F51, an adult female mountain lion currently followed by Panthera’s Teton Cougar Project, has given birth to three litters in three years, which as far as we know, is something of an anomaly. F51 immigrated into our study area from some unknown place and we started tracking her at the very start of 2011, just before she gave birth to her first litter (5 kittens!). In fall 2012, she separated from her kittens when they were 14 months old, and then she gave birth to three kittens, just 16 months after her first litter. Wolves killed two kittens from her 2012 litter when they were very young, and when her last remaining kitten was just nine months old, they went their separate ways. We were completely baffled as to why such a young mountain lion was on her own (typically kittens disperse at about 18 months in our study area), but the answer revealed itself a month later. Just ten months after her 2012 litter, F51 gave birth to four new kittens in 2013. Absolutely amazing, and completely unexpected.
Watch the video below of F51’s 2013 litter when we discovered them (unexpectedly, during routine filed work looking for mountain lion kills). They are two days old.
Fecundity. I’ve always liked the sound of the word, and how it feels when I say it. According to Merriam-Webster’s Collegiate Dictionary, fecundity means “fruitful in offspring.” For biologists, fecundity is a measure of how fruitful is a species. It’s also essential knowledge in understanding species ecology and creating effective conservation plans for species that need support. For wildlife researchers, quantifying fecundity is something of a holy grail, because it requires such a significant time and energy investment, a quest if you will.
What information is needed to determine fecundity for an animal, you might ask? First, we need to know how many offspring are born at a time. Is it typically one offspring, like humans, or twins like pronghorn? Second, we need to know how often a single female gives birth. Females of many species give birth every year, or several times a year, in cases such as meadow voles and cottontail rabbits. Last, we need to know how long females typically live in a population to estimate how many times she might give birth during her lifetime. Seems so simple!
Now let’s consider mountain lions. Cougars are cryptic carnivores that earn a living by remaining invisible to their prey. They live like shadows on the landscape, weaving in between us, often unseen. They wander vast areas as they hunt and survive, making it challenging to predict where they are at any given point in time. Mountain lions are difficult to see on a normal day, but especially tricky to see when giving birth. And mountain lions live eight to 12 years, and sometimes longer (except in hunted populations). So how do we go about finding cougar dens, documenting the length of time between cougar litters, and determining the average length of time a female cougar survives in the wild?
It would be a near impossible task, if not for technology that allows us to follow mountain lions in the field—I’m talking about the collars researchers place on animals. Modern GPS collars allow us to not only pinpoint the location of an animal, but to do so in near-real time, because GPS locations are transferred through satellites to computers in our dingy field offices.
But let’s jump to what we’re learning on the Teton Cougar Project, one of few long-running projects on mountain lions. Unfortunately, many research projects are short—typically the length of a MS or PhD program—and thus determining fecundity for a species like mountain lions is impossible. Projects like the Teton Cougar Project are so special because they are so rare.
Over 13 years, we’ve visited the natal dens of 18 different females to document litter size, and recorded inter-birth durations for nine females for which we documented two to three consecutive litters. Here, in the Southern Yellowstone Ecosystem in northwest Wyoming, female mountain lions give birth to an average of three kittens (range two to five) on average every 27 months (range 10 to 39 months). It’s amazing how so much work and so many miles hiked can be summarized in just a sentence or two.
F51 is certainly our most “fruitful” female to date. Follow F51 and other mountain lions on facebook.