Presence of wolves helps survival of pronghorn fawn, normally a major prey item for coyotes-
Wolves have a complicated relationship to their prey and to competing carnivores and omnivores such as bears. Simple statements such as every animal a wolf kills is one less for a hunter are fantasy. In reality wolves can directly or indirectly cause the populations of their prey to drop, remain steady or even increase as they exert their many effects on the environment and the environment influences their population size too (witness the big natural decline in the Yellowstone Park wolf population). The effects of wolves can also change over time in the same area depending on external events such as forest fires that influence their prey and wolves’ competitors.
Nevertheless, generalizations are possible and one of the more interesting ones is the tendency of wolves to benefit pronghorn antelope populations in places where pronghorn numbers are being suppressed by heavy coyote predation on the tiny pronghorn fawn. Neither wolves nor coyotes have any effect on adult pronghorn because they can’t catch them except in very rare circumstances.
First noticed at least a decade ago, there is considerable evidence that wolves are indirectly leading to an increase in pronghorn populations in both Yellowstone and Grand Teton National Parks.
Patrick Dawson has a lengthy article on wolves, coyotes, and pronghorn in WyoFile. Do Wolves help Pronghorn? Yellowstone Pronghorn find sanctuary in the Shadow of the Wolf.
Comments
From the article:
++Dr. Kim Berger, lead author of the study (says), “But in this case, wolves are so much bigger than coyotes that it doesn’t make sense for them to waste time searching for pronghorn fawns. It would be like trying to feed an entire family on a single Big Mac.”++
Now if that were a completely true statement wolves wouldn’t eat rodents and rabbits during the summer months. Hope she wasn’t taken out of context, but it is kind of a stupid statement.
To be fair, the quote says, “…it doesn’t make sense for them to waste time searching for pronghorn fawns” (emphasis added). There is a difference between eating prey one encounters and actively searching for that prey item. In any case, the smaller the prey item, the more dense their population would need to be to make it worthwhile for a carnivore to actively hunt/search for them.
But, wouldn’t the same logic apply to coyotes – wasting time looking for pronhorn fawns? Except for the fact that there are more of them and they are smaller (lower nutritional needs by virtue of size), the question is still valid. It would seem an individual coyote might have the same success rate as an individual wolf, whether by chance, or seeking out fawns.
Also seems, odorless as fawns might be, mama (not so odorless and visible) might be nearby, and being a smart and adaptable animal, wolves might figure that out over time. Wolves, coyotes and bears are predators of opportunity and will repeat behavior if it works for them.
Whether time spent foraging for a food item is “wasted” depends upon the density of the food item and its size (energy value) relative to the size of the forager. For a coyote, which is ~1/4 the size of a wolf, the value of any given fawn is much greater (~4x) than for a wolf. This difference may be enough to make coyotes preferentially target pronghorn fawns, while wolves concentrate efforts elsewhere.
Pronghorn fawn birth weight is less than 10 pounds, about the same as a whitetail deer, and maybe a tad less than a mule deer. Both species can have twins, but maybe pronghorn more often.
The pronghorn prey density and size remain the same for both coyote and wolf. And, as you say, the “reward” for finding may be greater for the coyote relative to its caloric needs. Obviously higher coyote density means more fawns will be found. Wolves regularly eat deer fawns, so why not pronghorn fawns when available as do coyotes? Not enough detail here, IMHO.
Here is what I find interesting. The article also mentions other research concluding that where pronghorn and wolves are now, the pronghorn are choosing to birth in the timber (where there is better ability to hide from some predator eyes), thus also contributing to boosted fawn survival.
Query, if wolves are not perceived as a risk to depredation by wolves, why would mama pronghorns-to-be choose to go to the timber to avoid them? Think they are just a big coyote?
And, by the way, I am not suggesting that wolf presence (and by association coyote reduction, and changed pronghorn behavior) is not beneficial to increased survival rates in pronghorn fawns. This is great news.
The semantics is interesting here, with the terms “wolves helping” as the article uses, and the title of this thread which says “wolves protecting.”
Would a more honest description of the relationship, be in the saying, “The enemy of my enemy is my friend (for now anyway)?”
With fewer coyotes and maybe more wolves in this area will this relationship change? Higher survival rate of fawns may mean larger pronghorn population, which means more young of the year, which could mean higher density in some places (predator population follows prey mostly). Will wolves then have high enough density in the timber or in the historic fawning areas to make it worth their while, if it is not already? Lots to ponder.
“Would a more honest description of the relationship, be in the saying, “The enemy of my enemy is my friend (for now anyway)?””
