Alarm Call Creates Confusion
KeywordsGround Squirrel Personal Risk Alarm Call Mammalian Predator Terrestrial Predation
Alarm calls may signal the presence of a predator, creating confusion and reducing the threat of predation.
Group living increases the likelihood that predators will be detected through cooperative vigilance. This social structure is particularly beneficial if individuals can alert others to potential threats as soon as these are detected. Hence, alarm calls are evident in a numerous group living species across a range of taxa including fish, birds, and mammals (e.g., Bessey and Heithaus 2013). These alarm calls may convey a range of important information such as predator type or location through varying the number or rate of calls, amending the intensity or volume of call, or generating calls that are qualitatively different (Zuberbuhler 2000). It has been suggested that those signaling the presence of a predator may be at increased risk of detection by predators. The present entry outlines the manner in which alarm calling may impact on group behavior, create confusion, and hence reduce the likelihood of predation.
A range of theories have been proposed to explain the tendency to produce alarm calls which may draw attention to the caller, delay escape, and increase the personal risk of detection and capture for the caller. In particular, these calls may deter predators, startle predators leading to the release of captured prey, encourage others to seek cover, or attract individuals to the vicinity in order to defend vulnerable group members (Goedert et al. 2014). It has been suggested that producing an alarm call may not increase the individual risk of predation. For example, calls providing an honest signal of caller quality may reduce the likelihood that the individual is targeted by predators or alarm calls may signal to the predator that it has been detected, encouraging the predator to abandon the attack (Bergstrom and Lachmann 2001; Laiolo et al. 2007). Similarly, alarm calls may contain a range of features which reduce the conspicuousness of the signaler. Hence, calls may be difficult for predators to localize or ventriloquial (Wood et al. 2000).
Alarm calls may also create a confusion effect which reduces the likelihood of successful attack (Cresswell 1994). This confusion may result from the number of individuals seeking cover and vocalizing or from the presence of additional predators and heterospecifics attracted by the alarm calls and increased activity (Chu 2001). Solitary prey may be quickly captured though many unsuccessful attempts are often required for predators to capture a member of a group living species. Hence, the confusion effect makes it difficult for predators to identify, track, and attack single members of a group and leads to a greater number of attacks required per kill (Curio 1976). It is of course important to consider the form and function of alarm calls separately for each prey and predator type.
For example, Belding’s ground squirrels (Spermophilus beldingi) produce distinct alarm calls in the presence of mammalian terrestrial (multiple note trills) and avian aerial (single note whistles) predators. Squirrels producing trills are more vulnerable to terrestrial predation, and mammalian predators appear attracted to those producing these calls. Therefore, alarm calls (trills) produced in response to mammalian predators appear to be a form of kin focused protection. In contrast, aerial predators (raptors) rarely capture squirrels after an alarm call has been produced, and alarm callers are less likely than noncallers to be killed (Sherman 1985). Those most likely to produce the calls were close to the predator and further from cover. Hence, the production of single note whistles in response to aerial predators appears to reduce the likelihood of personal risk of predation.
In some circumstances, the increased activity among group members which follows alarm calling may confuse predators, leading to a reduced rather than increased threat of predation for alarm callers.