Competition Between Carnivores: Untangling the Relationship Between Pumas, Black Bears, and Deer

A black bear looking up from feeding (Photo by Max Allen)

By Max Allen of the Santa Cruz Puma Project

A black bear looking up from feeding (Photo by Max Allen)

Pumas and black bears are the two large carnivores found throughout California. Both species kill deer and other ungulates and as a result they often compete with each other. In Mendocino National Forest, where I completed my PhD project, black-tailed deer, including adults and fawns, make up the vast majority of puma diets. In contrast black bears only prey on fawns, although fawns can make up a large part of their diet during spring and summer. Since pumas prey on both adults and fawns year-round while bear predation is restricted to young fawns, it would be easy to assume that pumas are more responsible for the dynamics of ungulate populations than bears. However, this is leaving out an important part of the story.

While bears do hunt and kill prey themselves, they also frequently scavenge dead animals that have been killed by other predators, such as pumas, or that have died from other causes. Bears’ strong sense of smell helps them locate carrion, while their large size make them a dominant scavenger as they can both usurp and defend the carcass from other animals. One focus of my Ph.D. research was trying to understand how bear scavenging affects puma feeding behavior. In order to do this I visited puma kills to determine how often bears were present, and I placed cameras on fresh puma kills and compared behaviors at those with and without bears.

A black bear feeding on a deer it usurped from a puma (Video by Max Allen)

What I found surprised me: black bears were having large detrimental effects on pumas. Based on camera data, pumas abandoned over 70% of their kills as soon as —> Read More