able to use vocalizations to warn conspecifics of the possible threat. This simple example demonstrates that flocks are not only seen in bird species or a herd of sheep, but it is also apparent in other animals such as rodents. This alarm call of the ground squirrel requires the ability of the animal to first recognize that there is danger present and then to react. This type of behaviour is also seen in some birds. It is important to note that by making an alarm call to signal members of the flock one is providing the predator with an acoustical cue to the location of a possible prey. The benefit here is if the members of the flock are genetically related to one another. If this is true, even if the bird that signalled the flock were to die its fitness would not decrease according to Hamilton's Rule. However another study involving thick-knees challenged whether or not an animal had to recognize the presence of a predator for protection against it. Thick-knees are birds that are seen in large flocks during particular seasons in various regions of the world. During the nonbreeding season, Peruvian thick-knees in Chile are reported to have an average of 22.5 birds — a mixture of adults and youngsters — in their flocks. Young birds were observed learning anti-predator behaviour strategies from adults during this time. Researchers believe that the flocking behaviour may help to decrease a predator's success rate when attacking the flock, rather than increasing the ability of the flock to spot an approaching predator. By birds co-existing with one another in a flock, less time and energy is spent searching for predators. This mutual protection of one another within the flock is one of the benefits to living within a group. However, as flock numbers increase the more aggressive individuals within the flock become towards one another. This is one of the costs to living within a flock. It is often seen that flocks are dynamic and thus fluctuate in size depending on the needs of individuals in order the maximize benefits without incurring a large amount of costs. By living in a large flock, birds are also able to attack the predator with a stronger force compared to if the bird was on its own. In the black-capped chickadees it can be seen that flocks of birds can produce a mobbing call