Last month, we turned our spotlight on the underappreciated ungulates of Asia’s high mountains and their significance beyond being mere prey for snow leopards. Unfortunately for ungulates, this month we are discussing the ideal meal for snow leopards: ibex. Specifically, fully grown ibex males in the prime of their lives.
This preference for large prey is unusual behavior for large cats, who tend to prefer and hunt prey typically smaller or similar in size to them. For perspective, a fully grown male ibex can exceed 100 kg, more than twice the body mass of an average snow leopard. Unlike most big cats, male and female snow leopards are similar in size, showing minimal sexual dimorphism.
Our study shows that snow leopards prefer large male ibex, while female ibex, which are much closer in size to snow leopards, were selected less frequently than their relative population abundance would suggest. Similarly, young male ibex under six years old and yearlings between one and two years were also hunted by snow leopards at unexpectedly low rates.
Prey selection by predators is influenced by many variables, including seasonality. We tracked prey selection across the four seasons and still found that adult ibex males were selected at higher than expected rates. Spring saw the only significant change in this selection, when male snow leopards hunted female ibex and female snow leopards hunted ibex kids at higher rates. This shows that snow leopards are dynamic hunters, adjusting their prey selection based on seasonal vulnerability in ibex. “Young ibex kids haven’t yet developed the agility and speed needed to escape, while adult females lose much of their agility in late pregnancy, making them both easier targets,” says Dr. Örjan Johansson, SLT’s Senior Scientist and lead author of the paper.
But why male ibex?
We expect predators to select prey that will give them the most bang for their buck – or, in scientific terms, the highest energy gain. Yet, in our study, we found that younger males, which have the second-highest biomass of all ibex age-sex classes, were hunted at lower rates than their relative population abundance would suggest. This implies that snow leopards were choosing the older male ibex for reasons other than their large biomass. Are older ibex perhaps more vulnerable to snow leopard hunting strategies?
Ibex horns continue to grow as they age, with older males typically having the largest horns. While this gives them some advantages (we’ll get to that soon), it is not a great boon while being chased down a mountain by an ambushing snow leopard. The big bodies and large horns of the mature male ibex seem to make them more vulnerable to predation in the crags and crannies of their mountainous habitat. This “handicap” is, oddly enough, a great boon for many other potential prey species, whose “weapons” (horns, in this case) and large size would make them safer from predators.
You might ask, then, why does nature select for big bodies and horns, if it makes ibex more vulnerable to predation? Well, mating. Ibex establish dominance during their rutting, where big bodies and horns generally come out on top. It’s an interesting tradeoff for the ibex males. What makes them more likely to mate – large body and large horns – also makes them more vulnerable to being eaten. “Their size and horns make them more dominant in the competition for females, but also increase their risk of being caught by snow leopards. This could be an example of a sexually selected handicap – where traits that improve mating success come with a cost,” says Örjan. So bigger is better, until it’s not.
These findings document unusual hunting behavior by snow leopards and further our understanding of their prey selection and how they utilize rocky terrain to their advantage. It calls into question the viability of “trophy hunting” of ungulates as a conservation tool, as it appears both snow leopards and trophy hunters value the same prize, which could put pressure on ibex populations. The study itself is also unusual, because it gives us rare, detailed insights into snow leopard prey selection.
Our scientists achieved something remarkable by studying 150 kill sites and tracking nearly 4,000 ibex over different seasons, allowing them to understand not just what these elusive cats hunt, but specifically which ages and sexes they select depending on the season.
DID YOU KNOW? This study was able to gauge the ages of ibex based on their horns. Like tree trunks, ibex horns grow larger each year, and a new ring indicates a new year!
Photo credits: Prasenjeet Yadav, Örjan Johansson for Snow Leopard Trust/SLCF-Mongolia
Acknowledgments: This long-term ecological study is in collaboration with Snow Leopard Conservation Foundation in Mongolia and Snow Leopard Trust, with special thanks to the Ministry of Nature, Environment and Tourism, the Government of Mongolia, and the Mongolian Academy of Sciences for their support.
We would also like to acknowledge: Acton Family Giving, Bioparc Zoo de Doue la Fontaine, David Shepherd Wildlife Foundation, Idaho Falls Zoo at Tautphaus Park, John Ball Zoo, Kolmårdens Zoo, Korkeasaari Zoo, National Geographic Society, Nordens Ark, Parco Zoo Punta Verde, Play for Nature, Tierpark Berlin, The Big Cat Sanctuary/Wildlife Heritage Foundation, Tulsa Zoo, Whitley Fund for Nature, Zoo Basel, Zoo Dresden, Zoo New England and the many incredible partners who have supported programs like our Long-term Ecological Study and research in Mongolia since it began in 2008. We could not do this work without you.