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Idaho surveys indicate no change in elk seasons

Chart shows elk ratio of calves per 100 cows in Idaho Panhandle game management units. (Idaho Fish and Game)
Chart shows elk ratio of calves per 100 cows in Idaho Panhandle game management units. (Idaho Fish and Game)

HUNTING -- Winter elk surveys are being hindered in the Idaho Panhandle by poor visibility and flying conditions. 

But Jim Hayden, Idaho Fish and Game Department regional wildlife manager, says he has enough information to at least predict there's little hope that elk calf survival has increased enough to improve hunting seasons that were scaled back last year.

Click continue reading to see Hayden's detailed update on the ratios of elk calves per 100 cows in Idaho Panhandle game management units.

This hasn’t been a great year for flying weather, and we’re still waiting on another 5 days or so of clear skies to get finished with our flying for elk information. We’ve got a pretty good handle on how well calves have fared this year in most of our units, but our “counts” (in key areas of Unit 4) are only about half done. I figured I’d start talking about our calf information anyhow.

The ratio of calves to cows gives us a lot of insight into an elk herd. It’s just straight-forward logic - if calf ratios are low, then we aren’t “recruiting” enough calves to replace the mortality on cows, and the herd goes down in numbers for the year. If they’re high, then there are more than enough calves to replace the mortality on cows, and the herd goes up. The cow mortality rate (percentage of cows dying from all causes) changes back and forth from year to year, and is different from unit to unit, so we have to generalize when we say we want to be at about 30 calves per 100 cows before we have much of a cow hunt.

A lot of things affect whether calf ratios are low or high for the year. For example, unlike deer, few yearlings elk (cows) breed, so the percentage of yearlings in the herd will affect the ratio of calves to cows.. Adult cow pregnancy rates affect the ratio of course; although it turns out these don’t change very much. Disease such as Brucellosis, (also known as contagious abortion disease) is present in Yellowstone and near elk feedlots in Wyoming, and can depress calf ratios. The largest influences though are probably predation and the annual energy budget (ability to gain enough energy to make it through the (mostly) winter energy expenditures).

I’ll touch on the energy budget first. It’s been often said that a deer or elk carries half of its winter range on its back. The fat on their backs in December depends on how low the body reserves were drained the prior winter, how much forage grows during summer/fall (fall green-up can be especially important), and the quality of the forage. For example, brush in old brush fields have much poorer digestibility than young brush fields, and invasive weeds such as Russian Knapweed may have fewer available nutrients and are less palatable to elk than many native forage species.

Elk can have energetic difficulties during winters that are especially long, especially cold or especially snowy, or have a snowpack with a crust that keeps elk from feeding or hinders movement. These factors all affect predation rates as well, but more on that later. What we typically see is some winter mortality by the time we do our flights in February, but most winter mortality occurs later, often during late March and early April.

In addition to direct impacts on elk calves during the year of the harsh winter, there are also serious impacts the following year as well. In fact, we find our lowest calf ratios the year after a harsh winter. Indications are that this is not so much a result of poor cow elk body condition leading to fetal death and absorption as it is low birth and growth rates of calves leading to poor calf survival (both malnutrition and predation). It’s often a two year impact, but if nothing further unusual happens, calf survival and calf ratios usually return to normal the third year. We had a severe winter 1996-1997, for example. Calf ratios hadn’t tanked by the time we flew our surveys in February (although they had dipped by then), but as shown in the harvest data the next fall, a lot of calves died later that winter. Calf ratios the following year were some of the lowest we’ve recorded.

Predation has always been a major player in determining calf survival, particularly in remote areas. Hunters and the Department had concerns about declining elk herds in the Lochsa in the early 1970s. Research then showed that of those calves captured in early June, 58% died by October 1st. Predation was almost entirely by bears and lions, with black bears accounting for about 74% of the predation, and lions about 22%. Between 1997 and 2003, elk calf survival was studied in the Lochsa again. By August 1st, 51% of calves had died, with cougars now accounting for about the same as bears. (During this period, wolf predation on elk calves was only about 1% during these first two months of a calf’s life.)

Habitat is also a key part of the predation picture. What researchers found in Idaho, is that the calf’s body weight at birth is very important. Data collected during the Lochsa study showed that a 2 pound gain in body weight was associated with a 9% increase in survival. A 2006 study in Wyoming found a gain of 14% for a 2 pound gain in body weight. The structure of the habitat may also play a role. In old, dense brush fields elk calves appear to have a harder time escaping predators (and our capture attempts) than younger, less dense brush fields.

Calf survival can be affected by a lot of factors, but the drivers are the annual energy budget (elk trying to make a living based on habitat and weather conditions), and predation (of course, this too is influenced by habitat and weather conditions).

Prior to 2009, we had 9 years of high calf ratios. Ratios changed abruptly starting 2009 (the year after the severe 2007-2008 winter). We saw reasonable recovery in calf ratios in 2010 (except Unit 7), and then no clear pattern beyond that. The 2013 data we have so far is slightly higher than those from last year, but not exceptionally so. Hopefully we can wrap this winter’s flights in the next week or two and finalize it all. Here’s where we are right now.

Our calf ratios are primarily a function of habitat, weather, and predator numbers. We’ve had 3 of our snowiest winters in history during the last 5 years, and last year even saw various records for a late spring, summer drought, and fall rains. It remains to be seen how much of an influence that was vs. predation an other factors.

OK, that’s it for now. We should have a better idea of season proposals in the next week or so, but I don’t really see any major changes in the wind for deer or elk seasons at this point.

Jim Hayden

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Rich Landers writes and photographs stories and columns for a wide range of outdoors coverage, including Outdoors feature sections on Sunday and Thursday.