In the wild, very little is known about snow leopard birth rates, litter size and survival rates. Understanding this reproductive data is crucial for determining whether populations can sustain themselves through various environmental pressures and fluctuations. For example, what are the chances that a snow leopard population will be able to persist if some individuals are lost to disease, poaching or a decline in prey populations?
Given these knowledge gaps, the opportunity to document wild cubs in their den is invaluable to science and conservation strategies. Snow Leopard Trust Senior Scientist Dr. Örjan Johansson explains why we visit den sites of GPS-collared cats and what happens during the process:
We primarily use motion-activated camera traps to quantify litter size and cub survival. However, cubs don’t start accompanying their mothers regularly until they’re about five months old, which means we rarely observe them in our cameras before this age. We can calculate survival rates between 6 months and 18 months of age, since cubs stay with their mothers for 20-22 months. But the only way to assess litter size, survival rates from birth to 6 months, or whether any litters are lost at a young age (before 6 months) is by visiting dens to count the cubs directly.
Cub survival in other large cats can be rather low in the first months of life. For example, common leopards can lose more than 50% of their cubs before 4 months of age due to infanticide. We believe snow leopards differ from other big cats in that infanticide appears to be very rare. To confirm this, we need to estimate cub survival from birth or soon after.
Unlike other big cats, snow leopard mating is highly seasonal and only occurs from January to March. After a three-month gestation period, cubs are born between April and June. In the days before giving birth, females may restrict their movements somewhat, perhaps while searching for a den site or because they’re too heavy to hunt effectively in steep terrain. Snow leopards appear to select caves in terrain that’s too steep for wolves but not so steep that cubs will fall when they start walking. However, there doesn’t seem to be a fixed rule for what makes an ideal den, and perhaps any sheltered location will work.
When the female is in the den, the ‘roof’ prevents the GPS collar from communicating with the satellites, which means that for us, the female ‘disappears’ when she gives birth and in the following days of intensive nursing. We check locations of our collared females more or less every day during the denning period to detect any sign of denning as early as possible. Ideally, we want to visit the cubs when they are roughly three weeks old. At that age, they are fairly big (1.5-2 kg), the bond between mother and cubs is fully developed and yet the cubs are not large enough to crawl/walk and hide when they hear us approaching the den.
Within a few days of giving birth, the female starts leaving her cubs in the den and going out to hunt for prey. When we plot the GPS locations from her collar and connect them with lines, a pattern similar to a bicycle wheel emerges—with the den as the hub and the spokes showing her movements back and forth between kill sites and the den. This makes it relatively easy to identify the general area where the den is located, though pinpointing the exact location can be challenging since we don’t receive GPS signals when the female is inside the den.
This summer, F12 gave birth on June 1 and F19 gave birth on June 11. We were fortunate this year to receive many GPS locations concentrated in a small area for both females, allowing us to narrow down potential den locations to approximately 30 x 30 meters for each site.
On our first day in Tost, we planned to find observation points far enough from the dens to pick up radio signals from the females’ collars without disturbing them. This would help us determine whether they were in the dens or away hunting. We obviously need to wait for them to leave before we can safely approach the den sites.
We drove to F12’s area first. Despite listening from locations where we should have picked up signals, we couldn’t detect her, so we hiked closer. When we were 400 meters away from the den and still receiving no radio signals, we concluded she was away.
Once we found the den, we gently collected the cubs and placed them in a burlap bag—they typically relax and stay calm when it’s dark and they’re together. F12 had two cubs, a male and a female, both weighing 1.8 kg and in good health at 28 days old. Besides counting, weighing, and determining sex, we collect saliva swabs for DNA analysis and insert tiny microchips under the skin that enable us to identify them if we capture them years later as adults for collaring purposes. The tagging only takes a few minutes and we try to disturb as little as possible.
After finishing at F12’s den, we drove to F19’s location to listen for signals. She was also away, but we decided not to enter because it was getting late and the VHF equipment would shut down 50 minutes after we arrived. Using range finders and a compass, we assessed the bearing and distance to the suspected den and got a good look at the area, identifying three possible caves.
Up until this point, F19 had been leaving the den during daytime for the past four days, feeding on a huge 13-year-old ibex male that one of our other collared snow leopards, M24 Angarag, had killed on June 23rd. F19 found him at the kill site two days later, and they fed together for three days. (M24 is relatively young and unlikely to be the father of these cubs. The similarly-sized F19 probably took advantage of an easy meal near her den and may not have given the younger male much choice about sharing.)
For the following three days, she remained in her den, so we didn’t approach. But on July 3rd, F19 was away when we arrived at our listening site. We found the suspected den area, which was considerably steeper and higher up than F12’s location. Her three cubs were in a cave—two males and one female—all weighing 1.7 kg and appearing to be in good health.
Following our visits, we confirmed that both females returned to their dens and continued using them. We always monitor the sites afterward to ensure our careful methodology preserves normal denning behavior patterns. (Note: We do not disclose their locations or provide maps that could be used to identify where the dens are located.)
In a world where snow leopards face mounting threats from illegal hunting, climate change, habitat loss, and retaliatory killing for livestock predation, every snow leopard cub born in the wild matters. These are only the 6th and 7th den visits of wild snow leopard cubs since our long-term study launched in 2008 (all of them in Tost, Mongolia). Indeed, they are the only den visits scientists have ever documented worldwide. Data from these rare encounters is vital for understanding snow leopard ecology and making informed conservation decisions to secure their future.
You can help snow leopard cubs in the wild by adopting your own plush cub. For a limited time, you’ll receive an exclusive photo print of the wild cubs in this story as a thank you for your support. All adoptions fund our conservation efforts.
Photo credits: Snow Leopard Conservation Foundation/Snow Leopard Trust
Acknowledgements: 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.
This is wonderful! Those babies are so cute! ☺️