A Fortress For Cougar Kittens

Two of four kittens born to F47 in 2013, an adult female mountain lion in northwest Wyoming.
Two of four kittens born to F47 in 2013, an adult female mountain lion in northwest Wyoming.

We suspected F47, an adult female mountain lion followed by Panthera’s Teton Cougar Project, was pregnant in Spring of 2013; during the winter, we had caught her on camera consorting with M85, the resident male that overlapped her territory (see Rare Video Footage Shows the Dynamics of Cougar Courtship). In late Spring, F47 began to make large loops about her home range characteristic of pregnant females—perhaps she was seeking that perfect place to give birth where she felt safe from predators, or perhaps she was driven by discomfort or hormones…who can say for sure. But like clockwork, 90 days after the intimacy she shared with M85 during winter, she stopped traveling; she did not move for 10 full days in early June.

Several weeks later, F109 gave birth to a new litter as well. One of the endless fascinating quirks about mountain lions is that unlike bobcats and Canada lynx, they can mate and give birth at any time of year. But in truth, they typically don’t, at least in the temperate environments in the Northern Rockies of North America. Several researchers have shown that cougars tend to exhibit a birth pulse in summer (Ruth 2004; Jansen and Jenks 2012). Researchers speculate summer births allow mountain lions increased food availability during the period when deer, elk and other ungulates give birth as well. Young deer and elk are particularly vulnerable to predators and generally easier to catch and subdue than their parents.

Thus the timing of dens is of paramount importance, but so is location. The significance of selecting a fortified den site–meaning the physical fortress forming the protective walls around the female and her offspring—could not have been made more apparent that in comparing the dens of F47 and F109 in 2013. F47’s den was the more difficult to reach by far, a 2.5-hour drive and then a 5 hour hike to reach the spot she selected on the southern edge of our study area. We waded waist-deep across one river strewn with beaver dams and lodges, crossed open sage brush and then traversed a mountain side, ever angling up towards the highest forests. Near the top of the mountain, we entered an area where a small landslide had toppled trees, as well as created great gashes in the forest floor and just the sort of upheaval ideal for creating log jams, earthen folds and other chaos well suited to fortified dens. We peered in more than a dozen ideal dens (at least they were ideal from our perspective!) as we approached the GPS locations betraying her choice. We were shocked to find the kittens lying in a pile in an opening within a clump of young fir trees. Such was the lack of physical protection, that we could spot them from a distance and walk right up to the kittens to count them and assess their health. Mosquitoes swarmed the four tiny kittens, feeding lazily from eyelids and noses and every other available source. The kittens roused at our approach and greeted us with hisses. But they were so young they were unable to move away or to defend themselves in any way.

F47's 2013 den in a clump of fir trees. The kittens are visible, huddled in a clump and completely vulnerable to predators. Photograph by Mark Elbroch / Panthera.
F47’s 2013 den in a clump of fir trees. The kittens are visible, huddled together and completely vulnerable to predators. Photograph by Mark Elbroch / Panthera.

F109, in contrast, selected an impenetrable tangle of dead branches created by trees that fell in a great storm. I had to crawl on my hands and knees through a 10-ft tunnel of stabbing branches before I reached the chamber in which she gave birth and nursed her newborn young. The posterior of the den offered a labyrinth of smaller tunnels ideal for wiggling kittens needing to escape larger predators. It was the perfect den, in terms of defense.

The open area inside F109's 2013 den where she gave birth and nursed her newborn kittens--surrounded in tangled walls of downed wood. Photo by Mark Elbroch / Panthera.
The open area inside F109’s 2013 den where she gave birth and nursed her newborn kittens–surrounded in tangled walls of downed wood. Photo by Mark Elbroch / Panthera.

