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A Tale of Two Squirrels Notecard



This is a story about two similar but unique squirrels. Although they appear together in this artwork these two squirrels are never seen together. The Abert squirrel (Scuirus aberti), pictured on the left, ranges throughout isolated mountainous areas in Arizona, New Mexico, Utah and Colorado. The Kaibab squirrel, shown on the right and named for the Kaibab Plateau, only occurs on the North Rim of the Grand Canyon. The Kaibab squirrel is classified by some as Scuirus kaibabensis, a distinct species, whereas some view it as a subspecies of the Abert squirrel.

How the squirrels became isolated is not clearly understood. What is thought is that some 10,000 years ago a species of Tassel-eared squirrel inhabited the forests of the American Southwest. As the Kaibab Plateau rose on the North Rim of the Grand Canyon the squirrels became geographically isolated from those on the South Rim. The Kaibab squirrel was cut off from its ancestral population by the Grand Canyon to the south and treeless deserts to the east, north and west. Separated they evolved distinctive characteristics. The Kaibab squirrel provides us with a rare look at how geographical isolation affects an animal’s development. The few miles that separates the Kaibab and Abert squirrels can be measured in thousands of years of evolution.

These squirrels both have tasseled ears which are covered by stiff hairs that stick straight up, making their ears appear almost twice as tall. Tassel-eared squirrels’ livelihood is intimately connected to the Ponderosa Pine for food and shelter. These shy, tree-dwelling squirrels serve an important role in the health of Ponderosa forests.

Ponderosa Pines have a symbiotic association with a specialized fungus interwoven with its roots. This fungus absorbs water and minerals from the soil and produces growth stimulants, all utilized by the trees; the pine in turn provides sugars for itself and the fungus via photosynthesis, a mutually beneficial trade-off. The fungus produces underground fruiting bodies called false truffles which are thoroughly enjoyed by the tassel-eared squirrels, who subsequently help spread fungal spores throughout the forest as they defecate.

artwork by Amelia Hansen ©2005
text by Steve Sierigk