Vertebrate Diversity Benefiting from Carrion Provided by Pumas and Other Subordinate, Apex Felids

1. What they did

Animals that eat carrion move energy and nutrients through food webs and help keep ecosystems stable. Large carcasses feed the most kinds of scavengers, and large predators provide them all year round. Felids that are top predators but give way to other carnivores in competition, such as cheetahs and pumas, are thought to leave more carrion for others than other top predators do. As stalk-and-ambush hunters they spend less energy catching prey than chasing predators like wolves, so losing part of a kill costs them less. Pumas lose or abandon on average 39% of their prey to competitors and scavengers.

The researchers asked how many kinds of vertebrates benefit from puma kills in the Greater Yellowstone Ecosystem, north of Jackson, Wyoming:

• Capturing pumas. In the winters of 2012 to 2015 they used trailing hounds to tree pumas, then fitted them with Global Positioning System (GPS) collars that took a location every two hours.
• Finding kills. They searched clusters of GPS locations (two or more locations, at least 4 hours apart in total, within 150 m) for prey remains. From the state of the remains, bite marks, bleeding at wounds and the parts eaten, they judged whether the puma had killed the animal or was scavenging.
• Filming scavengers. Where enough meat remained (for example, the carcass was cached, or meat still covered the leg bones), they set paired motion-triggered video cameras. Only animals that clearly fed from the carcass were counted (for small songbirds, possibly eating insects on it).
• Comparing and modelling. They compared the scavengers with the local lists of mammals (60 species) and regularly seen birds (201 species). They tested whether scavenger diversity at each carcass depended on temperature, canopy cover, carcass weight or how long the camera ran.
• Looking worldwide. They identified other felids like the puma and mapped their combined range.

2. What they found

Kills and cameras

• They collared 15 pumas (5 males and 10 females), found 1022 kills, and filmed 242 kills of prey averaging 135 kg.
• Cameras went up on average 43 hours after the kill and ran for 7 days on average.

Who came to eat

• 39 species of birds and mammals scavenged at puma kills, the highest number of vertebrate scavenger species of any study so far. Domestic dogs were also recorded but not counted.
• Red foxes and black-billed magpies came to by far the most kills (151 and 149), followed by golden eagles (73), common ravens (59) and coyotes (54). Pumas were recorded at 44 kills.
• Scavengers made up 28.3% of local mammals (17 of 60), 10.9% of local birds (22 of 201) and 14.9% of all local birds and mammals.
• This was more species, and a higher share of local birds and mammals, than nine studies of scavengers at hunters’ leftovers worldwide, and more than three times the species recorded at wolf kills and hunter kills just north of the study area (the authors note that different methods may explain part of this).

What affected diversity

• Diversity at a carcass (mean Shannon’s H 0.83) was fairly steady across temperatures, carcass sizes and canopy cover.
• The two best models included how long the carcass was filmed, plus either carcass weight or temperature. Neither explained much: 10% and 9% of the variation. Filming time had the clearest effect; weight and temperature had very small ones. Canopy cover had no support.
• Some scavengers were seen only in warm weather (for example grizzly bears and chipmunks), while others, such as red foxes, magpies, golden eagles and ravens, came across the full range of temperatures.

Puma-like felids worldwide

• Six other felids fit the pattern (stalk-and-ambush hunters over 20 kg that kill prey larger than themselves and give way to other predators): cheetah, leopard, Eurasian lynx, snow leopard, clouded leopard and Sunda clouded leopard.
• Together with the puma, their ranges cover about 58 million km², or 43% of land outside Antarctica. The snow leopard is endangered and four of the others are vulnerable. Cheetahs live in only 9% of their historic range and leopards in 25 to 37%.

3. What they concluded

• Pumas, and possibly other felids like them, play an important role in producing carrion that feeds a wide range of birds and mammals, and they contribute to ecological stability through predation and their tolerance of scavengers at their kills.
• Filming time mattered most, so future studies need longer sampling at carcasses and research on how long it takes to record the full range of scavengers.
• Their sampling favoured large carcasses, which lasted long enough to set cameras, so the effect of carcass size was not properly tested. A next step is to check whether different species come in different seasons or habitats, even when the number of species stays similar.
• The wide ranges of the seven felids, even after centuries of persecution, show how adaptable they are and may point to their importance in many ecosystems.

4. How tracking was or was not used

• Finding animals for capture: pumas were caught with trailing hounds, which forced them up a tree. Who handled the hounds is not reported.
• Reading kill sites: at GPS clusters, field teams searched for prey remains and used signs at the carcass (the state of the remains, the presence and position of bite marks, bleeding at wound sites, and which body parts were eaten) to decide whether the puma had made the kill or was scavenging. A cached carcass, or enough meat left on the leg bones, was taken as a sign that the puma would return and that scavengers would come, and decided where cameras were set.

5. Tracker or observer certification

Not reported. The paper does not say who interpreted kill sites or how their skill was checked, although the choice of which kills to film rests on that sign interpretation. P. Lendrum, A. Kusler, J. Williams, N. Wight, C. MacFarland, B. Smith and S. Smith are thanked for fieldwork.

6. Other technologies, skills or innovations

• GPS collars (Lotek Globalstar S or Iridium M; Vectronics Globalstar GPS Plus) sending locations by satellite six times a day or once a day.
• Locations displayed in ArcGIS, a Geographic Information System (GIS), and loaded onto handheld GPS units to guide field teams to clusters.
• Paired motion-triggered video cameras (Bushnell) recording 60-second clips with a 30-second delay; recording time was limited by full memory cards when animals were busy and by battery life in extreme cold.
• Hourly temperatures from a SNOTEL weather station; canopy cover measured over each carcass with a spherical densiometer.

7. Implications for conservation (from the paper)

• Large carnivores that provide large carcasses are in sharp decline. Carrion from people (hunters, landfills, cities) comes in pulses or in limited areas, so it does not replace what predators provide.
• The authors urge conservation scientists and managers to give priority to working populations of puma-like felids, for example through lower hunting quotas and measures to reduce conflict over livestock, as a way of keeping carrion, and the biodiversity it supports, in natural systems.