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One Of Continent's Rarest Animals Is Disappearing Because Of Suppression Of Natural Fires, Cornell Genetics Study Suggests

May 4, 1999
Cornell University
Cornell University biologists who study dwindling populations of one of the rarest mammals in North America have found another reason to let "natural" fires burn. Without lightning-sparked fires every 10 to 12 years, they say, pine trees are isolating Northern Idaho ground squirrels into shrinking groups where non-native plants that do not supply adequate food for the rodents have overwhelmed natural, fire-resistant, seed-laden grasses.

ITHACA, N.Y. -- Cornell University biologists who study dwindlingpopulations of one of the rarest mammals in North America have foundanother reason to let "natural" fires burn. Without lightning-sparkedfires every 10 to 12 years, they say, pine trees are isolating NorthernIdaho ground squirrels into shrinking groups where non-native plants thatdo not supply adequate food for the rodents have overwhelmed natural,fire-resistant, seed-laden grasses.

"Animals can run from fire, but they can't escape the disastrouseffects of habitat fragmentation and starvation. Unless these squirrelscan link up with neighboring populations and obtain sufficient fatty seedsto carry them through hibernation, I'm afraid they will die off altogetherin our lifetime," says Paul Sherman, one of four biologists authoring agenetic study of the Northern Idaho ground squirrel ("Spermophilus brunneusbrunneus") in the current "Journal of Mammalogy" (Vol. 80, No. 1, pp156-168).

Sherman, a Cornell professor of neurobiology and behavior, andcolleagues Thomas Gavin, Eric Yensen and Bernie May offer a two-partsolution for the squirrels' dilemma:

-- Restoration of habitat, including reopening of meadows, toreconnect squirrel populations.

-- Reintroduction of fire into the ecosystem to restore nativevegetational structure.

Fourteen years ago, when Yensen of Albertson College of Idaho beganthe squirrel study in the high-desert meadows of western Idaho, there wereabout 1,000 of the ground squirrels on public and private lands aroundPayette National Forest, the only part of North America where the rareanimals live. By 1998, the total population had shrunk to about 600, and12 of the 36 known populations were extinct, according to Gavin ofCornell's Department of Natural Resources.

The U.S. Fish and Wildlife Service has proposed listing "S. b.brunneus" as "threatened," deserving of protection through the EndangeredSpecies Act.

The Northern Idaho ground squirrel depends on the fat-rich seedsof native bunch grass to sustain it through seven or eight months ofhibernation. Before the federal government instituted a policy ofsuppressing wildfires early in the century, the meadows burned every 10-12years, and the heat-resistant bunch-grass seeds then regreened Idaho'smeadows.

But without natural fires to maintain the diversity of plant life,Gavin explains, a few non-native plant species took over. "The non-nativeplants put all their energy into rapid vegetative growth rather than makingnutritious seeds," he says. "As a result, the ground squirrels cannot findenough seeds to fatten sufficiently before their long hibernation, fromAugust to March."

Gavin adds, "To make matters worse, when squirrels try to migratein search of food or mates, their paths are blocked by dense stands of pinetrees that thrive in the absence of fire. This means that groups can nolonger mix when some populations expand and others drop because of disease,a hard winter or predators. Sometimes one hard winter and a little badluck with hawks, badgers and other predators are all it takes to wipe outan isolated, local population. They cannot be rescued by dispersers fromnearby populations that are doing well."

Cornell's long-term study of Idaho ground squirrels had, at first,focused on the animals' social behavior. But the focus changed asresearchers returned each spring to sites where small colonies had thrivedthe year before -- only to find no animals emerging from their winterburrows. Analysis of blood proteins and DNA from surviving squirrelsoffered three clues:

-- Ground squirrels in isolated populations are slightlydifferentiated in their genetic makeup, suggesting that they probablyintermingled earlier in the century, before dense conifer forests closedin, but that intermixing no longer occurs.

-- Squirrel populations as close as two miles apart are no longermixing.

-- The farther apart populations are geographically, the moredifferent they are genetically, suggesting that they have been separatedlonger, and that little or no dispersal is occurring between populationstoday.