Between 2002 and the end of 2013, we documented den site descriptions for 23 dens, and timing for two more. Seventeen dens were located in deadfall (horizontal dead trees), two were in caves created by boulders in scree slopes, three were in brushy thickets, and one was in a relatively open clump of young fir trees in forested habitat (F47’s 2013 den). Just as in previous studies, the timing for these 25 dens was clumped in summer (see figure below), with 56% of 25 dens beginning in June or July. The earliest birth date we recorded was May 20th and the latest parturition was November 3rd, which based upon a 3-month gestation period (pregnancy), suggests a courtship period in northwest Wyoming beginning in late February and ending in early August (see figure below). These findings and additional information about den selection were just published in Mammal Research (formerly Acta Theriologica)—a link to the full article can be found here. If you are interested in reading the article, please feel free to contact us through our facebook page, and we’d be happy to send you a copy.

Timing of cougar dens and associated breeding season in northwest Wyoming. Figure by Mark Elbroch / Panthera. (Originally published in Elbroch et al. 2015. Mammal Research)
Timing of cougar dens and associated breeding season in northwest Wyoming. Figure by Mark Elbroch / Panthera. (Originally published in Elbroch et al. 2015. Mammal Research)

When F47’s kittens were 4-weeks old, she moved them north in the direction she’d been hunting. We don’t know why, but she only moved three of her four kittens to a spot which only offered moderately better protection to her family (we assume the fourth kitten died, but we never found the body). At 5-weeks old, she moved her remaining three kittens to the site where she had killed an adult mule deer. She stashed them in a clump of loose bushes at the base of a massive pine tree about 70 yards from the kill. She moved between the deer carcass and her kittens with great regularity.

A large black bear discovered the deer carcass several days later, and then followed F47’s back trail to her kittens. The sparse bushes provided absolutely no physical barriers to the bear; F47 had left them vulnerable. He killed each one, consumed their tiny milk-filled bellies, and discarded their tails and crushed heads. F47 fled the scene and wandered for near two weeks, during which we did not detect any evidence that she killed new prey; twice she looped back to the site where her kittens were killed. Perhaps it was shock that drove her, but we cannot be certain. (Note: F47 had lost her previous litter to a wildfire, but as of writing this blog, she is mother to two kittens born in summer 2014—her first successful litter ever.)

When they were just 3-weeks old, F109 began moving her kittens as well. She led them from one fortified logjam to another, moving them every other night, higher and higher up the mountain into more rugged, difficult terrain. They were with her when she killed a wolf, described in Hunters or Hunted? Wolves vs. Mountain Lions. They grew and played and became healthy young mountain lions (see video below, in which they squabble around a beaver carcass killed by their mother, when they were 4-months old). Its no doubt that F109’s selection for rugged terrain and fortresses of interwoven logs helped keep her kittens safe. Though the same age as F47, F109 has raised three successful litters to date—meaning at least some kittens from each litter succeeded in setting out to find territories of their own.

Additional information about litter sizes and the frequency with which females give birth are included in Fecundity and Cougar Kittens. Continue to follow F47 and F109, and the adventures of other mountain lions as well, on our Panthera Puma Program facebook page. Thanks for reading.

Panthera logoElbroch LM, Lendrum PE, Alexander P, Quigley H (2015) Cougar den site selection in the Southern Yellowstone Ecosystem. Mammal Research (formerly Acta Theriologica) doi: 10.1007/s13364-015-0212-6

Jansen BD, Jenks JA (2012) Birth Timing for Mountain Lions (Puma concolor); Testing the Prey Availability Hypothesis PLoS ONE 7:e44625

Ruth TK (2004) Ghost of the Rockies: the Yellowstone cougar project. Yellowstone Science 12:13–17


  1. Kirsti Addison
    April 18, 2015, 4:10 am

    Are mountain lions territorial? because if they are that could play a role into the type of dens they use for the kittens. Have you considered this?

    • Mark Elbroch
      July 3, 2015, 1:32 pm

      Yes, they are territorial… but I’m not sure I follow you…do you mean that they might be hiding kittens from other mountain lions? Could be, as heavy impacts from infanticide (males killing kittens) is documented in other parts of their range.

  2. Kirsti Addison
    South Africa
    April 18, 2015, 2:59 am

    Hi. I understand how human hunting can affect the population badly. And i wanted to know what theses animals are hunted for, is it ‘religious’/ tribal reasons? and what are people trying to do to stop this?

