Mule Deer Better Mothers Than Whitetail Cousins (5/31/2007)

Mule deer are giving a whole new dimension to the term 'maternal instinct.'

An intriguing study of mule deer and white-tailed deer conducted by the University of Alberta and the University of Lethbridge shows that both species of deer respond to the recorded distress calls of fawns - cries similar to those elicited when coyotes attack fawns.

But mule deer mothers respond to the calls of any young deer, even when standing next to their own fawns. The white-tailed mothers respond only to their own species' call, and only when they cannot see their own offspring.

Researchers conducted the study by playing recorded cries of different types of fawns from a speaker.

"The fact that mule deer ran to the speaker when their own fawn was standing next to them - safe and sound - revealed they do not help other fawns because they mistake them for their own," said lead researcher Susan Lingle, who conducted the investigation as a postdoctoral fellow in biological sciences at the U of A and in psychology at the U of L.

"It was surprising just how indiscriminate mule deer females were. For example, the females that weren't even mothers also ran to the speakers to help fawns. That would not be expected if females were simply trying to protect their own fawns."

The results appear in this month's issue of Animal Behaviour.

In field trials using speakers that broadcast the calls of fawns under threat, the mule deer came to the speaker and stayed there as long as the calls played, twisting and turning as they confronted the perceived attackers. Whitetail mothers that came close to the speaker tended to withdraw right away and then stayed safely outside that distance.

The behaviour of mule deer defies traditional explanations that parental care, kin selection or reciprocity play a part in the protection of fawns other than their own. But while the study's findings seem to point to mule deer as superior mothers, the motivation for looking out for other fawns is likely based not on altruism but on simple survival, said Lingle.

"Having a rigid and aggressive response to the simple sound of a fawn distress call may ensure effective defence of a female's own offspring, even though this means the female invests time and energy and puts herself at risk by helping many other animals. In contrast, a white-tail mother waits to assess whether a fawn is her own before she steps in to defend it. As a result, white-tail fawns suffer considerably more predation during the first months of life than do mule deer fawns."

Mule deer may have developed a more aggressive defence because they rely on fighting to protect themselves against predators year-round, while white tails and many other species restrict aggressive defence to the youngest fawns. White tails rely on flight rather than fight most of their lives, so this may affect their ability to mount an aggressive defence," Lingle said.

This project was funded in part by the Alberta Ingenuity Fund and the Natural Science Engineering and Research Council of Canada.

Note: This story has been adapted from a news release issued by the University of Alberta

Post Comments: