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American Association for the Advancement of Science

Elk change physiology when hunted by wolves

The wolves of the Greater Yellowstone Ecosystem affect elk in important ways besides making meals of them, researchers have found.

The wolves do hunt the elk for food, but scientists at Montana State University found that the elk respond to being hunted using something called inducible defenses that plants, invertebrates and vertebrates rely on. These living beings may change their bodies or behavior when they are vulnerable and hunted.

Wolves were reintroduced to the Greater Yellowstone Ecosystem in 1995 and 1996. The number of wolves grew rapidly; the number of elk declined. Researchers studied the elk between 2002 and 2006 and found that in addition to changing their habitat, grouping patterns, vigilance and foraging, the female elks' progesterone -- a hormone involving the females' readiness for pregnancy -- decreased in populations that were hunted relatively heavily by wolves.

The female elk, called cows, also bore fewer calves than cows in groups that were not hunted as aggressively. Researchers also found that females show stronger responses to being hunted by the wolves than the males and fewer females are killed by wolves than male elk.

Researchers determined that the pressures of being a predator can be more than losing one's life.