A changing season means a changing diet for bison

North American bison adjust their diet seasonally in order to take full advantage of the growing season when grasses become less nutritious, a new study led by researchers at the University of Colorado Boulder has discovered.

The findings, which were recently published in the journal PLOS ONE, indicate that bison are not entirely reliant on grass for their nutritional needs and can selectively expand their foraging to include woody shrubs and flowering plants during the spring and fall.

The study sheds new light on variations in the large herbivore's eating habits and may have future implications for management and conservation of bison in Colorado and across the American West.

"We wanted to know if bison might change what they eat as the season goes on and how that affects the microbial composition of their gut," said Gaddy Bergmann, a doctoral candidate in the Department of Ecology and Evolutionary Biology at CU-Boulder. "This study shows that it may be beneficial for the species to have other plants, bushes, and trees available to browse from."

The 166-day study conducted in 2011 sampled a herd of roughly 300 bison living in the Konza Prairie Biological Station in the Flint Hills area of northern Kansas. Bison were reintroduced to the protected native tallgrass sanctuary in 1987.

By sequencing the plant and bacterial DNA found in the bison's fecal samples, researchers at CU-Boulder were able to identify the types of plants that the bison were consuming over time. The researchers found that the bison are willing and able to consume higher quantities of woody shrubs in the early spring and in fall when their preferred menu item--fresh grass--is less available.

The researchers then identified benign gut microbes present in the bison's lower digestive tract and traced how the abundance of those microbes changed over time. Some bacteria became more abundant during the growing season as the bison switched to more energy-rich foods in the summer and autumn.

Other grazing animals throughout the world, such as elk and wildebeests, migrate over long distances in order to follow their food supply. Historically, bison did so as well, but are more sedentary in their range today, making them more susceptible to seasonal changes in vegetation.

While an estimated 20 to 30 million bison once roamed the North American landscape, hunting and habitat encroachment reduced the population to just a few thousand by the end of the 1800s.

Cougars, aka mountain lions and pumas, likely to recolonize portions of habitat in the middle part of the United States

A groundbreaking new study shows that cougars, also known as mountain lions and pumas, are likely to recolonize portions of habitat in the middle part of the United States within the next 25 years. It is the first study to show the potential "when and where" of the repopulation of this controversial large predator.

The study, led by researchers at the University of Minnesota and Southern Illinois University Carbondale, will be published soon in the international journal Ecological Modelling.

This is the first, large-scale population viability study on cougars. The research examined more than 40 years worth of data on demographics and geographical information on more than 3 million square kilometers to determine possible areas of population establishment. The researchers specifically looked at the female dispersal since population settlement is dependent upon the arrival of females in a given area.

"We didn't just look at where they are now, but where they could go," said study author Michelle LaRue, a University of Minnesota research associate in the College of Science and Engineering's Department of Earth Sciences. "These are predictive models, but we feel that our study could be an important tool for conservation of this species and education about a large carnivore that can sometimes incite fear."

Breeding populations of cougars are already living in the Black Hills of South Dakota, and researchers noted four breeding populations in North Dakota and Nebraska. The new study shows that cougars could be expected in the next two decades in Arkansas, Missouri and Nebraska with the potential to sustain existing populations in the Dakotas and Nebraska.

Historically, cougars were once one of the most widely distributed land mammals on earth, ranging from the Atlantic to Pacific oceans and from northern British Columbia to southern Chile. In the United States, the cougars were pushed back to the American West with the arrival of European settlers. Although they have been extirpated for more than 100 years, cougars have been reported in the middle part of the U.S. over the past two decades with more than 800 instances of confirmed cougar presence from 1990-2015.

"The reason cougars used to exist across the country and now they don't is because of people," said study co-author Clayton K. Nielsen from Southern Illinois University Carbondale's Cooperative Wildlife Research Laboratory and Department of Forestry. "Now that this large carnivore is expected to come back into new areas, we need have a clear plan for education and conservation."

The next step is to examine human acceptance and attitudes toward the repopulation of cougars, said LaRue, who is also the executive director of the Cougar Network, a nonprofit research organization.
"We now have the information necessary for government agencies to plan for ecosystem-based management and societal attitudes toward the recolonization of this predator," LaRue said. "Given that cougars are expected to inhabit areas where they haven't been for more than 100 years, this will pose considerable challenges for wildlife managers and the general public in the future."

