For elk, being bull-headed is a natural selection
USA TODAY's Dan Vergano
"Nature, red in tooth and claw," wrote the poet Alfred Lord Tennyson. Mourning the death of a friend, he also penned a catchphrase for ecologists, who see his poetry in action. One natural laboratory in which tooth and claw play out their drama is the American West, where studies of wolves and elk are a cottage industry.
How elk respond to wolves on the Gallatin range in southwestern Montana is one of the venues for these studies. Wolves only re-entered the range in 1996, after they were wiped out by trapping and hunting in the 1920s. One example of wolves' impact comes from observations of willow trees, which an Oregon State University study in 2004 suggested rebounded in numbers along Gallatin streams following the wolves' arrival. One implication was that elk felt less free to snack on willows once wolves started hunting them down, as woods and streams present obstacles to escape.
A new study by Montana State University's Scott Creel and John Winnie, Jr., in the current Animal Behavior journal, suggests elk may not be all that clever about trees though. Or wolves. Particularly male elk, aka bulls.
Elk life is a fairly steady cycle of sleeping, walking, watching for threats and eating, with emphasis on the last item, with grazing taking almost two-thirds of their time. Throwing wolves into their lives was expected to change their patterns, the researchers said, noting that "prey often alter their behavior in response to changes in predation risk" in everything from tiger sharks to barn owl prey species.
The study looked at elk herds over three winters from 2001 to 2003. Elk of both sexes on the Gallatin range moved closer to timber when wolves were around, likely using the woods for cover, despite the willows study. And herd sizes, whether of bulls alone or mixed sexes, shrank as well, typically to a size of six to nine elk. Small herds are harder for wolves to spot.
But the researchers report that throwing wolves into the mix didn't change too much overall; the elk still spent much of their time eating, sleeping and moving in roughly the same proportions. And the amount of time that the elk spent being vigilant didn't change much, whether they were close to timber or out in the open.
But a closer look at the data showed that female elk, or cows, spent more time being vigilant and less time grazing when wolves were around. Bulls, not so much.
That was surprising, because the researchers have shown in past work that wolves in the Gallatin range are roughly six times more likely to kill bulls than cows, particularly in winter. An answer to this riddle may come from looking at the bulls killed, they suggest. They tend to have been old or sick, with lower bone marrow fat than cows killed by wolves, according to a study of their wolf-gnawed remains. "Wolf-killed bulls were in worse physical condition than wolf-killed cows throughout the winter," they write.
Why? Basically, it's hard to be a bull out there. In order to compete in the annual rut, in which bulls square off for breeding rights to cows, you need to be a big, strong bull. And if you want to reproduce, evolution's dividing line between success or failure, that means eating a lot. And then burning up that fat by repeatedly beating your antlers against the head of another similarly-stuffed, and well-motivated, bull elk.
As a result, "bulls are less able to pay the foraging costs of responding to wolf presence by increasing vigilance," they conclude. So the bulls, forced to eat rather than watch their backs, end up as wolf chow. (None of this, of course, even remotely suggests anything about the corn-chip-eating, chest-thumping and generally inattentive behavior of human males, whose lifespan the biological anthropologist Richard Bribiescas has Dylan-esquely described as "stud, dud, thud.")
Bulls may suffer a bit from overconfidence, too. "Bulls, which are about 30% larger than cows and carry antlers, may represent a more dangerous adversary than cows, so that wolves do not risk attacking bulls until the bulls are in poor condition," the researchers suggest. That's natural selection for you, as Charles Darwin might have put it, when he wrote On the Origin of Species in 1859, less than a decade after Tennyson's poem.
USA TODAY's Dan Vergano
"Nature, red in tooth and claw," wrote the poet Alfred Lord Tennyson. Mourning the death of a friend, he also penned a catchphrase for ecologists, who see his poetry in action. One natural laboratory in which tooth and claw play out their drama is the American West, where studies of wolves and elk are a cottage industry.
How elk respond to wolves on the Gallatin range in southwestern Montana is one of the venues for these studies. Wolves only re-entered the range in 1996, after they were wiped out by trapping and hunting in the 1920s. One example of wolves' impact comes from observations of willow trees, which an Oregon State University study in 2004 suggested rebounded in numbers along Gallatin streams following the wolves' arrival. One implication was that elk felt less free to snack on willows once wolves started hunting them down, as woods and streams present obstacles to escape.
A new study by Montana State University's Scott Creel and John Winnie, Jr., in the current Animal Behavior journal, suggests elk may not be all that clever about trees though. Or wolves. Particularly male elk, aka bulls.
Elk life is a fairly steady cycle of sleeping, walking, watching for threats and eating, with emphasis on the last item, with grazing taking almost two-thirds of their time. Throwing wolves into their lives was expected to change their patterns, the researchers said, noting that "prey often alter their behavior in response to changes in predation risk" in everything from tiger sharks to barn owl prey species.
The study looked at elk herds over three winters from 2001 to 2003. Elk of both sexes on the Gallatin range moved closer to timber when wolves were around, likely using the woods for cover, despite the willows study. And herd sizes, whether of bulls alone or mixed sexes, shrank as well, typically to a size of six to nine elk. Small herds are harder for wolves to spot.
But the researchers report that throwing wolves into the mix didn't change too much overall; the elk still spent much of their time eating, sleeping and moving in roughly the same proportions. And the amount of time that the elk spent being vigilant didn't change much, whether they were close to timber or out in the open.
But a closer look at the data showed that female elk, or cows, spent more time being vigilant and less time grazing when wolves were around. Bulls, not so much.
That was surprising, because the researchers have shown in past work that wolves in the Gallatin range are roughly six times more likely to kill bulls than cows, particularly in winter. An answer to this riddle may come from looking at the bulls killed, they suggest. They tend to have been old or sick, with lower bone marrow fat than cows killed by wolves, according to a study of their wolf-gnawed remains. "Wolf-killed bulls were in worse physical condition than wolf-killed cows throughout the winter," they write.
Why? Basically, it's hard to be a bull out there. In order to compete in the annual rut, in which bulls square off for breeding rights to cows, you need to be a big, strong bull. And if you want to reproduce, evolution's dividing line between success or failure, that means eating a lot. And then burning up that fat by repeatedly beating your antlers against the head of another similarly-stuffed, and well-motivated, bull elk.
As a result, "bulls are less able to pay the foraging costs of responding to wolf presence by increasing vigilance," they conclude. So the bulls, forced to eat rather than watch their backs, end up as wolf chow. (None of this, of course, even remotely suggests anything about the corn-chip-eating, chest-thumping and generally inattentive behavior of human males, whose lifespan the biological anthropologist Richard Bribiescas has Dylan-esquely described as "stud, dud, thud.")
Bulls may suffer a bit from overconfidence, too. "Bulls, which are about 30% larger than cows and carry antlers, may represent a more dangerous adversary than cows, so that wolves do not risk attacking bulls until the bulls are in poor condition," the researchers suggest. That's natural selection for you, as Charles Darwin might have put it, when he wrote On the Origin of Species in 1859, less than a decade after Tennyson's poem.
