The average weight of six adult female Oregon Ground Squirrels was found to be 302 grams (about 10½ ounces). The full stomachs of these six squirrels were found to give an average weight of 18.5 grams. Subtracting the ascertained weight of the stomach itself (3.5 grams), gives the weight of the contents, alone, representing doubtless one full meal, as 15 grams, or one-twentieth the entire weight of the animal. The stomach contents was in all cases a closely packed, slightly moist (not watery) mass of finely chewed green stuff. This could not be analyzed as to kinds of plants represented, but the squirrels were seen to be feeding upon all sorts of vegetation, practically everything going to make up the usual forage grazed from such lands by live stock.
Our observations led us to believe that, at the very least, two full stomach-loads of greens were eaten by each squirrel each day, or 30 grams of forage. Of course this does not account for wastage, evidence of which, in the way of cut stems and grass blades, was plentiful. Figuring from the average number of adult squirrels per square mile, 70,000, and counting on two meals per day, we find a minimum of 2,100,000 grams, or somewhat more than two tons, of green forage devoured by the squirrels each day on a square mile of pasture. Granted that a grazing steer eats fifty pounds of pasture forage each day, we conclude that the squirrels on a square mile of pasture appropriate each day the forage which might support ninety head of cattle.
Expressing it in other ways, 750 Oregon Ground Squirrels during the growing season of pasture grass eat as much as one steer, and the squirrels on every seven acres of pasture thickly inhabited by them eat as much as one steer!
The burrows of the Oregon Ground Squirrel where the animals are at all numerous fairly riddle the ground. Most of the openings come to the surface at a rather steep angle and without any earth at their mouths. Now and then there is an opening which slants to the surface and has a good-sized mound, and such as these seem to mark the nesting burrows as distinguished from the short, temporary, refuge burrows, or those occupied by males. We spent the entire day of May 16 excavating one nesting burrow, with results shown in figure 19.
The mound at the main entrance to this burrow system was rather large in extent, though shallow. It consisted of this year's loosely piled earth, covering up the grass on an area of nearly two square yards and thus marking the place conspicuously. The system of burrows, in part at least, probably represented two seasons' work and maybe more. While there were only two openings to this system, there were several points at which underground branches came nearly to the surface so that a hard-pressed squirrel, pursued by some underground enemy, could have quickly dug clear out and escaped overland.
As usual with ground squirrels, the runways were everywhere smooth and free from excrement, the nest chamber in use being unexpectedly clean. The feces of the young are evidently collected by the mother and carried to the places where her own are deposited, in the special branches or defecatoria. Here the earth is tamped over the mass in such a way that the pellets are kept separated by the soil particles, with no chance to fester. The fecal pellets are dryish, anyway. Some saved for examination, probably from the adult squirrel, prove to be
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