Mad cow disease changed the diet of the Galician wolf

The Creutzfeldt-Jakob disease crisis in Europe was a turning point for the diet of the Galician wolf in Spain, which until the year 2000 had primarily fed on the carrion of domestic animals. A new study shows that, after European health regulations made it illegal to abandon dead livestock, wolves started to consume more wild boars, roe deer and wild ponies, but also began to attack more cattle ranches when faced with food shortages in certain areas.

With the arrival of bovine spongiform encephalopathy - commonly known as mad cow disease - in Europe, the European Community had to enforce a number of laws in the year 2000 in order to prevent the disease from spreading. Among other things, it became illegal to abandon the carcasses of ruminants that had died on farms; up until then, this had been an important food source for wolves.

From then on, having been adopted by every European country, this measure began to affect a number of scavenger species, especially the vultures that lived on the Iberian Peninsula. But they weren't the only victims; the Iberian wolf (Canis lupus signatus) was also affected.

A team of researchers has analysed the dietary evolution of Galician canines by examining two time periods: before the European law was established (from the '70s up to the year 2000) and afterwards (from 2003 to 2008). Besides this legislation, a combination of other changes also affected the wolves, such as reductions in the quantity of livestock, rural depopulation and the reforestation of agricultural land, which boosted the number of wild ungulates.

The study, published in 'Environmental Management', indicates two very different dietary patterns for the two time periods. While carrion was the primary food source for wolves in the '70s, from 2004 onwards, around the time that legislation was passed to dispose of pig and bird carcasses, their diet underwent drastic changes throughout all of Galicia. The Galician wolf now largely depends on roe deer and wild pony populations.

"We've observed a decline in carrion consumption among wolves, especially in the areas studied in western Galicia, with a reduction of between 57 and 67%, dependent on the season, and a marked drop in the consumption of livestock solely in eastern Galicia (with a reduction of between 66 and 93%, dependent on the season)," Laura Lagos, researcher from the University of Santiago de Compostela (Spain) and co-author of the study, tells SINC.

Roe deer, wild boars and ponies on the menu for wolves

Between 2003 and 2008, the consumption of wild ungulates (roe deer and wild boars) and of wild ponies (Garrano horses) increased. "An increasing number of roe deer and Galicia's significant wild pony population both softened the blow when cattle carrion disappeared, allowing for a change in the wolf's diet and strengthening its predatory niche," says Felipe Bárcena, another of the authors and a scientist at the same university.

Although the roe deer seems to be the wolf's favourite prey throughout the region, different wild animals have been targeted in the different areas of the autonomous community. In western Galicia, an area previously uninhabited by these wild ungulates, roe deer and wild boars have become an important food source.

This is in addition to the consumption of wild ponies, which "has grown by 96% since the '70s, if we look at the period from April to November, and has increased five times over if we look at it from December to March," according to Lagos, who emphasises that in this western part of Galicia wild ponies now constitute the wolf's primary source of prey, just like the roe deer do in the mountains to the east.

Improving coexistence with the wolf

But although sheep and goat stock are no longer as important to the wolf's diet throughout Galicia, researchers stress that cattle consumption has increased - despite their numbers having reduced by 37%. "It has been an increase of damage in cattle farming, perhaps due to new management methods rendering cattle more vulnerable to wolf attacks," Bárcena suggests.

The scientists agree that this state of affairs makes it more difficult for wolves and human beings to coexist, and has a negative impact on the conservation of this predator. For this reason, certain environmental management measures have been proposed, to ensure that the populations of roe deer and wild ponies increase.

"Habitat restoration work will also be needed in order to provide the wolves with a diverse and plentiful source of wild prey, which is essential if this canine population is to survive natural and artificial changes to its habitat, and if conflicts with livestock are to be reduced," the authors sum up.

According to Bárcena and Lagos, one further measure could also be taken: animal carcasses will not need to be removed. "This should be a fairly flexible regulation, which allows farmers with large ranches in remote areas to leave ruminant carcasses out in the countryside, and it seems more logical than disposing of them in rubbish tips. But this measure must first be properly assessed," they conclude.

