( s likely based not on altruism but on s...)Mule deer moms rescue other fawns

"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 whitetail mother waits to assess whether a fawn is her own before she steps in to defend it. As a result, whitetail fawns suffer considerably more predation during the first months of life than do mule deer fawns."

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

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Source:University of Alberta