use they work (p. 137).
Researchers have for years believed that animal alarm calls may be altruistic in nature, but this is a difficult concept to measure, as it supposes behavior benefitting relatives or the community, while at the same time putting the alarm-giver at risk of losing its life (Milius, 1998, p. 174). This theory is very difficult to test in wild animals because it requires observing a group of wild animals with one or more responding to a threat by giving an alarm signal, and then being able to observe the actions of other identified relatives or community members, and the alarm giver, to determine the outcome. It is almost impossible to determine who are relatives in many wild species, unless a family has been studied intensely and relatives marked for recognition.
The Belding ground squirrel is a gregarious creature that lives in open country with little forest cover (Budiansky, 1998, p. 131). It digs burrows, but spends much of its time in the open on rocks and logs, so is very vulnerable to attack by birds of prey and ground predators such as badgers. The squirrel produces two different types of alarm signals: a high-pitched whistle of a single, pure tone if the predator is airborne, and a rough chattering if the predator is on the ground (p. 132). The source of a high-pitched, pure tone is very hard for mammals or birds to locate in space, so the squirrel is not giving away its location by giving this call. The call also causes a mad rush for cover by other squirrels and thus confuses the predator (p. 134). Squirrels that make a shrill whistle when they see a hawk tend to survive and pass on this trait, and squirrels that run for cover when they hear this alarm call also survive to pass on their traits, so the alarm call has sheer survival value (Budiansky, 1998).
Milius cites a landmark study by Paul W. Sherman of Cornell University of alarm calls in Belding's ground squirrels (p. 174). Sh...