Black bears in Yosemite forage primarily on plants and nuts

Black bears in Yosemite National Park that don't seek out human foods subsist primarily on plants and nuts, according to a study conducted by biologists at UC San Diego who also found that ants and other sources of animal protein, such as mule deer, make up only a small fraction of the bears' annual diet.

Their study, published in this week's early online edition of the journal Methods in Ecology and Evolution, might surprise bear ecologists and conservationists who had long assumed that black bears in the Sierra Nevada rely on lots of protein from ants and other insects because their remains are frequently found in bear feces. Instead, the researchers believe that bears likely eat ants for nutrient balance.

Rather than relying on indigestible foods found in bear feces for information about the importance of digestible bear foods, the UC San Diego ecologists looked at the digestible foods that were used to produce bear tissue. They accomplished this by measuring the abundances of carbon and nitrogen isotopes found in different species of plants and animals, and used a statistical approach to relate them to the carbon and nitrogen isotopes measured in bear hair. This allowed the scientists to quantify what the bears ate, then assimilated into their hair. 

The scientists also applied the same technique to Norway rats in Alaska's Aleutian Islands and determined that this invasive species subsisted largely on terrestrial plants and seasonal pulses of marine amphipods, rather than marine birds as had been long assumed. 

"Rats tend to dominate the habitats they invade on islands, killing much of the native fauna, especially birds, which is a serious conservation issue," said Carolyn Kurle, an assistant professor of biology at UC San Diego who conducted the study with Jack Hopkins, a postdoctoral fellow. "Using stable isotopes, we confirmed that marine birds have been extirpated to such levels on the islands where we worked that rats don't eat them anymore." 

"Both rats and black bears are omnivores with complex diets consisting of both plants and animals," said Hopkins. "To our knowledge, no study before this has accurately estimated the relative importance of plants and animals to the diets of these omnivore populations."

Hopkins said he and Kurle found in their study that plants and acorns are black bears' primary food sources in Yosemite. "We also learned that female bears foraged for high-fat acorns and pine nuts more heavily than males, suggesting that females likely need these seeds for reproduction. This could be a real problem for Sierra black bears in the future if blister rust continues to kill sugar pines and sudden oak death moves in from the coast."

Besides resolving the issue of what black bears and Norway rats actually use for growth and function, the scientists said a major goal of their study was to demonstrate how the use of stable isotopes derived from animal tissues and their prey could be used to quantify the resource use of other omnivores with complex diets.

"Ecologists currently focus too much attention on measuring the variation of isotope data for consumers and their prey and not enough attention on quantifying the interactions of consumers and their prey using isotope data," Hopkins explained. "Measuring such interactions and their relative strengths can help us understand the impacts animals have on their environment." 

Over the past two decades, black bears in Yosemite were involved in more than 12,000 reported incidents within the national park, injuring nearly 50 people and causing $3.7 million worth of property damage. In response to these problems, Congress has appropriated over $8 million since 1999 to mitigate human-bear conflicts in Yosemite.

Those efforts appear to be working. In a study published last year in the journal Frontiers in Ecology and the Environment, Hopkins and other scientists measured the stable isotopes of carbon and nitrogen in the hair and bone of Yosemite bears over the past century and found that since 1999, the proportion of human-derived food in bear diets has dramatically declined.

"Yosemite bears currently consume human foods in a similar proportion as they did in the early 1900s," said Hopkins. "This suggests a notable management achievement in the park, considering that thousands of people visited Yosemite annually in the early 1900s, while about four million people visit each year today."

Recovering predators create new wildlife management challenges

The protection and resurgence of major predators such as seals, sea lions and wolves has created new challenges for wildlife managers, including rising conflicts with people, other predators and, in some cases, risks to imperiled species such as endangered salmon and steelhead, a new research paper finds.

The study by scientists from NOAA Fisheries' Northwest Fisheries Science Center and the University of Washington examines recovering predator populations along the West Coast of the United States and in the Greater Yellowstone ecosystem, and the conflicts surrounding them. The study was published today in the journal Conservation Letters.

