Ask The Biologist

Split Personalities

Split Personalities

By Bob Humphrey

Hunter wants to know why deer in his area exhibit a sudden mood swing.

QUESTION: I deer hunt in northern Minnesota in the Grand Rapids area. There are a few hay fields in the area, but other than that it’s brush country. During the spring and summer, deer like to feed on new growth in the wide ditches and to escape the constant mosquitoes and deer flies. They are in their red summer coats and seem oblivious to the sightseers. But once they grow their winter coats in September, they become ever more spooky and less tolerable to humans. This behavior occurs even before small game and archery season starts. Is this a learned behavior from the does to the fawns for generations of the upcoming hunting seasons? –Steve B.

ANSWER: While we can never be certain of such things, it is likely the shift you observe is, at least to some extent, a learned behavior taught by a doe to her fawns. As for the reasons, that behavior is less likely related to the upcoming hunting seasons. That would suggest reasoning, an ability deer do not have, despite how they often outwit us.

It’s possible it could be indirectly related if human activity were to suddenly increase in the area – hunters hanging stands, setting trail cameras and clearing shooting lanes. But if, as you suggest, this is an annual occurrence, I suspect there may be other factors involved.

One of the most likely possibilities is diet shift. You mentioned deer were feeding on new growth in the ditches. Indeed, deer seek high protein foods throughout the summer, which is most often found in herbaceous vegetation like fields.

As the days grow shorter, things change. Herbaceous plants mature and die, suddenly becoming less nutritious and palatable. Meanwhile, deer begin gradually shifting their diet to foods higher in the cabohydrates they need to get in shape for the breeding season and lay on fat for winter. Outside of agricultural areas, most of those foods are in the woods in the form of hard and soft mast. The deer you’ve been watching might have simply left the salad bar and headed to the dessert table.

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