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Wednesday, March 16, 2011

The Pine Bough Mystery

Why are all these pine boughs on the ground? Are the trees losing their needles?  Virginia, a local resident, hikes the Falls Trail to the Rio Grande every Sunday. On her outings she began to notice the path littered with the branch tips of ponderosa pines and junipers. We stopped to chat about mid-way down the trail. I told Virginia she was not the first visitor curious about this phenomenon. All week long adults and kids alike have been asking for an explanation. The other common question I have been asked is, “What is that animal with long ears that hops like a rabbit?” The answer to the latter question directly relates to Virginia' mystery . The animal responsible for the litter and strange appearance is a squirrel. With a back of charcoal gray, a bottle brush tail and two inch long tassel ears, long rear paws and strong hind legs, the Abert’s squirrel is readily distinguished from other squirrels.

There are nine sub-species of the tassel-eared squirrels in the Southwest. Their range extends from the mountainous Ponderosa pine forests of New Mexico, Colorado, Utah, Arizona and parts of Wyoming and north central Mexico. Subspecies of Sciurus aberti can be determined by cranial size, body weight and coloration. For example, S. aberti ferreus living in the foothills of Boulder Colorado has a jet black body and a vivid black topped tail while the tassel eared squirrel residing along the North rim of the Grand canyon, S. aberti kaibabensis, sports a tail the color of snow.

The nutritious pine cambium is one of the Abert’s squirrel’s primary food sources. Each subspecies has adapted to eating the inner bark or cambium of the ponderosa in the region where they live, finding the terpene composition from other pine populations unpalatable. Abert’s squirrels also dine on the ponderosa seeds and buds. Ponderosa pines begin producing seeds at about sixteen years and continue producing viable seeds until they are 350 years old. Each cone will produce about seventy-five seeds with an average mature tree producing two hundred cones in a good year. A single squirrel can feast its way through as many as seventy-five cones in a day.

Abert’s squirrels are active year-round. In autumn excess pine seeds along with acorns and fungi are cached for winter. When the snows are deep, the tassel-eared squirrel will spend much of its time confined to the crowns of the mature pines gorging on the cambium and sleeping in pine twig nests. In winter, it is common to see the ends of pine boughs, nipped by hungry squirrels, littering the trail.   

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