Survivability:

Belding’s ground squirrel faces many extreme pressures, especially the males. While females typically live four to ten years (the oldest reported female was eleven!) males only live three to six years (the oldest reported male was six) (Sherman and Morton 1979). This sexual dimorphism in the population is mostly likely caused by male dispersion and competition for mates, which puts them at higher risk for predation. The life expectancy for males is significantly less about the time that males begin to compete for mates. During fights, males kill each other by severing blood vessels in the neck, and often other injuries can become infected. Male-male fights occur in the open, so the fighting males are more vulnerable to predators (thus, to be able to mate, males participate in competitive behavior that could potentially shorten their life span). Males are also more mobile then females, and can be killed by cars or by predators in their travels. As a result, few males will live long enough to interact with their offspring, while females are much more likely to interact with their kin (Sherman and Morton 1979).

Selection Pressures:

Because of its relatively small size, S. beldingi has numerous predators. At Tioga Pass in California, Sherman and Martin found that predators kill 4% to 11% of the population. Predators include bears, coyotes and badgers (the main predators of adults (Sherman and Morton 1984) who dig the squirrels out of their burrows), weasels (Sherman and Morton 1979), pine martins (Sherman and Morton 1984) Cooper's hawks, red -tailed hawks, peregrine falcons, prairie falcons, and Clark's nutcrackers (Sherman and Morton 1979), minks, dogs, Swainson’s hawks, great egrets, American Kestrel, northern harriers, harpier, ospreys, common ravens, rattlesnakes, and gopher snakes (Robinson 1980). Obviously, predation pressure is very high. Winter weather is also an extreme selection pressure, with 54-93% of juveniles and 23-68% of adults dying during hibernation. Storms after emergence and spring food shortage can also kill S. beldingi populations (Sherman and Morton 1979).

S. beldingi usually responds to predators by giving an alarm call and by trying to increase its visual range by posting, fleeing, or approaching the predator. The snakes and the crane are mainly ignored, but all other predators elicit a response. S. beldingi ignore harmless terrestrial animals, showing that S. beldingi are also able to distinguish between harmful and harmless terrestrial animals. In every encounter with terrestrial predators, S. beldingi trill and often they run to their burrows. Occasionally S. beldingi will attempt to confuse the predator by running away and then doubling back (which is only occasionally successful). Interestingly, squirrels will occasionally chase weasels (Sherman 1985, Turner 1973, Robinson 1980)!

Alarm Calls!

S. beldingi has two specific alarm calls that it gives in response to predators. The first, called the churr call or the trill, is a series of more than five notes given rapidly (Robinson 1980). The trill is given in response to slow-moving predators (usually terrestrial animals) and other predators that pose a less immediate threat (Mateo 1996). Such predators include coyotes, badgers, weasels, livestock, humans, and cars (Turner 1973). Only the individuals that are close to a squirrel giving a trill call respond by posting (standing on back legs), by running to a rock to get a better view of the predator (Mateo 1996, Sherman 1977) or by returning to their own core areas, bypassing one-entrance burrows (Turner 1973). Churr calls are only in response to less serious situations. The other call given by S. beldingi is called the whistle. The whistle is a single high-pitched note that is given in response to the fast-moving, aerial predators or predators that are an immediate threat (Mateo 1996). All squirrels within hearing immediately respond to the whistle call by showing evasive behavior such as crouching (Mateo 1996) and fleeing to the nearest shelter, regardless of the number of entrances (Turner 1973). When aerial predators are spotted, fleeing squirrels call while escaping. In contrast, when terrestrial predators are spotted, squirrels flee to safety, and then call. All animals are equally likely to call in response to aerial predators, but females with kin are more likely to call in response to terrestrial predators. In addition, squirrels that are farthest from shelter seemed to be the first to call (Sherman 1985).The squirrel that is sounding the alarm does not try to hide itself, but sits straight up while calling and looks towards the predator (Sherman 1977).

What is so good about these alarm calls?