The biologists' hypothesis -- that inadequate nutrition is onecause for the squirrels' disappearance -- received a boost from an"accidental experiment," when cattleman Frank Anderson moved to a remotehouse on the OX Ranch. Within a year, the Idaho ground squirrels aroundAnderson's residence were reproducing like rabbits and doubling theirweight during the summer months, just like hibernating animals are supposedto.

Sherman and Gavin quickly pinpointed the cause of the populationexplosion: Seed-starved squirrels were eating kibble the rancher leftoutdoors for his herding dogs, as well as spilled oats from horse feed.

Now the dog chow-fed squirrels are part of a deliberate experimentby the Idaho Department of Fish and Game, the U.S. Forest Service andresearchers from Cornell and Albertson College:

-- Controlled, "cool" fires are set to burn off non-nativevegetation and underbrush that blocks the ground squirrels' movement fromone population patch to others. Unlike hot, uncontrolled wildfires, thecontrolled burns should not destroy seeds of native plants, including somethat require heat to germinate.

-- Burned meadows are reseeded to reintroduce native plants thatthe ground squirrels and other wildlife need.

-- Healthy squirrels from the ranch house population are humanelytrapped and moved to prepared sites in burned and reseeded meadows. Thebiologists even dig burrows with power augers, giving the squirrels a headstart in establishing new homes.

"It's not Purina dog chow, but they're finally getting plenty ofthe leaves and fat-rich seeds of native grasses that they've been missing,"said Gavin. He credits students in the conservation biology course heteaches at Cornell for highlighting the role of nutrition in squirrelpopulation problem.

Gavin said that controlled "cool" fires are not a threat to groundsquirrels, which are safely hibernating several feet underground whencontrolled fires are set.

"We know this runs counter to everything Smoky the Bear taught us,"Sherman said. "But we think Smoky was worried about careless campers andcigarettes, not the natural fires that are set by lightning. Ironically,we've become so good at fire suppression that many forests are tinder boxesof underbrush and non-native vegetation. Now, when a fire gets out ofcontrol it really is a threat to wildlife.

"The Idaho ground squirrels are part of an ecosystem thatfunctioned successfully for tens of thousands of years, and natural fireswere a part of that system, too," Sherman said. "Perhaps by undoing some ofmankind's tampering -- as well-meaning as it was -- and setting back theclock, we can encourage the re-establishment of native flora and fauna,especially the rodent variety, while saving the immense costs of fightingcatastrophic fires every summer."

Authors of the "Journal of Mammalogy" report, "Population GeneticStructure of the Northern Idaho Ground Squirrel," are Gavin, Sherman,Yensen and May, formerly a research associate in Cornell's Department ofNatural Resources and now a researcher in the Department of Animal Scienceat University of California at Davis. The genetics study was supported, inpart, by the National Science Foundation, U.S. Department of Agriculture,National Geographic Society, Idaho Department of Fish and Game and the OXRanch.

Related World Wide Web sites: The following sites provideadditional information on this news release. Some might not be part of theCornell University community, and Cornell has no control over their contentor availability.

-- Idaho Department of Fish andGame:

-- U.S. Fish and Wildlife Service - endangered speciesinformation:

-- OX Ranch:

-- Cornell Department of Natural Resources:

-- Cornell Section of Neurobiology and Behavior:

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The above post is reprinted from materials provided by Cornell University. Note: Materials may be edited for content and length.

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Cornell University. "One Of Continent's Rarest Animals Is Disappearing Because Of Suppression Of Natural Fires, Cornell Genetics Study Suggests." ScienceDaily. ScienceDaily, 4 May 1999. <>.
Cornell University. (1999, May 4). One Of Continent's Rarest Animals Is Disappearing Because Of Suppression Of Natural Fires, Cornell Genetics Study Suggests. ScienceDaily. Retrieved June 30, 2015 from
Cornell University. "One Of Continent's Rarest Animals Is Disappearing Because Of Suppression Of Natural Fires, Cornell Genetics Study Suggests." ScienceDaily. (accessed June 30, 2015).

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