LOL…absolutely! I think the fundamental question (that I don’t think was addressed) is: Does pronghorn fawn survival benefit from wolves because of differences in foraging behavior (between wolves and coyotes), or is it a function of overall carnivore density (wolves have much lower densities than coyotes, so by killing coyotes fewer fawns are encountered)? Of course, it also could be a combination of the two. However, I also think it is safe to say that wolves are generally targeting elk, whereas coyotes are targeting pronghorn; shouldn’t we expect coyotes to be more successful?
FYI: Just read another paper that found that indicated that rodent numbers are actually higher around (within 3 KM of) wolf den sites than in more distant sites. The authors suggest higher coyote predation in more distant sites accounts for the difference.
Miller et al. (2012) Can. J. Zool. 90: 70-78,
Since there are more coyotes who occupy much smaller territories, statistically speaking, their odds of stumbling across a fawn would theoretically be higher.
That’s aside from assuming that one coyote and one wolf both have an equal chance at stumbling into a fawn.
I do wonder whether a well-fed wolf pack is less inclined to hunt opportunistically for small mammals, as opposed to coyotes who will rarely score meals large enough to preclude them from staying on constant alert for the next meal.
Additionally, growing wolf pups tend to consume more small prey than adults due to poor hunting skills. Big difference required for learning to detect hidden and nearly odorless pronghorn fawns verses plentiful small mammals (often close to dens and rendezvous sites).
One would certainly expect wolves to help pronghorn, but it’s interesting to me that the Northern Range pronghorn population has not grown since wolf-reintroduction and actually declined from 600 in 1990 to between 200 and 300 today. GTNP has seen the opposite effect since reintroduction, with a 50% increase. This difference would lead me to believe that other factors are at play and that the presence of wolves has only a marginal positive effect on pronghorn populations.
That difference is mostly habitat. Yellowstone national park, and especially the areas where you find pronghorn are open meadows and sage brush country. In areas outside of national parks those areas are heavily grazed on by heffers.
Sam Parks,
I will accept that your numbers are correct. I haven’t checked, but your point is important. There are always a number of factors that affect populations of pronghorn and other animals. The effect of wolves on pronghorn is always indirect. The direct effect of wolves is always to kill a pronghorn adult or fawn if an easy chance presents itself. The indirect effect of wolves does need to be teased out of the data, and it might not always be there. For example, what if the coyote population is low to begin with in an area?
As an aside, it seems like I recall that pronghorn populations had dwindled to only about a hundred by 1999. I need to look that up.
Sam Parks and Wilderness Guy,
A little research just now tells me that Yellowstone Park pronghorn populations are primarily limited by the amount food available to them. Wilderness Guy, you are right.
There were thousands of pronghorn in the Park at times of the year in 1872, but within 15 years their numbers were greatly reduced by direct human killing and plowing up their range just outside the Park.
When the U.S. army took over the Park they began to feed the pronghorn alfalfa hay and their numbers began to climb back, but in the 1930s the feeding was stopped and a great drought set in. The numbers crashed. While the population goes up and down today, there is not nearly enough range to support more than perhaps 300 on a long term basis.
Besides having a direct physical impact on coyotes, I wonder what the overall effect of wolves has been on the coyotes’ food availability? As the elk population grew rapidly from a bottom near the end of the elk reduction program (around when I arrived in Yellowstone in 1965) I noticed a substantial increase in coyote activity over time, becoming most noticeable when the elk population grew very large in the 1980s and 1990s, with substantial evident mortality, although more extensive in more severe winters. There was a large amount of carrion available on the northern range every winter during that period that the coyotes used. During those years, coyotes seemed very abundant and that is about when we started hearing that the pronghorn herd was in danger from coyote predation. Other species may also have been affected, because I remember one photography outing on the bench just north of the 45th parallel, when I saw about 40 bighorn ewes with only one very nervous looking lamb, and found remains of another lamb and saw numerous coyotes in the area including one pack of 7, which was more than anything I had seen before. So perhaps the coyote population was elevated, fueled in part by carrion availability, at about the time of the wolf introduction. There is probably a lot less elk carrion hitting the ground these days, but on the other hand it is likely more spread out (brought down by predation rather than nutritional stress and weather). I guess it comes down to how successful coyotes are in scavenging wolf kills? A couple of years ago in September, I observed two coyotes eating peacefully on a elk kill on Soda Butte Creek while two completely stuffed and indifferent wolves lay not far away.
I do remember seeing occasional pronghorns on places like Specimen Ridge, but they seem far more abundant in the Lamar now than I ever remember, even if the total park population is not up that much. They used to drop fawns in the Gardiner area . . . . I found a number of them hiding while walking around Stevens Creek and on the flats between the Gardiner and Yellowstone. So, that may be something that has changed if they are having more of the fawns out in the park. Of course, weather/range conditions related to drought could also be a factor in their recent distribution, as well as their abundance.
