Many prey animals like rodents, birds, and primates use alarm or warning calls to alert others in their group about potential predators. But how exactly do these warning calls help prey adapt and improve their chances of survival?
If you’re short on time, here’s a quick answer: Warning calls allow prey animals to take evasive action, while also signaling to predators that they have been detected, which can deter attacks. In this article, we’ll explore the fascinating adaptations prey species have evolved to effectively use alarm calls for survival.
In this comprehensive guide, we’ll discuss the various purposes of warning calls for prey species and how specific adaptations like syntax, semantics, vocal learning, and call combinations provide survival benefits.
We’ll also look at some examples of sophisticated warning call systems among animals like prairie dogs, chickens, and primates to understand how these alarm calls are produced and interpreted.
The Purposes and Benefits of Alarm Calls
Quickly Alerting Others in the Group
When prey animals like meerkats or prairie dogs detect a predator, they rapidly emit loud alarm calls to quickly inform other members of their group about the threat (Klump & Shalter, 1984). These alarm calls act as an early warning system to alert as many individuals as possible so they can take evasive action.
The alarm calls are loud, high-pitched sounds that immediately grab attention. Researchers have found that the speed of spreading alarm calls can enable an entire meerkat colony to disappear into their burrows within just a few seconds (Townsend, Hollén, & Manser, 2010).
This rapid response time is vital for survival.
Signaling Awareness to Predators
Some evidence suggests prey animals issue alarm calls not only to warn group-mates, but also to signal awareness to predators. For example, certain primate species will routinely emit alarm calls in response to predators even when no other group members are present in the vicinity.
Researchers speculate that by vocalizing in these one-on-one encounters, the prey animals inform the predator “I’ve spotted you, you lost the element of surprise” (Fichtel & Manser, 2019). This may sometimes deter predation attempts, as some predators rely on stealth and the unawareness of their prey.
Encoding Information About Threats
The alarm calls of some species, like prairie dogs, can encode complex information about threats such as the predator type, size, speed of approach and level of danger (Slobodchikoff et al., 2009). Different calls are elicited by coyotes, domestic dogs and hawks for example.
And within each threat category, factors like the predator’s proximity and trajectory can also be distinguished in the alarm calls. This means nearby prairie dogs can glean rich information about imminent dangers simply by listening to the calls.
The specific information conveyed enables receivers to select situation-appropriate anti-predator responses – prairie dogs react faster and are more likely to dive into burrows upon hearing high urgency calls elicited by rapidly approaching predators (Sloan et al., 2005).
Allowing Receivers to Take Evasive Action
Alarm calls allow receivers to take immediate evasive action, such as fleeing to a refuge or hiding spot. Gazelles and impalas that hear calls indicating an ambush predator is lurking may rapidly flee the vicinity or quickly move to scanning positions where they can detect threats more easily (Lea et al., 2008; Skelhorn, 2011).
Primates hearing aerial predator calls tend to immediately dash into dense vegetation for cover or camouflage and freeze in place (Fichtel & Manser, 2019). And ground squirrels are prompted by calls to quickly stand upright and assess risks or rapidly dive into their burrow openings if danger seems imminent (Swan & Hare, 2008; Sloan et al., 2005).
Taking fast evasive responses enhances prey survival. Alarm calls provide the critical information needed to appropriately react.
Alarm Call Adaptations in Prey Species
Syntax: Structural adaptations in call types
Prey species like vervet monkeys and prairie dogs have evolved specialized alarm calls to warn others about specific threats (1). These calls have distinct acoustic structures based on the type of predator, such as elongated calls for aerial predators and abrupt, pulsed calls for terrestrial predators (2).
The different syntaxes allow other members of the group to respond appropriately without directly observing the threat. For example, vervet monkeys will run into trees after hearing an eagle alarm but look down for snakes after a snake alarm call (3).
Thus, structural adaptations in alarm call syntax provide a survival advantage by enhancing comprehension of the danger. This syntax-based alarm call system requires sophisticated vocal control and acts as an early warning system to promote vigilance against different predators.
Semantics: Encoding threat details
Beyond just predator type, some prey species can encode detailed semantic information about threats in their alarm calls. Suricates, a species of African mongoose, have over 10 different alarm call types forpredators, with variations in call elements based on features like predator distance, size, and direction of travel (4).
