closely together in colonies, and individuals give audible alarm calls when possible predators approach. Recent research has shown that in some cases, ultrasonic alarm calls are given, and are responded to by other members of the colony. Richardson's ground squirrels use two audible alarm calls, a high-pitched whistle and a 'chirp' call. The whistle is given in response to terrestrial predators, while the chirp is given in response to aerial predators such as hawks. Predators include hawks, owls, snakes, weasels, badgers and coyotes. Feeding These animals are omnivores, eating seeds, nuts, grains, grasses and insects. In addition they have cannibalistic tendencies, where they will consume the corpses of other ground squirrels after dragging them down their burrows or indeed on the surface. Hibernation Adult ground squirrels may hibernate as early as July, though in their first year, the young ground squirrels do not hibernate until September. The males emerge from hibernation in March, and establish territories before the females emerge a couple of weeks later. Abandoned burrows are sometimes taken over by other grassland species such as the burrowing owl. Reproduction Female Richardson's ground squirrels produce one litter per year. Litter size averages 6, though the maximum size recorded is 14. The young are born in April or May. Young ground squirrels remain underground in the burrow until they are approximately 30 days old, emerging from natal burrows late May to mid-June. At emergence, the young weigh 50 to 100 grams. Relationship with humans Because they will readily eat crop species, Richardson's ground squirrels are sometimes considered to be agricultural pests, although this is not their legal status in all jurisdictions. The government of Saskatchewan declared the animals pests in 2010, allowing local governments to employ gopher control measures. In areas with few natural predators, overpopulation and increasing density can drive ground squirrels to expand into suburban neighborhoods. Control measures Farmers and ranchers have developed a variety of ways to exterminate ground squirrels besides trapping, shooting and poisoning. One such process fills the burrows with a mixture of oxygen and propane and then ignites the gas mixture. This kills the ground squirrels with a concussive force that also collapses the tunnel systems. Even if effective, ground squirrels from outside of the treated areas will eventually spread back into the area. The Saskatoon Wildlife Federation sponsored a 12-week "gopher derby" in 2002, in an effort to reduce what it considered an