History of the Yellowstone's Wolves
Wolves were historically a key species of Yellowstone National Park, but due to wild trophy hunting and conflict with ranchers, the species became locally extinct in the 1920s. With the removal of the park's most prolific carnivore, the ungulate population, particularly the Yellowstone moose, skyrocketed. This was a concern for local park authorities as the unsustainable ungulate population had led to excessive grazing. Already in 1930 there was a comprehensive deterioration of the habitat. Numerous attempts to control the elk population through trophy hunting had proved cumbersome and ineffective. Luckily, the gray wolf was considered a national "endangered species" at the time, and conservationists worked tirelessly to revive the world's most widespread canine species.
As part of this conservation effort, 14 wolves were originally relocated from Jasper National Park in Alberta, Canada. The resettlement took the form of a soft release, with the 14 wolves temporarily housed in three makeshift accommodation pens. Moose carcasses were regularly placed in the enclosure to aid in acclimatization to the habitat. The wolves were then released to roam the reserve freely. This resettlement was part of a much larger project that stretched across the Greater Yellowstone Landscape and the neighboring state of Idaho. By the end of 1996, a flock of 66 wolves had been released into the said area. The project has been overwhelmingly successful as the region's wolf population has surpassed 1,000 individuals in two decades. Meanwhile, Yellowstone National Park seems to have reached its carrying capacity. The wolf population within the park has ranged from 83 to 108 as of 2009.
Effects on the ungulate population
The effects of this exponential growth in the wolf population were evident almost immediately. Moose, which are wolves' main prey, have seen a drastic decline in numbers. Between 1995 and 2008, the moose population halved from 17,000 individuals to 8,000. The population has since stabilized at this point. The sheer reduction in ungulates directly greatly reduced the browsing pressure on local flora such as aspen and poplar and reduced habitat degradation immensely. In fact, a study by the U.S. Geological Survey in Fort Collins found that uncombed willows had 10 times greater biomass than their combed counterparts. The wolves that were killed were also crucial for nutrient recycling. A study of 36,000 moose kills spread over 50 years in Michigan's Isle Royale National Park showed that the area around the moose kills had a 12-fold increase in nitrogen deposition.
In addition, due to constant fear of predators, moose herds were constantly migrating to newer areas, leaving former feeding grounds. This would allow degraded habitats to regenerate properly. One such habitat were the riverbeds. The regenerated vegetation was essential in stabilizing the riverbeds, which drastically improved river dynamics. The canals became narrower, meanders lost their meaning, and there was an increase in puddles on the banks. These changes provided excellent wildlife habitats.
However, the rivers were affected in more ways than one. The increase in grazing on the riverbeds allowed for the revival of local populations of the North American beaver (Castor canadensis). At the time of resettlement there was only one beaver dam. This can be attributed to the lack of grazing caused by overgrazing by ungulates in the pre-wolf era.
The increased vegetation was also essential for black bears, which were provided with an increased supply of berries. Songbirds and fruit eaters also recorded an increase in population.
Increased hunting of ungulates indirectly impacted many other species as well. Species such as the American bison have seen steady population increases due to less competition from moose and a lack of predation from wolves. The increase in carcasses was also beneficial for numerous scavengers such as golden eagle, titmouse, shrew, great gray owl and 445 beetle species. In fact, predators such as mountain lions, coyotes, and American black and brown bears also feed on these carcasses.
This was evident in a study that found that 84% of wolf-coyote interactions in Yellowstone occurred during kills. Similar trends have been observed in interactions between bears and wolves. The increase in carcasses would increase the food supply for the various predators in the park, thus contributing to the increase in their populations. This, in turn, would increase the ecological impact of wolves on the reserve.
Effects on scavengers
The wolf populations also acted as a buffer against climate change in Yellowstone. As a result of climate change, winters are becoming shorter and snow depths lower. This allows the herbaceous plant to regenerate more quickly, making it easier for the moose to forage. Reducing energy use would reduce the chances of a moose succumbing to the harsh winter. This could prove devastating for the scavengers that rely heavily on these natural deaths for their food. Luckily, wolves have reduced this impact significantly, as moose make up at least 90% of wolf diet in winter. This was proven by a 50-year study of carrion availability during the winter months in Yellowstone. In areas where the presence of wolves was unknown, carrion availability was reduced by 66% in the late winter months of April. In comparison, the densely populated areas of the park saw only an 11% decrease in carrion availability. While wolves certainly cannot fully mitigate the effects of climate change, the species does offer scavengers an opportunity to adapt to the changing ecosystem.
Influence on coyotes
However, there is one specific species that has a unique relationship with wolves due to their small size. Coyotes can only hunt moose calves and smaller rodents. Populations of moose calves and rodents are greater in the spring months. This means that coyotes depend heavily on wolf kills during the winter months as hunting is impractical. However, the predation of coyotes by wolves is also well documented. In fact, a 90% decline in the coyote population has been recorded within wolves' range. This, in turn, has proven beneficial for pronghorn, which are heavily preyed on by coyotes. A study published by WCS in the journal Ecology showed that fawn survival rates were only 10% in areas with higher coyote populations. This is compared to a 34% survival rate in areas where wolves were plentiful. In addition, on numerous occasions, pronghorns have been observed giving birth near wolf dens. This explains the 50 percent increase in the pronghorn population following the reintroduction of wolves in 1995. There was also an increase in rabbits and mice, among other small rodents, due to the reduction in coyote populations. This would allow for an increase in populations of smaller predators such as weasels, foxes, badgers and birds of prey.
But fabulous as the ecological restoration was, the reintroduction of wolves met with considerable resistance from ranchers and hunters alike. Trophy hunters were disappointed due to the increased hunting restrictions. They also argued that wolves would wipe out entire moose populations. However, a study between 1995 and 2001 at the park showed that 57% of the moose hunted by wolves were old and frail adults, with an average age of 14 years. This would not cause significant demographic imbalances and impede population growth as these individuals were past their reproductive age. Meanwhile, outside of the park, trophy hunters typically target female individuals with an average age of 6 years. This is the prime reproductive age for female moose. The removal of healthy breeding individuals is more destructive to future moose generations.
Ranchers feared that reintroducing wolves would increase human-wildlife conflict due to increased livestock mortality. Wolves were responsible for 569 cattle and sheep deaths in the western US, although this accounts for less than 1% of the region's cattle deaths. Increased stress in cattle due to increased harassment by wolves also resulted in a 30-50% reduction in biomass. Retaliatory killings are also common. However, no concrete statistics have been found on human-wolf conflicts in Yellowstone National Park. In addition, the wolves have proven to be a major tourist attraction, driving ecotourism revenue to $35 million a year. The bulk of the proceeds would be distributed to the local community in the form of jobs and an increased reach of businesses, increasing tolerance for wolves in the neighborhood.
In conclusion, while translocating keystone species has been a challenge, the success of wolf reintroduction bodes well for a sense of hope for the future of conservation. Projects like Rewilding UK and India'sCheetah reintroduction plancan be inspired by the success of Yellowstone National Park. Also, India could be encouraged to protect its population from Gray Wolves to save itdying meadows.
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First published on Think Wildlife Foundation.