In this article we are going to discuss about polar bear giving birth to its cubs as well as the bear’s birth interval.
How often Do Polar Bears have Cubs?
Studies indicate that most females wean their cubs after two and a half years, which suggests that they can afford to mate once every three years. According to scientists, the female bears inhabiting Beaufort Sea are thought to mature earlier than those living in other areas. The weaning time and the birth interval of Beaufort Sea population is the same.
In 1990s
In rare instances, scientists have also observed female polar bears keeping their babies for as long as three and a half years. In the 1990s, a few individuals reported to wean after three and a half years in the Viscount Melville Sound. Even so, another female reported to have her cubs around her for up to four and a half years. According to Ian Stirling the likely reason could be that bears were probably living in less productive habitats where multiyear sea ice didn’t occur as much. Plus, the ringed seals weren’t abundant in the Viscount Melville Sound. As it turns out, a less accessible food might have probably slowed the growth rate of polar bear cubs, resulting in a delay in the age at weaning.
Another explanation for the delay in weaning (in 1990s) could be due to overharvesting in adult males. The adult males could have been less frequent which would drive away the cubs from their mother. However, Viscount Melville Sound isn’t protected by multiyear sea ice anymore perhaps due to climate change therefore; polar bears can afford to hunt ringed seals.
In 1980s
If we go back to the 1980s we observe 40% of all polar bear females could successfully wean their cubs at only one and a half years of age in the western coast of Hudson Bay. As it turned out, nearly all females would breed every two years which may have allowed them to produce 30% more litters in their entire lives.
Nonetheless, when scientists compared the mortality rate in yearlings that were weaned right on time against those which took additional time, they found interestingly no major difference. Both had lived more than their average lifespans. They also observed that the survival rate of one-year-old cubs in the Hudson Bay was probably the same as that of two-year-old cubs inhabiting rest of the Arctic.
Why the Hudson Bay Females are more Productive than others
- Studies indicate that some of the females in the western coast of Hudson Bay have successfully raised their cubs so that the yearlings hunt on their own. The reason behind is that the snowdrifts in the Hudson Bay melts relatively earlier, and as it softens, the yearlings which are probably not too heavy to break the ice, can hunt ringed seals at their breathing holes.
- Another reason as to why Hudson Bay females produce more frequently than others is that the Hudson Bay itself is biologically productive. The rivers that end up with the Hudson are thought to bring many nutrients which indeed attracts large seal population. Since they are the primary food of arctic bears, the bears of all ages might have less difficulty catching food.
- Studies have also shown that the Hudson Bay is home to a large number of bearded seals. The bearded seal is nearly five times the size of a ringed seal. The larger food source means larger carrion remaining on the sea ice. Yearlings often find it hard to hunt and so they mostly rely on left-over carrion. They are going to eat seals by scavenging the kills until they are big enough to hunt on their own
