lighting might have the same effect. They put up two sets of artificial lights -- 18-watt low-pressure sodium lights and 40-watt incandescent bug lights -- at four locations on an undeveloped area of Santa Rosa Island managed by Eglin Air Force Base. They set up trays filled with food at locations around each set of lights, and placed similar arrays along darkened stretches of beach.

After observing each site during a new moon, the researchers found that mice were less likely to eat from trays in lighted areas, indicating that light may discourage foraging. The effect was strongest near the bug light, where mice ate one-third as much as they ate in darkened areas, but the researchers also saw a decrease in foraging near the sodium bulb.

The researchers say the study may underestimate the effect light has on mice in developed areas. They note that the lights in the study were placed near the ground, on otherwise darkened stretches of beach, with lots of vegetation where mice can hide. Many beachfront buildings have multiple outside lights, and vegetation is typically sparse on dunes in developed areas.

“There’s more than just one house on the beach, and there’s usually more than one light per house,” Branch said. “And there are large portions of beach that are lit by taller, brighter lights than the ones used in the study.”

Reduced foraging could hamper the recovery of the endangered mice, the researchers say.

“If they have fewer resources, that could reduce their reproductive rate, which would make it tougher for endangered subspecies to increase their numbers,” said Debbie Miller, a UF associate professor of ecology and wildlife conservation and co-author of the study.

Even the glare from off-beach sources can be bright enough to cause problems for wildlife, said Lorna Patrick, a biologist with the U.S. Fish and Wildlife Service’s Panama City field office, which partially funded the study.

“The urban glow from areas far behind the dunes can cast a lot of light on the beach,” Patrick said. “We’ve seen light ordinances put in place in quite a few coastal communities in recent years, but with continuous coastal development, the amount of light in these areas is still growing.”

Patrick said coastal residents concerned about threats to beach mice should try to limit the amount of light they allow to escape their property.

“People often want bright lights because they believe they will make them safer in the urban environments,” she said. “For a long time, the philosophy was ‘the brighter, the better.’ But putting the right light in the right place can work just as well.”