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Moonlight No Delight for Ocelots


We get it on most every night
when that moon gets big and bright
it's a supernatural delight
everybody's dancin' in the moonlight.
—Sherman Kelly, "Dancin' in the Moonlight"


I see the bad moon arising.
I see trouble on the way.
—J.C. Fogerty, "Bad Moon Rising"

 

To most of us, the idea of dancing in the light of a full moon is a romantic delight. For ocelots, a full moon is more like "the bad moon arising."

ocelot
An ocelot on the hunt.

That was the tentative conclusion of a study by Louise Emmons, research associate at the Smithsonian's Museum of Natural History, and her colleagues, published in 1989 in the book Advances in Neotropical Ecology, in a paper entitled "Ocelot Behavior in Moonlight." These biologists were studying ocelots (Leopardus paradalis) in Peruvian tropical rainforest. Ocelots are primarily nocturnal hunters but may be active day or night; as many cats do, they walk along trails and visit beaches while hunting their rodent prey. On trails and beaches, ocelots can walk more quietly and easily and see prey from farther away than if they were plowing through vegetation. But they do not use trails or visit beaches during the day, even when they are active, sticking to the cover of vegetation.

Emmons also found that ocelots generally avoid trails and beaches on nights with full moons, even though they are active just as many hours and walk just as far as they do on darker nights. It appears that the predators keep off brightly moonlit trails and stick to traveling under the darker cover of vegetation to look for a meal. In turn, their primary prey, nocturnal spiny rats (Proechimys spp.), follow a similar pattern: They are more often seen on trails on dark nights than on bright nights, although they are equally active under both conditions.

Other evidence suggests, however, that ocelots are no more, and probably less, successful hunters when confined to vegetation, which likely hampers their ability to see prey, sneak up on it undetected, and pounce on it amid the undergrowth. Spiny mice and other small rodents, in contrast, probably avoid moonlit trails to decrease their risk of predation by birds of prey, which may be better able to see small animals when the night is bright. This forces the ocelots into the bush to find something to eat. It is also possible that avoiding trails and beaches during the day and full moons reduces the chances of ocelots themselves becoming the prey of jaguars (Panthera onca), pumas (Puma concolor), or harpy eagles (Harpia harpyja).

Other things being equal, a few days a month of eating a few less spiny mice is probably not a huge hardship for ocelots. But what if artificial night light forces them to stay under the cover of vegetation all the time? Or worse, what if there is no vegetation at all?

A small, endangered population of ocelots is clinging to survival in south Texas, in two refuges near or bordering the Rio Grande, which forms the international boundary between the U.S. and Mexico. These refuges do not form a large contiguous protected area; rather, protected tracts are linked by unprotected corridors that often lack vegetation. This probably makes it difficult for ocelots to move between the protected tracts. Making matters worse, to combat illegal immigration across the Rio Grande, the U.S. Immigration and Naturalization Service's Border Patrol burns and mows vegetation along the border and has installed miles of lights that brightly illuminate the border at night.

This concerns Melissa Grigione, a professor in the University of South Florida's Department of Environmental Science and Policy and cofounder of the Border Cats Working Group, which also focuses on the conservation of jaguars and jaguarundis (Puma yagouaroundi), which too are barely hanging on along the U.S.-Mexico border.

In a 2004 paper published in the journal Urban Ecosystems called "Effects of Artificial Night Lighting on Endangered Ocelots and Nocturnal Prey Along the United States-Mexico Border," Grigione and her colleague Robert Myrkalo reviewed existing studies, including Emmons', to assess what might happen to the Texas ocelots. They suggest that loss of vegetation in which ocelots can find cover while hunting or traveling between protected areas, and nocturnal artificial illumination that may alter the activity or abundance of rodents and reduce ocelot foraging success, may be serious threats to the recovery of these ocelots. Further, both night light and little cover may prevent them from moving across the Rio Grande to join populations in Mexico, and vice versa.

While experiments to test these ideas have not yet been conducted, Grigione says the prudent thing would be to eliminate artificial lighting or increase vegetation so ocelots and their prey have sufficient cover to shield them from artificial lights. Thus far, however, neither action is being taken.

—Susan Lumpkin


ZooGoer 36(1) 2007. Copyright 2006 Friends of the National Zoo. All rights reserved.

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