• Alex Taylor

Mummy's Cubs

The hunting of brown bears in Sweden is causing a change in the mother bears' behaviour. To avoid being shot and killed, they are keeping their cubs with them for a whole year longer than they were just a few decades ago, a change that may have serious repercussions for their survival.

Mother brown bears are using their cubs as protection

Like all bear cubs, brown bear cubs in Sweden’s forests stay with their mothers until they have learned how to survive in the big, bad world. In Sweden, it’s a dangerous world to be in because bears can be shot by anyone, no specific licence required. And sadly, they are heavily hunted.

The exception however, is mother bears with cubs – every other bear is fair game, but it is illegal to shoot a mother with cubs. It seems that this has changed the behaviour of the bears, and hunting is now acting as a selection pressure.

Mother bears have two choices. They can look after their cubs for a shorter period of time, which allows them to breed again the following year, or they can keep their cubs with them for longer, resulting in them having fewer litters. It turns out that Sweden’s mother bears are choosing the latter strategy, and are keeping their cubs with them for longer as a way of avoiding being shot by hunters.

Twenty two years’ worth of data was analysed on the way to making this discovery. Information on survival and reproduction in a heavily hunted, and well-studied, bear population that lives in the middle of the country was used. Thus, it is one of the longest-running research projects on bears.

Throughout the 1980s, Scandinavian bear cubs used to stay with their mothers for only a year and a half. Then mama bear had a new litter the next year. This continued up until 1995, but after this time there has been a shift towards staying by their mum’s side for longer. A whole year longer. Between 2005 and 2015, the number of females that kept their cubs with them for two and a half years rose from 7% to 36%.

Hunting regulations that don’t allow for the killing of mother bears with cubs seems to be favouring longer maternal care in this population. If this behaviour is genetically determined, ie if mothers who care for their cubs for longer pass on this trait and give birth to daughters who also care for their cubs for longer, then this could lead to evolution in the population. The trait will be passed from generation to generation and hunting by humans will filter out the females who keep their cubs with them for a shorter amount of time.

Even though it means that female bears end up having fewer breeding opportunities, and fewer cubs in their lifetime overall, this cost is outweighed by the higher chances of their own survival. It’s like they are using their cubs as a shield, to protect themselves from being shot. And I don’t blame them – a female on her own is four times more likely to be shot than a female with a cub.

Sweden’s bear hunting is apparently sustainable as the size of the population is stable, but this change in female bear reproduction could point to an increasing hunting pressure. And by changing their reproduction, long term adverse consequences could ensue. The bears’ population structure could change, and a larger proportion of reproductive females would clearly impact future survival.

This means that, simply because we want to kill bears, our actions could have serious consequences on this population. And this is just one bear species – how many others are affected in this way? Our behaviour can alter animal behaviour drastically and slow down their lifecycle. We are impacting their survival in so many ways.

#animalbehaviour #bears #hunting