In the Pacific Northwest, for example, California sea lions that have increased under the Marine Mammal Protection Act have increasingly preyed on endangered salmon. Wolves reintroduced to Yellowstone in 1995 have since cut into elk herds, reducing human hunting opportunities.

"Increases in predators can be seen as successful in terms of efforts to recover depleted species, but may come at a cost to other recovery efforts or harvest of the predators' prey," said Eric Ward, a NOAA Fisheries biologist and coauthor of the paper.

The scientists describe three types of conflicts that can emerge as predators rebound under the protection of the Endangered Species Act and Marine Mammal Protection Act:

• Increased competition with humans for the same prey. For instance, sea lions eating fish also pursued by anglers and wolves preying on livestock and reducing elk numbers.
• Predators consuming protected or at-risk prey species, such as sea lions eating salmon and grizzlies consuming Yellowstone cutthroat trout.
• Protected predators competing with each other for prey. For example, sea lions consuming the same fish as killer whales, with wolves and grizzly bears also preying on the same species.

Pacific Northwest waters include many such conflicts, largely because many top predators such as sea lions, elephant seals and several whales are increasing in number and prey upon salmon, steelhead, rockfish and other fish protected by the Endangered Species Act.

Conservation conflicts have also emerged elsewhere: On California's San Clemente Island, a threatened island fox species preys on an endangered shrike, while protected golden eagles prey on both the fox and the shrike. Also in the Pacific Northwest, protected barred owls are moving into forest habitat long important to threatened spotted owls and double-crested cormorants, like sea lions, have been targeted for culling to reduce predation on Columbia River salmon.

The scientists call for improved monitoring and modeling to better anticipate interactions between predators and prey, and assess whether steps to manage predators may be warranted. Where conflicts continue, the scientists suggest developing multi-species recovery plans that consider the tradeoffs between increasing predators and other protected species.

"Predators such as bears, wolves and whales are charismatic creatures often seen as bellwethers of ecosystem health," said Kristin Marshall, a postdoctoral researcher at NOAA Fisheries who completed graduate research in Yellowstone and lead author of the paper. "We're fortunate to have places such as Yellowstone and the Northeast Pacific where they can recover, but in protecting one species you have to be thinking ahead to account for cascading effects that may impact other species too."

The ESA and MMPA do recognize larger ecosystem needs. For instance, the first purpose of the ESA is "to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved," and the MMPA seeks to "maintain the health and stability of the marine ecosystem." Both NOAA Fisheries and public land managers in the Yellowstone region are increasingly pursuing ecosystem-based management with those goals in mind. Research has also found ecological benefits from the reintroduction of wolves in Yellowstone.

Both the ESA and MMPA also provide safety valves by allowing limited control of recovering predators to manage their impacts under certain circumstances.

NOAA Fisheries has authorized states under the MMPA to remove sea lions known to be preying on endangered salmon, for instance. An "experimental" designation under the ESA allowed for removal of wolves that attacked livestock, although wolves are no longer listed as endangered in Montana and Idaho and are now subject to hunting.

But the scientists note that resolving conflicts by culling predators may itself have unintended consequences and will face public and legal opposition that may limit management options.

"Thirty years ago scientists predicted that increases in predator populations would cause more of these conflicts to emerge," Ward said. "We've largely seen these predictions come true, and there's no indication of these conflicts decreasing."

Down to 3 wolves on Isle Royale

CREDIT: ROLF PETERSON

Only three wolves seem to remain in Isle Royale National Park. Researchers from Michigan Technological University observed the wolves during their annual Winter Study, and the lone group, at an unprecedented low, is a sharp decline from nine wolves observed last winter.

The study's report, released today, marks the project's 57th year of observing wolves and moose in Isle Royale. It is the longest running predator-prey study in the world. This year, along with the three resident wolves, scientists estimated 1,250 moose on the island and observed two visiting wolves, which came and then left across an ice bridge to the mainland. This growing gap between the predator and prey populations is a trend that Michigan Tech researchers have tracked over the past four years.

"It's not the presence of wolves that matters so much, it's whether wolves are performing their ecological function," says John Vucetich, an associate professor of wildlife ecology who leads the study along with Rolf Peterson, a research professor at Michigan Tech.

