Edit ModuleShow Tags
Edit ModuleShow Tags

The Alaska porcupine¹s winter in slow-motion


While running through Bicentennial Park in Anchorage, biologist Jessy
Coltrane spotted a porcupine in a birch tree. On her runs on days following,
she saw it again and again, in good weather and bad. Over time, she knew
which Alaska creature she wanted to study.
"I thought, 'Oh my god, how does he do it? How does this animal make it
through winter?'" Coltrane said during the December defense of her doctoral
thesis in Fairbanks. "It would be 20 below out and he¹s there eating
Coltrane's study has cast some midwinter light on the Alaska porcupine,
perhaps the least-studied mammal in the state. She at first wanted to learn
about what porcupines did in winter, but switched to studying the physiology
of the quilled creature after the porcupines she watched hardly moved on
their tree-limb perches. Winter porcupine behavior "doesn¹t happen," she
joked at her defense.
But that lack of activity in a subarctic winter made porcupines more
intriguing to her. The porcupine doesn¹t avoid winter by hibernating like a
bear, nor does it curl up in an earthen womb like the beaver (the only
larger rodent in Alaska). She saw porcupines most often in trees, with no
protection from the elements.
 In designing her study, Coltrane mused about the challenges of an exposed
life during an Alaska winter. Bitter air temperatures would probably require
a porcupine to take in more calories, she thought. This seemed puzzling when
a porcupine¹s major food was to be the inner bark of white spruce trees and
the tree¹s bitter needles, rich with toxins that discourage most every other
animal from chewing them.
To begin her study, she searched for detailed studies of far-north
porcupines. She found none. With advice from biologists she respects, she
set up her own study, installing radio collars on porcupines in the forests
of Anchorage and with the help of her husband building pens for a few in
Fairbanks. The captive porcupines helped her understand how they functioned
on such a poor diet.
After a study that took her more than six years, Coltrane presented these
porcupine insights during her thesis defense:

* Alaska porcupines are almost twice as large as Lower 48 porcupines.

* Porcupines in her study area didn't "hibernate on the hoof" by lowering
their body temperatures to save energy; whether it was 30 above or 30 below,
porcupines ‹ insulated by their quills and dense guard hairs ‹ remained at
about the same body temperature as a human's.

* The porcupines in her study, each of which she named, ate a highly toxic
winter diet that required lots of energy to process. They survived the
winter by burning body fat and moving very little.

* Fifty percent of a porcupine's weight in fall was in the form of fat.
"That¹s ridiculously fat," Coltrane said. "Like a polar bear or a seal."

* Despite eating low-protein foods in winter, porcupines did not lose lean
tissue. They instead lost 30 percent of their fat reserves.

* More than 20 percent of their meager dietary intake was lost in their
urine, most likely a result of ridding their bodies of toxins stored in
spruce needles. 

* Her Alaska porcupines had larger winter home ranges than did Lower 48
porcupines, and spent time in mixed hardwood and conifer forests.
* Porcupines she studied spent 79 percent of their time in and around white
spruce trees, the rest of the time in birch. "(Eating) birch gives them a
break from the toxins," Coltrane said. "Maybe that¹s why they prefer mixed

* After dealing with winter "for a ridiculous number of months," Coltrane's
porcupines depleted their fat reserves. To survive, porcupines depend on
nutritious springtime greenery, which must be indescribably delicious after
months of nibbling bark and spruce needles.
This column is provided as a public service by the Geophysical Institute,
University of Alaska Fairbanks, in cooperation with the UAF research
community. Ned Rozell is a science writer at the institute.
Edit Module

Add your comment: