It’s May 2020. As we reluctantly continue to hunker down in our home dens, almost all the grizzly bears in the Greater Yellowstone Ecosystem (GYE) have emerged from theirs. Most anticipated by many wildlife fans are the class of 2020 — the COYs, or cubs-of-the-year — facing their first spring. There may not be many humans to watch them this spring in Yellowstone and Grand Teton National Parks, but their protective mothers have that covered. What’s going to happen to the class of 2020 in the upcoming years? Let’s choose fifty cubs born this year from across the GYE and follow their hypothetical fate into the future.
First, a little background. Their parents courted last year, in late spring or early summer 2019. Grizzlies are not monogamists; in fact, each cub in a litter of three could have a different father. The fertilized embryos did not implant in the uterine wall until late November or early December. From then, it was just two months before the newborn cubs were born (late January or early February). At the time, they were not much bigger than a soda can. They nursed and grew in the den until it was time to face the outside world in April.
From the moment they see their first sunlight, a grizzly cub faces a world that is full of delights like gopher caches of roots and rotting elk carcasses. Their world is also full of dangers. Cub mortality is high and the most dangerous time of a cub’s life is the first few months. In the Greater Yellowstone Ecosystem, the average litter size is about two and a half cubs born per female, but by the time they are counted later in the summer, the average is only two. That’s a 20% loss just in the first few months. By the time Fourth of July fireworks light the skies of communities across the outskirts of the ecosystem, we are already down to forty cubs.
Other bears, particularly mature male grizzlies, are one of the biggest threats to cubs. Male bears have their own logical motivations for an act that is horrendous from our point of view. Losing her cubs can prompt the mother to enter estrus (also known as being “in heat”), so he may breed with her and replace a rival male’s genes with his own. There’s some evidence that males will tolerate their own cubs at a shared carcass, so he may know which cubs might be his from familiar females and which cubs are from strange females that can’t be his. Maybe by targeting cubs from unknown females, he gives his own cub a better chance of survival by eliminating the competition early in the game. And finally another bear, whether cub or adult, is always a potential meal for the opportunistic and occasionally cannibalistic grizzly. As sad as it is to see, this is how nature adjusts bear population to the food resources in the ecosystem. As grizzly density increases, cub mortality rises. Starvation as a result of competition with other bears is also a cause of cub mortality. There are other natural dangers such as predation by wolves or drownings in river crossings.
As we move from some of our cubs in the heart of Yellowstone to some of our cubs from less dense populations on the edge of the Demographic Monitoring Area (DMA), the cubs are less likely to face predation by other bears – but this is replaced by an increased likelihood of human-caused mortality on the periphery of the DMA. The majority (but not all) of these are caused by human-bear conflict with the cub’s mother. When the mother dies, the cubs will as well: either to also be killed at the same time, to die later as orphans from the loss of the food and protection of their mother, or to be removed from the breeding population for a life in captivity.
By the time the cubs enter the den with their mother in late fall or early winter this year, we are down to twenty-eight cubs. Most grizzlies across the GYE will spend the next full year with their mother as yearlings. Their increased size gives them some advantage over the 2021 COYs, but they still face the same threats they did the previous year. They hibernate with mama bear one last time, and by the time the two-and-a-half-year-old cubs are booted from their mother’s side in spring 2022, we are down to fifteen surviving cubs.
If these young bears – no longer cubs, now called subadults – are lucky enough to spend the majority of their time in places like Yellowstone National Park where the chance of conflict with humans is relatively low, the riskiest part of their life is over as they look towards adulthood. A wild grizzly can live past twenty years old, and the annual survival rate on both male and female grizzlies in the ecosystem has averaged 95%.
But as we follow the fate of our subadults, if the 2020s and ’30s follow the trend of the last few decades, the majority of our fifteen grizzlies – about 80-85% of documented grizzly mortalities – will be killed by humans. That’s about twelve of the fifteen bears that were both lucky and tough enough to survive their cubhood.
How will those twelve bears meet their end? Five of them (about 30% of all grizzly mortalities, both natural and human) will be killed in conflict with people hunting elk or other game. Three of them (about 25% of all mortalities) will be killed in conflict with humans in developed areas, for actions such as feeding on pet food or apple orchards. Two more (about 19%) will be killed for going after livestock, mainly cattle. One of the remaining two is hit by a car and another is illegally killed by a black bear hunter. There are other ways grizzlies meet their end through human means, but the big three are encounters with ungulate hunters, habituation in residential developments, and conflict with livestock.
From the 1970s to the 1990s, fewer than twenty bears were killed by humans each year. In the mid-2000s, that number doubled to over forty as the bear population began to expand towards the edges of the Demographic Monitoring area. In the last five years, that number has occasionally risen above fifty. It takes fourteen years for a grizzly just to replace herself in the ecosystem, so every unnecessary loss impacts the population.
It’s hard news to stomach, that our tough little survivors face a threat that, as powerful and intelligent and adaptable as grizzlies are, they are just not equipped to avoid. Bears follow their stomach and their stomach sometimes tells them to raid a birdfeeder or claim that hunter-killed elk – with lethal results for the bear. The good news is there is an animal even more intelligent than a grizzly: a human being.
We have it in our power to lower the number of grizzlies killed by humans each year. People recreating and hunting in the backcountry can carry bear spray and know how to use it effectively. People living on the edges of bear country can keep pet food indoors, set up electric fences around orchards, and keep their trash in the garage. Ranchers can select calving areas away from areas of likely grizzly activity if they have the option to do so, keep carcasses away from cattle, and deploy range riders to monitor the herd.
The fate of our fifty cubs is all still hypothetical. Those fifty cubs are roaming the landscape now: playing king-of-the-log with their siblings, finding out that beetle grubs are edible and rocks are not, and learning about the natural (or residential, or agricultural) landscape around them. Many of these cubs naturally will not make it, and that is the reality of most young wild animals from meadow voles to grizzly cubs. But for our class of 2020 that makes the journey through the perils of cubhood and become adult bears, their fate is largely in our hands.