Older and wiser: Female elk can learn to avoid hunters with age

Once female elk reach the age of about 10 years, they are nearly invulnerable to human hunters. This age-related difference could be driven only by selection by hunters -- or it could also be driven by learning. If learning is not involved, then individuals should not adjust their behavior as they age; for example, elk that survive could simply have been more cautious all along. If learning is involved, however, then individuals should adjust their behavior as they age. Female elk are ideal for differentiating between these two hypotheses, in part because they are highly gregarious and can live upwards of 20 years, increasing the opportunities for learning.

Thurfjell and colleagues 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. The researchers then modeled elk with behaviors that differed amongst individuals but were constant over time in a given individual, as well as elk that could learn to adjust their behavior with age.

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. 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. Interestingly, 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.