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There are about 700 brown bears in the Estonian forests, and about 140 of them are mature females. In nature bears may reach an age of 30 – 40.

 

A female bear doesn’t become sexually mature until at 4-5 years, and after that has cubs at intervals of 2-4 years. The female bear has a so called delayed implantation development process, that is, after the mating which may take place between the end of April and June the fertilized egg cell will attach to the uterus wall only after the bear has gone into its winter sleep. Foetuses then become fully developed within a couple of months.

 

Brown bears fatten up thoroughly for the winter sleep. Their winter sleep is comparable to a vigilant ordinary sleep: the body temperature drops to 32 C, the heart beats about 10 times a minute whereas normally their pulse is at 40 beats per minute. During this period the digestive tract of the bear doesn’t work, no excrements or urine are produced, and they don’t eat but use up the stored fat reserves during the sleep – about 300 grams of fat per day. In this way an individual weighing a couple of hundred kilos may become slimmer by up to 40 % of its body weight. The numbers are theoretical; in reality they would depend on the specific individual, but provide an idea of the magnitude.

 

As the foetus develops and the time to give birth approaches the temperature of the pregnant female bear rises up to the summer level, about 37 C. Giving birth is an energy-consuming process; the newly born cubs need warmth as do the milk glands in order to work.