Declining Deer Population: Blame the Mountain Lions?

This is the time of year with Spring in full bloom that here in Colorado, we are likely to see more wildlife. It has been my good fortune to see a fair amount these past few weeks – beaver (which I had never seen until now), muskrat, avocets and then a few days ago a herd of seven mule deer grazing on the side of a slope above Clear Creek just beyond the entrance to Clear Creek Canyon. We had been hiking. Nancy went on a bit; as usual, I waited behind and took a seat on an inviting rock, looked up; there were all seven of them making their way down along a stream bed not far from me.

Alert, the deer were typically nervous, their ears going back and forth. Apparently deciding that in the end I was not much of a threat, they inched closer until they were no more than a hundred feet away, maybe closer. Common as deer are, it is still a great thrill for a kid (well, I’m 71 now) from Brooklyn to be in the presence of a deer herd wandering freely in the Colorado mountains. I don’t remember seeing them in Flatbush where I was born, not even in the wilds of Prospect Park.

Unlike the other wildlife described above, deer are quite common – not just in Colorado, but nationwide. It is not unusual to see small herds in the mountains either in the early morning or towards dusk. In some places, like Boulder, they are something between house pets and nuisances, enjoying garden produce sometimes more than the people who are raising the crops. On his farm in Lyons, I remember that my father-in-law would scare them away by firing blanks at them with is rifle. It worked pretty well for a short while and then they returned.

National Trends

Nationwide, the useful and informative website “Deer Friendly” provides a good deal of insights into both national and local trends.

Both here in Colorado and nationally deer populations are in decline – one might say plummeting. Nationally the trend is long term. “Deer Friendly” reports that from 2000 to 2014 deer population have decreased from close to around 7,350,000 to 5,960,000, a drop of nearly 19%. It must be noted that these are approximate figures given that the ways in which deer are counted vary in different states, still the trend appears pretty clear: deer populations are dropping. These numbers fail to note that a hundred years ago, the deer population – like that of so much other wild life – was almost hunted to extinction. Looking at the figures over the longer term, this is quite a come back. So it would be more accurate to say, that there has been something of a deer revival which peaked – like the stock market – around 2000 and has been unstable ever since. (Wonder if there is some connection? – but for the sake of sanity – let’s not go there, at least not yet.)

Following the national trends, the Colorado deer population is also in decline these past 15 years. According to Colorado Parks and Wildlife (CPW), reported in The Denver Post, in August, 2014 “CPW’s most recent population estimates continue to show a significant statewide decline in mule deer, down by 36% to 390,000 in 2013 from 614,000 in 2005. The national decline of 19% noted above covers a 15 year period; Colorado’s mule deer decline of 36% is covering only an eight year period suggesting that deer populations in the state are dropping at nearly double the national average.

What’s the deal? Why the decline in the numbers?

Not to be cynical but, the big deal, frankly, is that hunting is a billion dollar business in Colorado and the concern over deer population decline involves hit on the state’s prosperity.

“Deer Friendly” cites three factors in the numbers’ shrinkage: “food supply, predation and energy development.” Explaining the decline at a 2014 conference made up mostly of Colorado mule deer hunters, Brad Weinmeister, a CPW biologist put it this way:

“We are all guilty of it [the decline in the deer population]. The last 20 to 20 years there has been a lot of growth in homes in th country with the new roads, driveways, dogs, horse pastures and traffic. It takes away from habitat and puts stress on the animal.”

While there is much truth in Weinmeister’s statement, it is a bit of a stretch to say that “we are all guilty.” Is that environmental version of the Calvinist idea that we’re all sinners? No we are not all guilty…and there are some well known suspects in fact who are frankly far more guilty than others. Don’t blame the hunters either. Besides the fact that the numbers of hunters culling deer herds provide a necessary check on a deer population, deer hunters are, in their overwhelming majority quite sensitive to careful wildlife management – if only to maintain the sport they so love.

No, the decline has much more to do with the development epidemic that has touched every corner of the state and is most intensive in the mountains. Between ski centers, home building, the kind of mining that has eroded much land and poisoned no small amount of Colorado’s water supply, wild life have had a pretty hard time of it. Add to it now the fracking frenzy  and it is surprising that the deer decline isn’t greater.

But, as the state is unlikely to do next to nothing (no – it will do nothing at all)  to put the breaks on Colorado’s development mania, state authorities have looked for another  explanation for mule deer decline and have come up with a somewhat less than brilliant solution to boost the deer herds: cut the mountain lion population! I guess it couldn’t be called “blaming the victim” but maybe it could be called “blaming the least guilty suspect.”

So mountain lions now are the fall guys for developers and real estate companies.

