A Whitetail’s Depressed Winter Metabolism – Fact or Fiction?

Posted on February 12, 2013

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 (Part II of a 2 part series)

 

(The last post we looked at the hypothesis regarding a whitetail’s ability to reduce its metabolism and concluded with how researchers tested deer to either support or debunk this theory. We will now look at the results along with additional information regarding wintering whitetails and their incredible adaptations.)

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Throughout the northern portion of the whitetails range, from December till April, deer are significantly tested by what old-man winter throws at them. According to nature photographer and writer, Charlie Alsheimer,

“While it’s happening you swear that there is no way any whitetails can survive nature’s dose of cold and snow. But somehow most deer figure out a way to make it through to springs green-up. Every time I think about what a whitetail must go through I’m in awe of their resilience and will to live another day.”

The Results

For the five does tested, body mass (BM) did not differ monthly, although the mean loss in BM was 14% by March. Peak BM occurred during November with the highest percentage drop occurring between December and February. Body fat (BF) was at its lowest in both September and March, but significantly peaked in December. BM and body fat increased from September into December. Continuous increase in BM & BF can easily be attributed to and influenced by reduction in activity and digestive efficiency resulting in extra energy for conversion to BM.

According to Pekins’ study, “Deer in the wild presumably undergo more distinct cyclical changes in body mass as the result of a lower quality diet and the energetic expenditures associated with travel, which our research animals did not experience.”

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Interestingly, after a 1969 study of fasting deer by H. Silver, he then hypothesized that, “reduced feed intake, body mass, and activity could be attributed to a depression in winter FMR”, but Pekins’ research did not find any significant relationship between FMR and fat loss as suggested by this hypothesis. Additionally, subsequent measurements have not revealed such depressions. According to Pekins, “We found no significant correlation between the fat cycle in the experimental animals and changes in FMR.”

Despite the recent research results, the following information certainly gives one pause to at least consider the viability of whether or not depressed metabolic rate in wintering whitetails is just a myth. “Metabolic rate is influenced by the nutrition of the animal prior to the metabolic trial, and it has been shown that under nourished animals have a depressed metabolic rate (Kleiber 1975; Hudson and Christopherson 1985). The lower quality diet of wild deer during this time of year suggests that their FMR could be lower than that of our research animals.”

Fat

If only we humans could convert our accumulated body fat into an energy source the diet industry would go broke, and guess what, we’d probably be a lot healthier in the process. The white-tailed deer’s reliance on accumulated fat is indeed one of the key innate attributes that sustain them. As a former UNH student of Pekins, QDMA’s, Kip Adams weighs in with the following, “Since deer don’t dramatically decrease their metabolic rate during winter, how do they survive harsh winters? Body fat is the key physiological component of winter survival. Whitetails gain weight during fall to use as an energy source during winter. Winter nutrition comes from stored fat supplemented with browse such as buds, twigs and dead leaves. Adult does can get more than 50 percent of their daily nutrition from their fat reserves. The key to winter survival is depositing as much fat as possible during fall and then reducing activity, and thus fat usage, during winter. A deer population’s ability to do this is directly related to habitat quality.”

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To help them accomplish this one of the best available foods for most free-ranging deer is acorns. When abundant, whitetails will gorge themselves on this fruit exclusive to all other natural browse in the fall, and routinely dig through several inches of snow to get at any residue nuts during winter.

The Debate

Man living in snow country physically prepares himself for winter by hauling in a wood supply, insulating drafty windows, storing up goods grown throughout the summer etc…A whitetail has no such game plan, they are not capable of planning for future events. Whitetails live exclusively in the present with two primary goals, eat and keep from being eaten. With that being stated, each winter when snow depths reach 18” or greater and the temperatures rescind below 19 degrees Fahrenheit, whitetails begin to migrate to their traditional winter yards. In less harsh environments, such as farm country, whitetails may only move to south facing locations. But in both cases a whitetail’s response to winter is identical.

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Behaviorist, Charlie Alsheimer, who has observed whitetails for over 30 years, both in the wild and within his research facility located in western New York, makes this assertion about whitetails during winter months:

“A biological shift within all whitetails occurs as they adjust to winter. During the early part of winter they have reduced thyroid function and decreased metabolic activity. This results in less food being needed for survival. Then by mid-winter their system slows down even further and they enter a time when they are almost hibernating on the hoof. Scientists refer to this as a semi-hibernating state. It allows deer to become quite resistant to nutritional deprivation and the stresses of winter’s harsh climate. This phenomenon reduces a deer’s food intake by approximately 30%, regardless of the food available, and their activity by up to 50%.

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The downside of their movement reduction is that they become very reluctant to move from a given location to another to find food when they go into semi-hibernation. I’ve seen this behavior exhibited often when I’ve gone into a particular wintering area to cut browse. During tough winters I’ve had to cut trees within three hundred yards of where the deer were bedding just to get them interested in the new cache of food. Other times I’ve seen them half a mile from very good browse and not desirous enough to look for it. It’s almost like the food had to be right under their nose. This complicates matters because during winter months they need at least six pounds of browse a day to survive. And if they don’t move to look for food their condition deteriorates quickly.”

Conclusion

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Regardless of which side of the fence you may be on, or if it even matters to you, the very fact that whitetails have demonstrated a capacity to endure harsh northern winters attests to the deer’s remarkable behavioral and genetic plasticity, and reflects its ability to cope with sharply contrasting environmental conditions. As the slogan reads on the Fox News channel – We report – You decide.

All images and text on this site are copyright protected and the property of R.G.Bernier

© 2013 R.G. Bernier Nature Photography – All rights reserved.

 

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Posted in: Whitetail Deer