When we think of the first heralds of spring, we usually first think of spring blooms that
begin to emerge under the snow cover at this time of year, but this year one of the heralds
of spring appeared while the snow was still present. It is a brown bear (Ursus arctos L.) that
lives in the territory of the Republic of Croatia as part of the population of the Dinaric Massif
and which was caught by photo traps during a winter walk.
The brown bear in Croatia
The population of the Dinaric Massif is the largest population of brown bears in Central and
Western Europe and in Croatia there are about 1000 individuals. Males weigh an average of
210 kg and females 120 kg. They mate from April to early July and hibernate between
October and December. They spend the winter in specially selected and prepared dens,
which are most often found in cavities in the rocks. In rare cases, burrows are dug between
the roots of large trees and outdoors. In their dens they prepare a bed of dry grass, leaves
and twigs. During hibernation, they do not eat or drink and their body temperature
decreases by several degrees. Bear cubs are born during January or February, weigh about
350 g and are blind and hairless. For this reason, they are completely dependent on the care
of their mother from whom they are separated at the age of 1.5 years old.
Hibernation in the southern areas differs from hibernation in the northern areas. It doesn’t
last as long (or doesn’t happen at all) and depends mostly on food availability. Thus, it has
been proven that additional feeding affects the winter activities of bears. In Croatia,
hibernation lasts an average of 86 days, but recent research shows that hibernation is
getting shorter. Thus, for example, in neighbouring Slovenia, telemetry necklaces were used
to determine that males are hibernating on average for 57 days and females for 82 days.
Females with cubs stay longer in the den until the cubs are mature enough to follow the
mother. In the fall, bears, if they have sufficient food sources, create a subcutaneous layer of
fat that provides them with energy and water (metabolic water) for hibernation. Young
bears, which overwinter alone for the first time, often enter the winter unprepared and
therefore die. Pregnant females must create additional reserves for fetal development and
lactation, which is the most energy consuming process that occurs in mammalian bodies. In
addition, bear’s milk is among the most concentrated and contains about 22% fat and 12% protein.
Be careful in nature, no one likes to wake up too early!
Disturbing a bear during hibernation can result in the bear leaving its den, which means
inevitable death for the cubs if they are present since they are completely dependent on
their mother’s care. Leaving the den too early poses a great danger to the adult bears
themselves. Activation from sleep requires a lot of energy and is dangerous for adult bears if
there is still no food available outside. Therefore, all people who live in nature should be
careful not to disturb the bears during their hibernation.