While a few mule deer are known to basically stay put in specific areas year-round, most migrate between summer and winter ranges, Wilde said. Distances can be only a few miles, and most deer aren’t known to travel more than about 100 miles each way.
However, extended migrations like the ones 255 take might make for larger, better and longer-lived deer, he said.
In addition to her unusual longevity, Deer 255 also is huskier than most mule deer does, he said. Most does weigh about 140 pounds. Deer 255 tips the scales to a robust 170.
It could be that traveling longer distances as the seasons change has allowed her to “ride the green wave,” he said.
Meaning that, during the spring, she follows the lushest food sources northward, moving onward before an area starts to dry out, Wilde said. Likewise, on her way back south and downward in elevation during the fall and early winter, she stays ahead of the snowfall, enjoying the best available food sources as winter closes in behind her.
Deer that don’t travel as far don’t have that advantage and are pretty much stuck with whatever they find within their limited ranges, Wilde said.
That could mean the urge to migrate long distances is genetically embedded in some mule deer, he said. Deer 255 could have come from a line of deer that migrated far. And her fawns might continue to trek vast distances across Wyoming after she’s gone.
It’s thought that a fair number of her fawns have survived, Wilde said, though there’s no way of knowing for certain.
She had a single fawn in 2016, and birthed twins each spring from 2018-2022.
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How Long Does The Journey Take?
The time Deer 255 puts into her treks varies. She has numerous “stopover” places along her preferred travel routes where she might linger for as long as 20 days, Wilde said. The rate of snowmelt and when and where her fawns are born each spring factor in.
Sometimes she takes months to amble down to the Red Desert and doesn’t arrive on her winter range until mid-January, he said.
“During some years, this same deer will zip all the way down in a week” if the snow comes early and hard enough, Wilde said, adding that mule deer can frequently travel 20-40 miles a day when migrating.
Deer 255 is loath to leave her summer stronghold in Jackson Hole because the living is good there, Nickerson said. She’s picked hangouts in high, steep country where to forage is good, but the roughness of the country discourages people from going in.
Only when the snow starts to fly thick will she leave, he said. But when it does, she has to hurry out because the area quickly accumulates several feet of snow.
There’s no telling when Deer 255 will take her last steps, but Nickerson said he hopes that’s not for a while yet.
“She catches our attention as humans and biologists,” he said. “She serves to teach the public about how the migration story is important to these animals.”