The alarm calls of S. beldingi are carefully tailored to inform others about the type of predator, and to communicate the seriousness of the situation. As mentioned above, trills are specifically given in response to potentially dangerous situations, such as terrestrial predators, while whistles are given in response to immediate danger, such as aerial predators. This behavior is highly adaptive, because S. beldingi are able to modify their reactions based on the risk of the situation. Interestingly, S. beldingi are also able to discriminate between harmful and harmless situations. For example, S. beldingi will not alarm call at a bird that is not a predator species and will alarm call less if a potential predator is flying far away from the colony than if it is flying directly over the colony (Robinson 1980). This saves the squirrels the time and energy that would have gone into responding to false alarms. In addition, though calling would logically draw the predator's attention to the caller, Paul Sherman determined that individuals that give an alarm call are more likely to escape from birds of prey. In addition, squirrels that are alerted are less likely to be caught (Sherman 1985). Thus, alarm calling is beneficial for both the caller and the responder.

The alarm calls given by S. beldingi have drawn the attention of many scientists nation-wide and are extensively studied for two reasons. First, the ability of juveniles to respond to alarm calls is crucial to their survival, and the development of this response can be studied relatively easily. Second, alarm calls are given most by female S. beldingi that have living relatives near by, suggesting that the alarm calls are altruistic (Sherman 1985).

Juvenile development of alarm call responses:

For S. beldingi, the first few months of life are inarguably the most dangerous. Small and unaware, juveniles could easily become dinner if they did not quickly develop the predator defense responses shown by their parents. As a result, S. beldingi have evolved so that the juveniles develop responses to alarm calls at an extremely early age. In fact, upon emergence from their natal burrow, the juvenile are immediately able to respond to alarm calls and objects that fly overhead (Mateo 1996). Despite this basic recognition, juveniles cannot distinguish between different calls, do not always respond correctly to alarm calls, and often respond to noises that are not alarm calls at all, such as juvenile squeals and wren calls (Mateo 1996). During the first five days above ground, juveniles will respond to alarm calls (except whistles) by freezing or going into a burrow. Older juveniles (at least 16 days), on the other hand, will respond to alarm calls by running to a burrow or posting, and only freeze in response to non-alarm calls (Mateo 1996). The responses of the older juveniles are much shorter lived, and the time spent alert after a calls decreases as the squirrel matures (Mateo 1996).

Interestingly, according to Jill Mateo, age is not the only factor that affects juveniles' responses to alarm calls. For example, juveniles are more likely to respond vigilantly to alarm calls early after their emergence if their dam is present (thought this effect only lasts five days after emergence). The presence of the dam is also positively correlated with the amount of time young remain alert after an alarm call. This correlation lasts up to twenty-five days after the young emerge (The influence of the dams on the response of the young may decrease because dams move farther away from the natal burrows as the young grow older). This may occur because the mother (dam) will chase her young back into the burrow when she sounds alarm calls to train them how to respond to the call (Turner 1972). Additional factors that decrease juveniles' responsiveness to alarm calls include visual isolation and location of their burrow at the center of the meadow. These factors most likely decrease responsiveness because the responses of adult S. beldingi serve as examples of correct behavior for the juveniles. If adults are not visible as models, or dams are less vigilant in the defense of their burrows (if they are in the middle of the meadow where predators are less prevalent) than the juveniles will not have adult examples to imitate. In addition, a juvenile's distance from its burrow increases its response duration and vigilance but has no affect on its likelihood to respond to the alarm call. In all, juvenile ground squirrels develop a complete set of differential responses to alarm calls by the end of their juvenile summer

, with or without the factors that affect the speed of this development (Mateo 1996).

Altruistic Alarm Calling:

Belding's ground squirrels have been used in many altruism studies because of their alarm calls. Specifically, they will call to warn their relatives of the approach of a predator, increasing their fitness by assisting their relatives. Adult and one-year-old female Belding's ground squirrels are much more likely to give alarm calls than males (who disperse away from their kin), and female squirrels with nearby kin are more likely to give alarm calls than those without living kin nearby. In addition, the chance that females will give alarm calls increases with age (Sherman 1977).