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Report on the Clark’s Fork elk herd

It snowed about 4″ here last night but I braved the drive into town early in order to hear Arthur Middleton’s talk at the Buffalo Bill Museum.  Arthur is the PhD student that’s in charge of the study on why the Sunlight elk herd has such low calf/cow ratios.  He’s been working up here in the field for 3 years, and now he expects to crunch all the data for another 3.  But his preliminary findings were what he wanted to report today to the public.

First off, I’ve seen his interns up here for the past two years and gotten to know them and Arthur.  I can’t say enough about how focused, diligent and hardworking these students are.  Up at dawn in the dead of winter to observe elk in the freezing cold.  As Arthur put it today, they had 4 behaviors that were noted:  feeding, bedding, vigilant, and running.  That’s about all the elk did, day after day.

Arthur did a great job of presenting all this info to the public in lay person’s terms.  He used slides and began step by step explaining some of the biology necessary to understand the complexity.  Simply put, there are many factors to consider, and I do remember at last years’ good-bye party for the interns listening to Arthur thinking all the factors through.  Here’s my summary of Arthurs’ points and I hope I’m doing justice to it all.

1.  First there are two herds that he studied, one migratory (Sunlight herd migrates here in winter and to the Park in the spring/summer/fall); and one non-migratory which is down north of Cody.  By looking at data from a lot of years ago, the elk have changed their patterns.  There used to be no non-migratory herds around here.  Migration, as Arthur pointed out, is a fairly fixed behavior taught by cow to calf, so it takes many years to make a change.  Arthur explained the advantages of migration, mainly better food quality as the elk follow the new grasses up as the snow melts.  There might be some predation advantages too as the predators den in the spring and stay put for a while as the elk move higher up.

Elk from the trail camera

2. Arthur explained how lactation takes a lot of energy from the mother (as all of us mothers know!).  Basically, non-lactating elk have 50 pounds more fat on them than those that lactate.  While the normal pregnancy rates for elk is 90% (and the NON-migrating herd is at that bar), the Sunlight (migrating) herd is at only about 60%.  The premier finding of this study was that the Sunlight herd cows are only getting pregnant every other year.  By doing that, they save energy vis a vis body fat that helps them through the winter.

3.   Displaying a slide of the rainfall patterns over the last hundred years, and comparing that with satellite data that looks at greening rates (especially in the months of June/July during lactation), we could see that this area has been in a severe drought, as well as compressed warming trends (i.e. shorter winters).  A photo of the high mountain pass between Sunlight and Yellowstone in June showed not as much green as should be expected.

4.  Another interesting find was behavior, what the interns were watching during those months they were here.  The vigilant behavior time was the same for the non-migratory and the migratory.  But where they differed was that the non-migratory herd spent more time bedding while the migratory herd spent more time feeding.  The nutritional quality of the migrators just wasn’t as good.  Factors governing the non-migratory herds were irrigated pastures and intentional low grade fires set to improve grazing in areas where cattle are.  The migratory Sunlight herd goes up through wild and high country where natural fires and rainfall determine feed quality.

More elk

5.  Lastly, looking at predation, Arthur showed a chart from research in Yellowstone pre -wolves on calf predation.  Predation was looked at by bears (main predator of calves), coyotes, cougars, natural causes, and survival rate.    He compared that to a more recent chart that included wolves.  Interestingly enough, wolves were almost about the same as the coyotes in the first slide but the bear predation had increased 3 fold. Lots more bears are in the Park since the 80’s.

This grizzly spent hours upturning Bison paddies for insects underneath

Although Arthur has more data to analyze, it seems obvious that the main factor that is affecting this herds’ decrease in cow/calf ratio is quality of feed.  These elk, smartly enough, are compensating for the nutritional loss by having calves every other year, instead of every year.  Add to that the increased predation on calves by bears in the park, with the new factor of wolves predating at the same rate as coyotes approximately, and you pretty much get your 30% drop.

Bull and cow mating in Yellowstone

One other comment Arthur made was that most of the migratory herds are doing well in Wyoming.  Sunlight as well as one other herd stood out as extremely low on a comparison chart and that was why this study was conducted.  Why this herd suffers more from drought than other herds–you’d have to look at each herd individually.

After the talk I went to the local hairdresser to make an appointment for next week.  As I was waiting at the counter, I noticed a large poster ready to put up, advertising the ‘Wolf Rally’ in Cody on May 22 by hunters, like the one in Jackson several weeks ago.  These guys are blaming wolves for all their woes and want the Wyoming delisting plan enacted which would give the wolf  predator status all over the state (meaning you can shoot on sight).  On the tag line of the poster there was an invitation to ‘Come and learn the science of what’s happening with the wolves and elk’.  Somehow I don’t think so.

Nature is a beautiful complexity that takes much time and pondering to put some of the pieces together that Man can understand.  What I learned from so many of my biology classes is that things are just not as simple as you think.  I watched Arthur over these last several years thinking through so many pieces of this puzzle in a questioning way, trying to piece parts together.   Its much easier to have an emotional opinion, play the game of scapegoat, and rally around a cause.

2 Responses

  1. […] herds in the Greater Yellowstone Ecosystem.  You can read the controversial results of that study here on my blog, and here on the […]


  2. […] although these elk have been thoroughly studied, they still contain many mysteries.  For instance, for the past seven years that I’ve lived […]


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