Last April, the Isle Royale National Park released a statement concerning wolf intervention options. Part of the statement reads: "There is still a chance of nature replenishing the gene pool as wolves are able to move to and from the island when ice bridges form."

But with only three wolves remaining, Vucetich says, "There is now a good chance that it is too late to conduct genetic rescue." He also points out that one of the Isle Royale wolves left on an ice bridge last winter, and this winter, two wolves visited the island and promptly traveled back over the ice bridge.

Wolf Genetics

To understand Isle Royale wolves, you have to understand their genetics. Inbreeding has greatly impacted the packs over the past half century, which is clear with the three remaining wolves.

The group is most likely made up of two adults and one nine-month-old pup, possibly the adult pair's offspring. But unlike its pack mates, the pup does not appear healthy. It has a constricted waistline, hunched posture and seems to have a deformed tail, the researchers said.

"Those observations suggest that the pup is not well off," Vucetich says, noting that on the last day of the study, Peterson had found the two adult wolves, but not the pup. "It would not be surprising if the pup was dead a year from today."

Even if the pup were healthy, it would not necessarily be a promising sign. In the case of wolves, three is not a crowd. Such low numbers make the population's natural recovery unlikely. The wolves' numbers started plummeting in 2009, declining by 88 percent from 24 to 3 wolves, which Vucetich and Peterson think is a result of inbreeding. All geneticists who have studied the current situation agree that recovery is unlikely without new genetic material.

With that in mind, even if the surviving adults are a mating pair, their offspring probably would not fair well. While the researchers are waiting on genetic tests to confirm the wolves' identities and which pack they came from, their best guess is that they are the alpha pair from West Pack. And, as a mating pair, neither is likely to be interested in other potential mates introduced for genetic rescue.

Visiting Wolves

Looking for wolves in winter is challenging, Vucetich says, describing how he spends hours looking out a small plane window, searching for tracks or subtle signs. One day this winter, the work paid off in an unexpected way.

"I could see these two wolves, they were on top of a ridge, curled up in tight little balls," Vucetich says, explaining that the wolves were asleep. "And wolves can sleep for quite some time, so we circled for a bit and decided to come back later."

Of course, when Vucetich and the pilot came back, the wolves had trotted off. But based on the tracks and the geography of Isle Royale, Vucetich says it was easy to guess the wolves' preferred travel route. They found the canines skirting the shoreline soon after.

One wolf appeared light-colored, which is uncharacteristic of Isle Royale wolves, and the other was radio collared. They were visitors who had crossed an ice bridge from the US-Canadian mainland, where the Grand Portage Band of Lake Superior Chippewa had collared the wolf.

But they didn't stay long. Within the week, the wolves left, traveling back across the ice bridge.

"Everyone wants to know: What does this mean?" Vucetich asks. The answer is unclear, despite the fact that visiting wolves raise hopes for saving the population. Vucetich and Peterson write in their report that even "if the visiting wolves had been aware of the presence of Isle Royale wolves, it is far from certain that genetic rescue would have occurred."

The remaining two options, then, are to reintroduce wolves to the island or do nothing and see what happens naturally.

"One must use the word, 'naturally', carefully these days," Peterson advises. "The human imprint is written all over the dynamics of this wolf population in recent decades".

A case in point, he says, is the downward trend in the frequency of ice bridges in winter, which formerly allowed wolves with new genetic material to make their own way to Isle Royale.

Booming Moose Population

Along with wolves, the other iconic animals of Isle Royale are moose. And unlike their canine predators, and in spite of several harsh winters, the moose population has been growing annually at 22 percent for each of the past four years.

"If that was money in the bank, you'd get rich in a hurry," Vucetich says. "Soon we'll be moose rich."

While iconic, a proliferation of moose could actually be harmful and, if this trend continues, the population could reach past heights like in 1996.

"At that time the moose population had considerable impact on forest vegetation," Vucetich and Peterson write in the Winter Study annual report. "Concerns remain that the upcoming increase in moose abundance will result in long-term damage to the health of Isle Royale's vegetative community."

The balance of predator-prey on Isle Royale has clearly tipped. The question remains what actions humans will or will not take to influence that scale.

###

The annual report is available at: www.isleroyalewolf.org