When there’s not enough wild prey, lions and tigers and other big cats start killing livestock. Seems straightforward enough. But at exactly what low level of prey density do these predators begin hunting cattle, goats, and sheep? Researchers crunched the numbers and found that when wild prey biomass drops below specific thresholds, cows can expect to be killed first. The smaller ones get eaten later. The findings are published in the upcoming issue of Biological Conservation.
While the density and biomass of livestock far exceed that of wild prey in general, big cats still prefer the latter, likely to avoid retaliatory or preventive persecution by humans. Lions, tigers, leopards, jaguars, snow leopards, pumas, and cheetahs are some of the best-known carnivores responsible for conflicts with people, and almost all of them are either endangered or threatened (only pumas have a “least concern” status).
To help identify conflict hotspots and better target conservation efforts, a team led by University of Göttingen’s Igor Khorozyan wanted to figure out at what prey levels attacks on livestock are triggered. They searched for peer-reviewed publications on wild prey density and livestock predation dated between 2000 and 2014. The focus was on hoofed mammals since they’re a staple for big cats, but smaller animals like capybaras, anteaters, caimans, and hares were also included. The team ended up with 107 studies spanning dozens of countries.
Cattle predation is high when prey biomass drops to 812 kilograms (1,790 pounds) per square kilometer (0.4 square miles). Cows are optimal when it comes to net energy maximization. But when prey biomass dwindles below 544 kilograms (1,199 pounds) per square kilometer, even cows can’t compensate for the lack of food, and the cats start hunting sheep and goats as well.
This reliance on livestock happens regardless of the species, body mass, and population density of the big cats. Even snow leopards, the smallest, most light-weight of them, can actively kill cattle. And all of the big cats (except for tigers) are eager to kill sheep and goats.
Next, as a confirmation, the team mapped out cases with known prey biomass and compared actual livestock predation with threshold-predicted predation. With a few exceptions, their thresholds were reliable predictors. The researchers also found that some protected areas in India, Nepal lowlands, and South Africa contain sufficient prey; but for everywhere else they sampled, prey biomass isn’t high enough and the probability of livestock predation is moderate to high.
Big cats can’t survive when prey biomass plummets to seven kilograms (15 pounds) per square kilometer. There is, however, one gruesome exception: Leopards can keep high densities in prey-free, human-dominated areas by killing domestic dogs.
Image in the text: Matt Gibson/shutterstock