The Annual Migration – Part I

Posted on February 7, 2012

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(Part I of a three part series)

 

“Doubtless the great depth of snow was the original cause of the fall migration of deer, and the habit had finally become so fixed by inheritance that long before there was any apparent necessity, the retirement took place.”

                                                                            – George Shiras III

Like a caravan of Gypsies moving to better digs, the white-tailed deer residing in the northern fringe of its habitat make their annual pilgrimage back to the winter yards. This rhythmic occurrence has for countless generations given whitetails living on the harsh northern range the ability to cope with the many stresses brought on by a severe winter, and facilitated survival despite what may appear as overwhelming odds.

How do the deer know when it’s time to make this pilgrimage? What triggers them to start? Without maps, compasses, or GPS how do they find their way back each year, especially when this journey could include upwards of twenty miles distance or more? Does every whitetail participate, and is the migration a simultaneous event involving an entire herd? And finally, what prompts these same animals to make the return trip back to their summer range in the spring?

 

The Exodus

Beginning as early as late October whitetails can and do start to march towards their wintering grounds. Usually this journey doesn’t start until late November, but there are exceptions. Biologist Michael Nelson has conducted research on migratory whitetails in Northeastern Minnesota since 1975. His studies include numerous radio-collared deer that he constantly monitors throughout the autumn, winter and spring seasons. Of the 149 females tracked during the fall, two migrated weeks (October) before other females followed suit. In both cases, these two particular females exhibited this behavior for three consecutive years. Although this behavior is considered somewhat abnormal, it certainly proves that some deer do indeed begin the trek well in advance of the rest of the herd.

For most northern whitetails there are a variety of factors that help trigger their migration from summer range to winter habitat. Although the onset of fall migration and permanent arrival of deer on winter ranges has received little study, there are several aspects that have been observed which coincide with the animal’s departure. According to Michigan biologist John Ozoga, “Most investigations of whitetails’ migratory behavior reveal that cold temperatures serve as the primary stimulus prompting deer to seek heavy cover that provides them maximum physical comfort. Mounting snow depths may later act to restrict deer movement to core areas of the best shelter, but, in itself, snowfall seldom seems to cause migration. In fact, most deer migrate to winter yards long before snow becomes deep enough to seriously obstruct their travel.”

 

Nelson’s ongoing study results reiterate this point. “Fall migration consistently started following the first temperatures below -7° C (19° F), which occurred during late October in 3 years and during November in 14 years. Measurable snowfall also accompanied or shortly preceded these decreasing temperatures and first migrations, except during 3 years when some deer migrated before it snowed.”

Despite this research, given the fact that whitetails are an unpredictable creature, the migratory response of deer tends to vary each year between areas and even within the same area. There are even neighboring family groups of deer that will demonstrate different migratory dates even though they are exposed to the same conditions. Nelson found that although a high percentage of deer migrated to winter ranges during a prolonged cold snap, even during November, others stalled until temperatures actually began to increase before making their move. Then there were those deer that remained staunchly on summer range until December and January when snow depths began to escalate.

 

Although temperature seems to be one of the key impetuses that triggers whitetails to begin moving towards winter grounds, I have personally witnessed deer heading for yards following both a late October snowfall (2000), and a mid-November drop (1985) where snow depths reached significant levels. In both of these situations, once temperatures increased and the snow receded to less than five inches the deer returned to their summer range. It would seem they intuitively realized that feed was still better and more abundant than what their wintering ground would offer. Obviously, this is conjecture on my part due to the fact that I’ve yet been unable to converse verbally with any hoofed animal.

 

The Nutritional Aspect

It appears that nutrition may also be an important variable influencing migration dates. According to Nelson, “Nutrition may also affect the physiological threshold to thermal changes that induce migration.” Much like bears, where a plentiful supply of mast delays hibernation, deer that are foraging on highly nutritious feed that is rich in energy may indeed prolong their stay on summer range.

 

It must be remembered that a whitetail survives the cold and stress of winter months through a delicate balancing act. The animal must be able to consume enough food to generate warmth as well as be afforded adequate protection from the bitter, heat robbing wind. If snow depths are not an issue and food is in abundance, despite low temperatures deer may not opt to migrate. Because deer inherently reduce their metabolism, a survival mode known as ‘walking hibernation’, the amount of food that is required to sufficiently maintain them is reduced considerably. In my nearly four decades of studying this animal I’ve seen several instances where deer have begun to move towards their wintering grounds only to abruptly stop where a logging operation was in full swing. The easy pickings provided by the logger’s chain saw, and given the fact that most north country cutting operates within stands of dense softwood, provides the whitetail all the ingredients necessary to survive the winter without going to the yard. The down side to this dangerous and often fatal gamble for these animals is a sudden increase in snow depths and diminishing food supply. Although feed within their traditional yard may not be as nutritious, the ability to form endless escape trails and retain warmth provides a much better advantage when it comes to survivability.

 

The Duration Of The Trip

Obviously a longer travel distance to the yard requires a greater amount of time needed to get there. I know of two deeryards in Maine where deer march in excess of twenty and thirty miles in order to arrive at these wintering grounds. One of these requires several family groups to come over a significant mountain range. It must also be understood, like the Serengeti migration of wildebeests and buffalo in Africa, and the caribou of the Canadian province of Quebec, whitetails are not in a constant uninterrupted march to get there. Minnesota biologists, Orrin Rongstad and Tim Lewis found when studying migrating whitetails that fall migration was not a direct movement from summer to winter range. Most deer took from 24 to 31 days to complete the trek.

 

Next week in Part II we will look at how many deer actually migrate, how they find their way, if bucks exhibit the same behavior, and if this ritual is ancestral.

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

    © 2012 R.G. Bernier Nature Photography – All rights reserved.

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Posted in: Whitetail Deer