If you own a cat, he probably bugs you in the kitchen, hoping to score some scraps from the meal you're making. But in the wild, your cat's cousin, the puma, supplies the leftovers. A new study reveals that carcasses abandoned by these big felines provide surprisingly large amounts of meat to a diverse group of scavengers, including the rare Andean condor (Vultur gryphus).
"I believe this is the first study to document that a large, solitary carnivore provides a significant food subsidy for scavengers, other carnivores, and omnivores," says Paul Beier, a wildlife ecologist at Northern Arizona University in Flagstaff who wasn't involved in the research. "This adds to the increasing evidence that top predators have important effects on communities and ecosystems."
Pumas aren't the largest cats in the Americas, but they're the widest-ranging. Puma concolor, commonly known as puma, panther, mountain lion, cougar, and dozens of other names, is found in every major type of habitat, from southeastern Alaska almost to the southern tip of South America. Despite their extensive range, researchers know little about the behavior of these solitary creatures, says Mark Elbroch, a wildlife ecologist at the University of California, Davis. Now, a first-of-its-kind field study by Elbroch and Davis colleague Heiko Wittmer has shed new light on the puma's ecological role. Between March 2008 and September 2009, the researchers caught nine pumas living in a 1100-square-kilometer region in southern Chile and strapped GPS-equipped radio collars on them. As the creatures roamed their home ranges, the collars recorded their location every 2 hours and relayed that info to the scientists once every 2 to 5 days. If the cats spent more than 2 hours in one spot around dusk or dawn or during the night, the researchers went to that site to check for the remains of puma prey.
Between March 2008 and December 2010, the scientists located 433 puma-killed carcasses. By estimating the prey's weight and how much the pumas (and any kittens they had) ate, Elbroch and Wittmer could calculate how much meat the cats left behind—either when they got full and moved on or were scared away from the carcass by groups of scavengers. Then, they used that data to estimate how much meat was abandoned by the entire puma population in the region.
Altogether, pumas in the study area—a region about six times the size of the District of Columbia—abandoned more than 2.5 metric tons of meat each month, the researchers report online today in Biology Letters. Visits to the carcasses reveal that the cats' leftovers are an important source of food for numerous species of scavengers, including the rare Andean condor, which was found at almost 30% of the kill sites. The researchers also recorded eight other species of carrion-eating birds, two mammals, and even a lizard taking advantage of the remains—although the tiny reptile was probably feeding on insects attracted to the carcass, says Elbroch.
"Nobody has looked at this with pumas before," says Christopher Wilmers, a wildlife ecologist at the University of California, Santa Cruz, who was not involved in the study. Besides enhancing the biodiversity of the ecosystem, the scavengers supported by puma provisions are available to quickly consume the carcasses of creatures that died due to natural causes, thereby removing possible sources of disease, he suggests.
Your dog's ancestor isn't so generous with its leftovers. A 3-year field study in Yellowstone National Park, published in 2003, revealed that wolves there each month abandon between 85 and 156 kilograms of meat for every 100 square kilometers of their range, or between one-third and two-thirds the average amount left by pumas. That difference probably stems from the disparate hunting strategies of pumas and wolves, says Elbroch. Whereas pumas are solitary hunters and are easily scared away from their kill, wolves hunt in packs and therefore have more opportunity to finish their meals.
Besides providing meat for their ecological neighbors, wolves in Yellowstone are credited with bringing back aspen to sites where elk, which typically browse saplings down to ground level, now feel vulnerable, says Elbroch. That, in turn, has allowed shrubs and other vegetation to thrive as well, changing the habitat and making it more attractive to songbirds and a variety of other creatures. Puma predation may have similar positive effects in some landscapes, although in other ecosystems the influence of the big cats' presence may be more subtle, Elbroch notes.
Pumas are increasingly threatened, largely due to habitat loss and indiscriminate killing by farmers and ranchers. Besides possibly leading to a substantial decline in scavengers that may depend on puma leftovers, one of the largest effects of losing pumas would likely be boom-and-bust population cycles in prey animals such as deer. For example, deer proliferation after the disappearance of puma could lead to overgrazing of vegetation that, in turn, could trigger a mass starvation of deer.