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.
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.
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.
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.
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