Shrinking horns case raises fears for hunted species

A research team led by Dr. David Coltman of the University of Sheffield has discovered that hunting may permanently change the physical characteristics of the targeted species.

Dr. Coltman, of the University’s Department of Animal and Plant Sciences, is part of a team investigating effects of thirty years of trophy hunting bighorn rams at Ram Mountain in Alberta, Canada. Trophy rams are heavy, with rapidly growing horns, and are a valuable commodity.

Trophy hunting at Ram Mountain is unrestricted, being limited only by the size of the ram’s horns, and any ram reaching the minimum size can be legally shot. Eighty-five per cent of the rams shot since 1975 have been under the age of eight. This gives rams with rapidly growing horns little time to breed, as mating is generally more successful from the age of six, when rams can use their horns to fight for females.

By culling the trophy rams before they have a chance to pass on the gene that causes trophy characteristics, hunters are effectively wiping them from the population. As a result, trophy rams are becoming more rare and the general population of bighorn rams is lighter, with smaller horns.

Dr Coltman explains, “Our research shows that targeting a particular characteristic for hunting can seriously affect the appearance of future generations of a species. Basically, the sought after trait will become more rare as the genes for that characteristic becomes less frequent among the population. This can also be seen in Africa, where tuskless elephants have become more common in response to hunting for ivory.

“It is important to remember that this response in the bighorn ram population has occurred in only thirty years, a very short time in terms of evolutionary change. Our research has implications for the future of unrestricted hunting, and suggests that stricter guidelines are needed to ensure that hunters don’t further contribute to the decline of the very traits that determine trophy quality. These changes are extremely difficult to reverse and prevention is easier, and more effective, than cure.”