Thanks for your observations, Seak. I see more pronghorn in the Lamar Valley and adjacent areas too. I wish I knew the status of the northern range’s coyote population. It fell by 50% at first, but I have heard little since, but I’d bet someone like Dr. Robert Crabtree might have done some published research. Maybe a report is on line.
Ralph:
Coyote populations have since rebounded in Yellowstone.
Seak:
My understanding is that wolves leave less biomass (in the form of carcasses) for scavengers then when animals die via other means (3-4 times less, if memory serves). However, the fact that they make kills year round has the effect of “spacing out” carcass availability temporally.
I have also commented on a different forum, on the increasingly visible populations of pronghorns in Little America, certainly Lamar, and around North Entrance as well. As a side note, I’ve always wondered why we don’t see them in sage-laden Hayden, could someone comment on that?
In any case, the other animal that I believe has been affected by wolf re-introduction is the red fox. I didn’t see my first fox in Yellowstone until about 2006, now I always see one or more per trip. I suspect the apparent resurgence of foxes may be related to whatever impact wolves have had on coyotes, which are more important fox competitors than wolves, than any direct impact from the presence of the wolves.
This is just my hypothesis, I would value informed feedback on the matter.
Gal Yellowstone —
I lived at Mammoth from 1965-1975 and have returned often since. I also saw my first red fox in the park around Ice Box Canyon during my last visit in September 2010, and was wondering the same thing about the effect of wolves.
Gal Yellowstone,
Your theory about Yellowtone foxes is correct. Coyotes are to red foxes what gray wolves are to coyotes, and what red foxes are to smaller gray and kit foxes. The larger canid doesn’t just compete with and displace the smaller canid, it often kills it.
I used to only see red foxes where I live. Then coyotes showed up and before long the red foxes became scarce. Neither are native so I was glad to see more native gray foxes after the coyotes decreased the red fox population.
The answer might lie in following the Pronghorn migration routes. All animals do well in the summer months. Winter decides their fate and viability. Pronghorn used to migrate all the way down the Paradise Valley to the plains of the Yellowstone for winter, and thrived. They cannot do that these days because we humans fractured the range with fenced lots , highways, and domestic livestock.
In short, we walled off their nominal habitat at the time of year they needed it the most. Populations adjusted to those unfortunate circumstances
Gal Yellowstone – 20 years ago a red fox was a rare sighting (in my area of southwest Montana) you heard about them, but seldom saw them. Over the last 10 years or so, I see them often now. And coyotes? Use to see and hear them all the time, and now? Not so much.
I’m smack dab in the middle of cattle country so I don’t see or hear wolves too often either, unless its winter and they’ve taken a calf or even dare to look at cattle, while passing thru (WS addresses the situation quickly) so one does have to wonder how the dynamics have changed with other predators, when there’s even a hint of wolves around.
Alas, my wildlife viewing is limited to June (at least in most years) and to Yellowstone & the Tetons, so I can’t comment with much authority, but we certainly still see coyotes in the parks, especially in winter (same is true for wolves, easier to spot then too). Some years we see many coyotes, this year, only 3 or 4. Our bear sightings were low this year too but not for others there at the same time. The Gods of Wildlife Sighting were just not with us much on these two critters in 2012. It’s so hard to know what the bigger picture is.
Nancy the first red foxes that I ever saw were in the Big Hole Valley in 1966. I saw lots of them that summer.
Elk I don’t remember the exact year but there use to a fox farm about 1966 that went belly up and released the farm bred foxes into the wild. It was a disaster for the game bird population.
Elk – not just commenting from my own experience, had quite a few longtime locals say the same thing – red foxes were not often seen. The Big Hole Valley also seems to have a lot more wolves than other areas. Must be the water 🙂
It is always dangerous to drill down on one species behavior and drawn conclusions about an ecosystem, but intuitively it seems that coyotes are far more likely to prey on pronghorn calves than wolves are. So if wolves negatively impact the coyote population that should help Pronghorns
I understand Grizzlies eat a lot of elk calves. It is possible that if big males spend more time chasing wolves off of adult kills that might actually spare calves and help the elk population as a whole instead of hurting it. Unfortunately the weather seems to crowd out other factors so it’s hard to tell what’s really going on.
I don’t think we can ever understand the relationship of wolves to elk very well in any area where wolves and bears, especially grizzly bears live together.
This conclusion does not apply to pronghorn, of course.
Snaildarter is right about the weather. Yellowstone has been in a drought for most of the time since wolves were reintroduced there. Drought reduces biomass a lot. Yellowstone in total has less for all things to eat than a generation ago.