Peak rut. The phrase quickens the pace of every serious deer hunter. When word goes out that “it’s on,” it’s time to drop everything and be in the woods. If we only knew what triggers it, we might be able to plan a little ahead.

The old timers used to say it takes a good cold snap. More recent prognosticators have resorted to various omens and triggers, some quite scientific — like moon phase, moon position, solunar tables and barometric pressure — some not — like rings around the moon, owl hoots at dusk or a good cold snap.

Fortunately there is a reliable source we can consult to find out when peak breeding occurs. For decades, deer biologists from every state and province where whitetails occur have kept tabs on the breeding chronology of their deer herds. These data paint a very clear and consistent picture.

According to research from the Department of Inland Fisheries and Wildlife, peak Maine breeding dates are Nov. 17-23 for mature does, followed a week later by yearling does.

Former Vermont deer project leader John Buck noted the peak of conception in his state occurred during the third week of November, while Massachusetts Division of Fisheries and Wildlife biologist Sonja Christensen cited the latter half of the second week of November, around Veteran’s Day as peak breeding.

Some of the more astute skeptics are probably wondering how these biologists know when peak breeding occurs.

After all, according to the more curmudgeonly, “them biologists never get out from behind their desks.”

One way to calculate peak breeding is to observe when fawns are born, then back-date the average 200-day gestation period to determine conception date.

Another is through fetal measurements. Biologists collect a sample of pregnant does from late winter through spring. Using a specially designed ruler they can measure the development of the fetus, and determine, within a day or two, the conception date.

Several points need to be considered. First, these dates represent a statistical high point, when the majority of does are breeding.

If you could picture it on a graph, this would be the peak, with declining numbers as you move in either direction – earlier or later. Though most does are being bred during this five-day peak, some are bred outside of it, a few well outside of it.

Second, and more importantly to the hunter, peak breeding and peak rut aren’t necessarily one and the same.

Most hunters consider peak rut as that magical time when mature bucks drop their guard and come out in broad daylight – a dynamic time of grunting and chasing. Biologically, peak rut is peak breeding. During this time hunters sometimes refer to as the lockdown, bucks and does have paired up and are sequestered off in some secluded area.

Though peak conceptions dates tend to be very consistent from one year to the next, there are exceptions. One occurred just to our northeast, where New Brunswick biologist Rod Cumberland observed what he termed an exceptional phenomenon.

“When our deer densities were high, peak rut here ran the last three weeks of November,” he said. “When numbers get below 100,000, we seem to drop later into a rut that runs the last two weeks of November and the first week of December.”

After several severe winters dramatically reduced their deer densities, the latter situation now seems to be the case, with the rut slipping back a week later.

With the recent dramatic decline in our statewide deer numbers, it’s entirely possible the same thing may be occurring here.

Bob Humphrey is a freelance writer and registered Maine guide who lives in Pownal. He can be contacted at: [email protected]

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