Ground squirrels similarly modify their calls to indicate the predator’s proximity (5). This ability to embed meaning about relevant threat details allows receivers to make better decisions on how to take cover or mob the predator.
It requires advanced call production learning and comprehension skills. The increased specificity expands the information conveyed in alarm calls, enhancing their value for survival.
Vocal learning: Flexibility in call usage
A key adaptation in some prey species is vocal learning, which allows greater flexibility in alarm call usage. For example, wild banded mongooses have shown the ability to learn new predator alarm calls from other groups when they join the group (6).
Dwarf mongooses even learn alarm calls for novel predators from other species, such as hornbills (7). This social transmission through vocal learning enables mongooses to develop appropriate escape responses to new dangers in their environment.
In contrast, species like vervet monkeys with fixed alarm call repertoires may struggle to adapt their warnings to novel threats. Thus, vocal learning provides benefits in alarm call flexibility and communication between groups.
Combinations: Conveying complex meanings
More advanced prey species combine call elements to convey complex, multidimensional meanings that provide better information to conspecifics.
Chestnut-crowned babblers in Australia have threat-specific alarm calls but can modify meaning by adding suffixes, allowing information like level of threat urgency or predator behavior to be encoded (8).
Similarly, Diana monkeys combine their leopard and eagle alarm calls to recruit group members for defense (9). This combinatorial syntax expands the semantic information and requires sophisticated cognition to comprehend meanings.
It allows prey animals to provide detailed updates on dangers, enabling threat-specific strategic responses for improved survival outcomes.
Examples of Sophisticated Alarm Call Systems
Prairie dogs: Descriptive calls about predators
Prairie dogs have one of the most sophisticated alarm call systems of any animal. They can describe specific predators such as hawks, coyotes and humans through different vocalizations, indicating the type of predator, how far away it is, and how much danger it poses (Slobodchikoff et al. 1991).
Prairie dogs even have specific alarm calls for humans holding guns versus just standing upright (Slobodchikoff et al. 2009).
Researchers have identified distinct vocal elements that classify predators by size, color, and speed of movement. By combining these elements in various ways, prairie dogs can construct composite alarm calls that contain detailed information about the predator (Frederiksen & Slobodchikoff 2007).
Prairie dogs are able to convey this complex information through syntax, or meaningful combinations of distinct vocal elements. Their alarm calls demonstrate semantics, or encoding of meaning, as well as some basic language processing abilities like generalization of concepts (Slobodchikoff 2012).
Chickens: Food and aerial alarm call syntax
Studies on fowl like chickens have revealed alarm call systems with syntactic complexity. Chicken food calls are composed of distinct note types assembled in different arrangements that alter meaning (Evans & Evans 1999).
For example, a sequence of high-low notes indicates a preferred food source like corn, while a string of repeated low notes indicates a less palatable food like wheat. Chickens combine notes in meaningful sequences like humans construct sentences out of words (Evans & Evans 2007).
Chickens also have aerially-specific alarm calls for flying predators made up of different note types, intensities, and patterns. They are able to signify the size, distance, and threat level of raptors like hawks through call syntax (Evans et al. 1993).
Primates: Semantics and combinations in calls
A number of non-human primates also have sophisticated vocal communication systems. Vervet monkeys produce acoustically distinct alarm calls for specific predators like eagles, snakes and leopards (Seyfarth et al. 1980).
Their calls are meaningful – other monkeys that hear them respond appropriately by looking up, peering down, or scrambling up trees even without seeing the actual threat.
Other primates like Putty-nosed monkeys combine calls into sequences with different meanings. “Pyow” calls function as general alerts while “hack” calls indicate movement, but the sequence “pyow-hack” recruits the group for travel to a new location (Arnold & Zuberbühler 2006).
Combining existing calls in new ways allows greater communication flexibility.
Some primates are even capable of rudimentary grammar, like Campbell’s monkeys that alter call meaning by affixing certain notes to the beginning or end of statements (Ouattara et al. 2009). This demonstrates the ability to construct new call variants using meaningful sound units and grammatical rules.
Conclusion
In conclusion, warning calls are an essential adaptation that provide prey species with a key survival advantage against predators. The ability to quickly alert others, signal awareness, and provoke evasive maneuvers is critical for prey animals’ fitness.
Remarkably, many species have evolved complex structural and semantic alarm call adaptations that allow for very informative communications about threats. Understanding how animals leverage these warning systems can provide fascinating insights into evolution, animal cognition, and communication.
