Warning for Wyoming hikers as 'monstrous' animals eating 20,000 calories a day are on the prowl

Hunters on the Great Plains may find they're no longer top of the food chain as the approach of winter sends nature's predators into a frenzy.

Hundreds of hairy omnivores face a life-or-death struggle to fatten up before they spend months in hibernation and they are not about to let anyone stand in their way.

Key food sources are in short supply this year, naturalists have warned, sending the bears ever closer to human populations and heightening the risk of aggression to any hiker or hunter who strays across their path.

'They can eat pretty much anything,' said retired federal ecologist Chuck Neal.

'It's not a question of what, but how much they get their jaws around.'

The nation's population of Brown and Grizzly Bears are currently enduring a state of 'hyperphagia' - an insatiable appetite that kicks in ahead of their winter hibernation.

They have to consume around 20,000 calories a day – and they're not fussy about where they get them.

'They can actually consume more than that, depending on the food source,' Neal told the Cowboy State Daily.

'They can put on 200 to 300 pounds from July to November. It's their biology. It's what they evolved to do in preparation for the winter sleep.'

But 10 people are known to have been killed in bear attacks across the US in the last five years – half of them during the winter feeding season.

'The whitebark pine has been decimated, primarily by outbreaks of mountain pine beetles,' Neal said. 'But they're very adaptable, so they've had to switch to other foods.'

Georgia hunter Landon Clement said he felt like he had been 'hit by a train' when he was tackled by a hangry Grizzly in Wyoming's Upper Green River Basin on Thursday.

The 31-year-old from, Blue Ridge was archery hunting with a friend when he saw a mother and two cubs feeding in the woods.

'When those bears cut down that trail and veered toward me, I knew I was probably going to have an issue,' he said.

'I was still backed up against a rock, and when I realized that they were coming my way, I just backed up even further against that rock, I was practically glued to it.'

The bears stopped in their tracks when they spotted the hunter before the mother decided to attack.

'She just leaped. She just charged right at me with her mouth wide open,' Clement said.

'I've never seen anything move that fast, she covered that 10-12 yards in less than a second.'

The hunter tried to fire his semiautomatic pistol at it only to find that its mechanism had jammed.

'It bit into my left thigh, and it would not let go,' he explained. 'It just bit into my thigh and starting shaking its head.

'As the bear was still clamped onto my leg, I was finally able to look down and see that my gun was jammed.

'Once I cleared the jam, I put the gun as close to its head as I could and shot a couple of more times. It let go and rolled off me. I knew that I had killed that bear.'

A disabled Army vet nearly bled to death after being attacked by another momma bear in Wyoming's Grand Teton National Park earlier this year.

Shayne Patrick Burke, 35, from Massachusetts had travelled to the reserve to take photographs when he was attacked on Signal Mountain.

He was only saved when he shoved a can of bear spray in the animal's jaws and it bit down, causing the container to explode.

There are thought to be more than 1,000 Grizzlies and up to 650 Black Bears in Wyoming all of which are currently feeding for up to 22 hours a day.

And their numbers have been boosted by animals straying in from Yellowstone National Park.

'That's when we often see bears in lower elevations,' Neal said.

'They may show up in a cornfield outside of Powell or the Shoshone River bottoms eating silver buffaloberries. 

'They're searching for all the calories they can possibly pack on, and sometimes that takes them onto the periphery of their currently occupied range.'

And with their feeding season coinciding with hunting season, many hope to win a share of the spoils and the 'gut piles' hunters leave when disemboweling their kills.

'Hunters have a special obligation to be vigilant because they're putting dinner on the ground,' Neal said.

'Bears are seeking out gut piles. That is highly nutritious food, but it also places bears in proximity to hunting groups and men with guns.

'The mortality rate for bears has gone up due to run-ins between man and beast over gut piles.'

The clock starts ticking for the bears as soon as the days start shortening in July, and they will cover as much ground as they need to before retiring for the winter in November.

'The point to remember is that Wyoming was always an occupied range for bears,' Neal said.

'The bears have been pushed back into the Yellowstone country over the last century or so due to the expansion of human populations, and they are simply trying to recolonize what they always occupied.

'The possibility of more confrontations between man and beast do exist as they're looking for more calories during hyperphagia.'