Ground squirrels are agile climbers on cliffs and among rocks as well as in fruit trees, live oaks, and other low trees, but I have never seen them far from the ground in large trees. When on the ground they run in a series of bounds like tree squirrels. The long, bushy tail is carried almost straight out behind when they scamper off in alarm, but at other times is curved and undulating, much as in the tree squirrels. They gather and manipulate food with their front paws, sitting upright on their haunches to eat or look about. On one occasion when I came to a foot-bridge over a broad irrigating ditch across which a number of ground squirrels were raiding an orchard, they did not hesitate to dash at full speed into the swiftly running water and swam quickly across to seek refuge in their holes on the far side. Like other spermophiles, the California ground squirrels hibernate for months in the cold, snow-covered parts of their winter range, but remain active throughout the year in the warmer areas, where no snow falls. Throughout their range they gather stores of seeds, grain, and acorns and other nuts, carrying them in their cheek pouches to underground store-rooms for use in bad weather. In the valleys of California they lie hidden in their burrows for days at a time during cold winter rains, but are out as soon as the sun reappears. One or more litters, each containing from six to twelve young, are born from March to late in summer, according to the locality. The young leave the nest and care for themselves when about half grown. The swarming abundance of the California ground squirrel on foothill slopes and in fertile valley bottoms equals the congregations of prairie-dogs in their most populous districts. This abundance of small animal life supports a great variety of predatory species, as coyotes, foxes, bobcats, several kinds of hawks, and the golden eagle. Owing to its predilection for ground squirrels, the golden eagle is protected by law in California, where many of them build their nests in low live oaks only a few yards from the ground. When house rats brought the bubonic plague to San Francisco a few years ago they also carried it across the bay and passed it on to the ground squirrels living in the foothills back of Oakland. Thence the disease spread among these animals through parts of several surrounding counties. The United States Public Health Service and the local authorities in a vigorous campaign stopped the spread of this malady, but not until the potential ability of these rodents as plague-carriers had been well established. This fact and the wide distribution of the California and other ground squirrels over a large part of the continent should not be overlooked in connection with possible future outbreaks of the plague. Fortunately, investigation and field experiments on a large scale have shown that these spermophiles may be destroyed by poison over great areas at a relatively small cost.