‘Tis the season, and a few days ago I was able to observe part of the complex mating ritual that bears engage in during the months of May and June.
Estrus females eagerly laying down a scent trail traverse their territory at 3 times their normal rate.
The mating pair spends several days ‘getting to know’ each other. Females continue to forage during this time and generally can maintain their weight. Males, however, forage very little during mating season and lose approximately 20% of their fall weight over a period of 7-8 weeks.
[This loss is on top of the 20% of fall weight lost over the winter. This means a mature male weighing 500 lbs in the fall would leave the den in early spring weighing 400 lbs and would weigh 300 lbs at the end of mating season – and thus needs to regain those 200 lbs in 3 months to weigh 500 lbs again by fall.]
Couples often play and rest together during courtship. Males may follow individual females and guard them against rivals for up to 9 days before the cautious female becomes receptive and mating occurs.
Males have even been observed “herding” females into smaller and smaller areas in order to limit their scent-marking!
With the ‘wine & dine’ phase out of the way, mating begins, usually lasting only a few minutes at first. The pair mate repeatedly over several days, and some of the later copulations may last as long as an hour. (The event I observed lasted circa 45 minutes, thus probably was not their first encounter.) Sows may mate with one or several boars over the course of about a week.
After mating, the female may be pregnant, but that does not mean she will give birth to cubs. There is an old joke that you can’t be half pregnant, but bears have proven this statement to be false. Bears, weasels and some seals have developed a process called ‘delayed implantation’.
The fertilized egg develops into a small embryo called a blastocyst. After this brief period of development, the fertilized egg suddenly stops growing and simply floats freely in the uterus for several months.
If a sow is in peak condition when she heads into her winter den, the embryo implants in the uterus and begins to develop. She’ll wake up during January or February to give birth.
If the sow is not in peak condition at the onset of hibernation, her body will reabsorb the embryo and not give birth that year. This gives bears more control over their reproductive rate than just about any other animal.
Once an elk or deer is pregnant, for example, they are pregnant, and winter pregnancy can be fatal. Animals diverting energy to reproduction during the difficult winter months run the risk of falling victim to predation.
I would love to know how their teacher was handling this “teaching moment.”
🙂 🙂 🙂