Female elk in Canada have become so good at avoiding hunters they are 'nearly invulnerable' once they reach the age of ten, researchers have found.

Researchers studied animals in Alberta and British Columbia, Canada and found they learnt a series of measure to keep themselves safe.

The older female elk reduced their movement and used safer grounds, and were even clever enough to differentiate between bow and rifle hunting seasons and alter their behaviour accordingly.

The older female elk reduced their movement and used safer grounds, and were even clever enough to differentiate between bow and rifle hunting seasons and alter their behaviour accordingly, the researchers discovered

'Elk learn to become shy as they get older,' University of Alberta biologist Mark Boyce told the Edmonton Journal.

'The magic number is 10,' said Boyce.

'After this age threshold, female elk become almost bulletproof, virtually invulnerable to hunting.'

'They hunker down in the deep forest and stay in rugged terrain. Those types of behaviours were very effective (for survival) in heavily hunted areas.'

Researchers fitted 49 female elk with ages ranging from 1-18 years old at the time of capture, in Alberta and British Columbia, Canada with GPS radiocollars, and tracked them for 2-4 years.

The data included distance traveled with time, terrain ruggedness (slope), and forest cover.

They found female elk learned behaviours that helped them better avoid hunters with each hunting season.

Male elk tend to live for only four or five years in Alberta because of their bold behaviour and hunters' preference for bull elk, Boyce said.

Their short lifespans meant they were not part of the study.

The researchers found that the older elk adjusted their behavior, suggesting that learning plays a role in shaping their avoidance of hunters.

Specifically, older female elk reduced their movement rates, thereby reducing their detectability and so the likelihood of encountering human hunters.

Researchers fitted 49 female elk with ages ranging from 1-18 years old at the time of capture, in Alberta and British Columbia, Canada with GPS radiocollars, and tracked them for 2-4 years.

In addition, older female elk increased their use of safer grounds -- rugged terrain and forest -- when they were near roads, where the likelihood of being spotted by hunters is highest.

The researchers also found that elk could differentiate between bow and rifle hunters.

Older females used rugged terrain more during the season for bow hunting than during that for rifle hunting, presumably reflecting the fact that bow hunters need to stalk their prey closely and this is more difficult on slopes.

Rifle hunters, in contrast, can shoot over distances of up to 300 meters.

This work may have implications for managers trying to impose behaviors on animals through learning; even a low risk, suggest the researchers, could induce avoidance behavior in more experienced individuals.