Last August, the Colorado Springs Gazette ran a story about how Colorado Parks and Wildlife hopes to increase deer populations in four nearby game management units as they are called north of the Arkansas River, between Salida and Canon City by allowing hunters to kill more mountain lions that pray on deer. It would permit hunters to increase the “mountain lion harvest” from a limit of 24 to 25 cats annually with a goal of doubling the area’s deer population.

The same article notes:

“The plan has drawn the ire of animal rights and conservation groups, who say that oil and gas development, habitat loss, disease and competition from elk and livestock are bigger threats to mule deer than any of their predators.”

As my daughter’s used to say when I’d say something either obvious or downright dumb…duhhhh!

Another factor is the prevalence of infectious brain disease, or chronic wasting disease as it is also called, that has been killing deer as well as elk and moose in Colorado – and in 22 other states and two Canadian provinces. Just how much chronic wasting disease has contributed to Colorado deer decline is difficult to ascertain, in part because the linkage between that cattle-infected and deer infected varieties while genetically very close is still open to question.

Nor have their been studies (to my knowledge) that would provide scientific evidence explaining the extent to which the disease is linked to population decline. Still it is striking that the parts of Colorado that have the most intensive number and size of cattle feedlots are also those in which the deer population have chronic wasting disease in epic proportions. So it can be said that cattle feedlots and mule deer chronic wasting disease seem to go together “like a horse and carriage.”And as the condition seems to have the ability to mutate and effect one species after another, the eerie possibility of some variation of chronic wasting disease “jumping” from deer and elk to their main predators in these parts – mountain lions. To date, there has been no evidence of such an outbreak among mountain lions, but it wouldn’t be a great surprise should it happen – if it hasn’t already. So Colorado mountain lions are getting it from both sides – from hunters and from the deer and elk they largely depend on for survival.

And as the condition seems to have the ability to mutate and effect one species after another, the eerie possibility of some variation of chronic wasting disease “jumping” from deer and elk to their main predators in these parts – mountain lions. To date, there has been no evidence of such an outbreak among mountain lions, but it wouldn’t be a great surprise should it happen – if it hasn’t already. So Colorado mountain lions are getting it from both sides – from hunters and from the deer and elk they largely depend on for survival.

The condition leads to “the characteristic spongy degeneration of the brain, leading to emaciation, abnormal behavior, loss of bodily functions and death. First identified in captive mule deer populations in a Colorado mule deer facility in 1967, the disease has reached endemic proportions in “a large swath of land in northeastern Colorado and southeastern Wyoming. First identified in captive mule deer populations in a Colorado mule deer facility in 1967, the disease has reached endemic proportions in “a large swath of land in northeastern Colorado and southeastern Wyoming.” There was also a 2008 case of contaminated elk meat sold at a farmers’ market in Longmont, Colorado that was found to come from a captive elk population infected with chronic wasting disease. How long will it be before the first reports of mountain lions being stricken too?

Is it more than a coincidence that this condition is especially widespread in that part of Colorado – the northeast – also known for its large cattle ranches and feedlots? Closely related forms of the condition have jumped from cattle to humans through the food supply; could the condition not have also mutated to effect genetically related (to cattle) deer, elk and moose?

According to the Colorado Cattlemen’s Association, Colorado feeds more than 2.3 million cattle annually, raised on 11,600 farms and 206 feedlots. Of Colorado’s 35,600 farms in 2013, 56.1% raised livestock (cattle and sheep primarily). Livestock are slaughtered in 24 USDA approved slaughter lots. Cash receipts for Colorado livestock and products total more than $3.7 billion, of which more than 75 percent of cash receipts come from cattle and calves. It is shipped worldwide and has been since the 1870s when a cattle baron named John Wesley Iliff shipped tens of thousands of head of cattle to France during the 1870-1871 Franco-Prussian war. That is a prodigious amount of meat that iis processed here, most of it on the state’s northeast quadrant where 150 years prior, the deer and the antelope played and buffalo roamed.

Chronic wasting disease that brings down deer, elk and moose is related to a group of fatal diseases referred to as “transmissible spongiform encephalopathy (TSE). The group includes “mad cow disease” (bovine spongiform encephalopahty, or BSE) in cattle, scrapie in sheep and variant Creutzfeldt-Jakob disease in human, which, according to the World Health Organization, has been “strongly linked” to eating beef products contaminated with central nervous system tissue, such as spinal cord and brain from cows infected with mad cow disease.


I have seen one of these magnificent cats in my 47 years in the state; it was down by Crested Butte on a hike along what is called Cement Creek. It was walking along a ledge on the other side of the creek. I was with Nancy and daughter Molly, who was a baby, my sister and her then-husband, Hubby and their son, Benji. It walked parallel to us for about 20 feet and then, thankfully disappeared into the brush. No one one else in the party saw it and when I told them that I did I am not certain that they believed me. I’ve also looked for them on several occasions in the mountains above Boulder but have never seen another.

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Rob Prince lives in Colorado.

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