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The Ungulate Mating Calendar Demands Tight Timing

Skeeze - Pixabay

I've seen white-tailed does and fawns in my yard all spring and summer. But just last week I saw two bucks. Why would bucks show up now, when it seemed that only does and fawns lived in the area? Well, if spring is for the birds, then fall would have to be the season for ungulates.

Fall is the time of year when Montana's large grazing animals - bison, elk, antelope, moose, deer, bighorn sheep and mountain goats - engage in their various mating rituals.

From August through November, the different species go on a hunt of their own to reproduce. Males leave their summer haunts and join females, becoming defensive of territories and breeding when the time is right. This is the time of year when elk are bugling, bighorn rams are clashing horns and white-tailed bucks with swollen necks roam the countryside looking for females.

The timing of these mating seasons, or the rut, is not quite as backwards as it may seem. Basically, these young need to be born in the spring. So to accommodate the long gestation period of large mammals, they must be conceived in the fall. Being born at just the right time is crucial for the young’s survival. Too early means increased danger of exposure to late snows and lack of succulent green forage needed by mothers to produce milk. Too late does not allow the young time to grow enough to survive the following winter.
The rut is triggered by photoperiod, or day length, and is not subject to delays due to weather, as is commonly believed. Basically, the young have to be born at the same time every year, which is around mid-May to mid-June for most species in Montana.

So Montana’s ungulate breeding calendar is a full one, beginning of course, with the largest mammal in the state, which requires the longest time for young to develop: the bison.

The bison rut takes place in August, before we're even thinking of fall. Dominant bulls defend groups of females from other males to maintain breeding rights. Loud roars reminiscent of African lions echo from bison herds as males assert their dominance and occasionally engage in spectacular pushing matches with their massive heads.

The next ruts to take place, as we might expect, are those of elk and moose. These species breed in September and early October, with the elk rut preceding the moose rut by a week or two. The familiar bugles of bull elk resound from the mountains at this time as they defend female groups from other males.

Moose, although far less showy, do vocalize and have a mating ritual of their own. Bulls emit soft grunts while females have long whining calls. Moose are more solitary than elk, though, and generally do not defend harems.

Mule deer, white-tailed deer, bighorn sheep and mountain goats all go through their rutting periods in mid-November. They're smaller and have shorter gestation periods than their larger relatives. Although not thought of as vocal, they all make sounds, generally in the form of grunts.  Mule deer bucks emit a loud wheeze when confronting a rival. The first time I heard this, I wasn't sure which end of the animal it was coming from.

Bighorn sheep are well-known for their head-clashing battles, making a resounding crack which can be heard from a distance. And the exception to the rut timing schedule are the pronghorn antelope, the smallest of Montana's ungulates. They mate about the same time elk and moose do.

So as you go afield this fall, take notice of the mating behavior around you. The does you've seen all year will soon have bucks among them. Our national parks, the National Bison Range and the national forest land all around us are great places to watch the show. Next spring's fawns, calves, kids and lambs are all depending on it.

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Fieldnotes," 11/17/13, 09/20/16, 09/22/20 and 09/25/20. Listen weekly on the radio Tuesdays and Fridays at 4:54 p.m., or via podcast.)

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