    • Mark Elbroch
      July 3, 2015, 1:36 pm

      No, not for religious reasons. Its recreational sport hunting, for the most part, encouraged and managed by State agencies looking to control mountain lion numbers. The thoughts one generally hear is that we need to control mountain lion numbers to protect people, livestock, pets, and game species we value (elk and deer), though research doesn’t always support the ideology that hunting succeeds in doing so.

  3. Kirsti Addison
    April 18, 2015, 2:42 am

    Do you think logjam dens are the best dens from the kittens perspective? Would the kittens not have to learn about their surrounding or do they only stay in those dens for a very short period?

    • Mark Elbroch
      July 3, 2015, 1:36 pm

      they are in the dens 5 weeks. I think protection is key at this age, yes.

  4. Sue Edwards
    April 18, 2015, 2:30 am

    Getting the news out there about these beautiful animals its amazing, and could impact alot on the education of people from areas who are not around the Northwest Wyoming.

  5. Kirsti Addison
    April 18, 2015, 2:26 am

    Thank you i will definitely stay tuned! Something that had been bothering me was if there were any other possible reasons (other than death) that F47 would only move 3 of her 4 kittens?

    • Mark Elbroch
      July 3, 2015, 1:37 pm

      Its a good question. F47’s next den was in an incredible log jam, and all 3 kittens survived their youngest months…

  6. Erica
    April 18, 2015, 2:24 am

    Out of you research what is the most occurring den that mountain lions tend to use?

    • Mark Elbroch
      July 3, 2015, 1:38 pm

      logjam, by far.

  7. Kirsti Addison
    April 16, 2015, 1:51 pm

    Thank you I definitely will stay tuned. There was one thing that i have been thinking about and it was really sad how F47 eventually lost all her kittens, but what bugged me more is if there was any possibility (other than death) that she would only move 3 of the 4 kittens?

  8. Sue Edwards
    April 16, 2015, 1:47 pm

    I appreciate the work you do and thank you for always keeping us updated.

  9. Kirsti Addison
    April 16, 2015, 5:36 am

    Hi. Thanks i defiantly will stay tuned. It is very interesting to track the behavior of these mountain lions. I have another question, could there any other possibility (besides death) that F47 would only move only 3 of her 4 kittens?

  10. Kirsti Addison
    April 14, 2015, 5:47 pm

    I agree with the comment above that some mountain lions are more cleaver than others, how ever why is that so? could it be the way they were raised? and why would F47 choose a den that has a lack of protection?

  11. Kevin A
    April 14, 2015, 5:45 pm

    Are there any other factors that we could look at that may increase the survival of these mountain lions?

    • Mark Elbroch
      April 15, 2015, 7:18 am

      In northwest Wyoming, human hunting plays the greatest role in determining the number of mountain lions on the landscape. Then competitors, like wolves. We have been tracking both tese factors very carefully and are just about to publish our results…stay tuned.

    • Mark Elbroch
      July 3, 2015, 1:41 pm

      Birth timing (severe winter weather) is a big one–hard to figure how we might influence this, as its likely related to lots of variables. It is influenced by hunting which reduced males during peak breeding…its often in summer a new male arrives in this study area, due to deep snows restricting winter traveling, and these breeding opportunities result in later litters… but once a female is on a later cycle, she may continue to give birth later… Disease is minimal for kittens… Male infanticide isn’t an issue in our study area, but is elsewhere. Males killing kittens has been linked to hunting and male turnover, but I think there is still a great deal to learn about patterns of male mountain lion infanticide before we really understand it.

  12. Kirsti Addison
    April 14, 2015, 5:41 pm

    I agree with the comment above stating that some mountain lions are more cleaver than others. But is there any possible reasons that F47 chose a den that lacked in protection?

  13. Marcus Grigato
    Blumenau - SC, Brazil
    February 1, 2015, 8:53 pm

    It seems that some mountain lions are more clever than others. Their population could be bigger if many kittens didn´t die so early. But that´s how their lives are. Quite hard!
    Thank you!

  14. Timothy Willis
    United States
    January 27, 2015, 5:52 pm

    Say hi to Casey for me you guys are doing great work.