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The ability to detect an incoming attack provides a final opportunity for an animal to avoid predation. In birds, vision is the main sensory mode in detecting attacks, but auditory cues likely play an important role. The role of auditory cues from predators themselves remains largely unstudied. We evaluated the ability of free-living, gregarious sparrows (Passerellidae) to recognize attacks based on the non-vocal sounds made by predators or indirect auditory cues of ongoing attacks, mainly in the form of brief wingbeat sequences from predatory and non-predatory birds. Behavioral responses to playbacks were video-recorded and expressed in terms of a flock's propensity to respond, either by flushing to cover, becoming vigilant, or both. Sparrows responded equally to hawk wingbeats and those of small passerines. Both predator and non-predator wingbeat sequences induced anti-predator responses, especially when played loudly. Loud control sounds, such as hammering, induced few responses. Birds also responded to the sounds of a walking and running terrestrial predator (a dog), but reactions to the walking predator often involved birds jumping onto objects for a better view of their surroundings rather than immediate flight to cover. In an additional experiment, we examined how characteristics of wingbeat sequences (i.e., the number and cadence of hawk wingbeats) affected passerine responses. It indicated that only two consecutive hawk wingbeats, presented at a natural cadence, are necessary to elicit a strong response to a playback. Single hawk wingbeats induced only weak escape responses, as did artificially slowed cadences. Birds in general likely possess the ability to recognize non-vocal, auditory cues of incoming attacks, which may be produced by approaching threats or departing congeners. [ABSTRACT FROM AUTHOR]

Socio-demographic factors, such as group size and their effect on predation vulnerability, have, in addition to intrinsic factors, dominated as explanations when attempting to understand animal vigilance behaviour. It is generally assumed that animals evaluate these external factors visually; however, many socially foraging species adopt a foraging technique that directly compromises the visual system. In these instances, such species may instead rely more on the acoustical medium to assess their relative risk and guide their subsequent anti-predator behaviour. We addressed this question in the socially foraging meerkat ( Suricata suricatta). Meerkats forage with their head down, but at the same time frequently produce close calls ('Foraging' close calls). Close calls are also produced just after an individual has briefly scanned the surrounding environment for predators ('Guarding' close calls). Here, we firstly show that these Guarding and Foraging close call variants are in fact acoustically distinct and secondly subjects are less vigilant (in terms of frequency and time) when exposed to Guarding close call playbacks than when they hear Foraging close calls. We argue that this is the first evidence for socially foraging animals using the information encoded within calls, the main adaptive function of which is unrelated to immediate predator encounters, to coordinate their vigilance behaviour. In addition, these results provide new insights into the potential cognitive mechanisms underlying anti-predator behaviour and suggest meerkats may be capable of signalling to group members the 'absence' of predatory threat. If we are to fully understand the complexities underlying the coordination of animal anti-predator behaviour, we encourage future studies to take these additional auditory and cognitive dimensions into account. [ABSTRACT FROM AUTHOR]

Animals can reduce their uncertainty of predation risk by attuning to antipredator behavior of others or assessing the risk for themselves. Although it has never been empirically examined in the context of predation, we predicted that animals combine information gleaned from others with their own sampling experience to estimate risk. To test this prediction, we assessed the state-dependent mobbing responses of migrant and resident songbirds at a fall migration stopover site in eastern Canada to stimuli simulating a range of predation risk situations. We presented individuals with social cues in the form of playbacks of black-capped chickadee (Poecile atricapillus) mob-calls conveying graded information about predator size in combination with a predator model (one of two owl species) that rendered the social information either correct or incorrect. The response did not differ based on migratory state; both migrant and resident birds stayed longer at experimental trials when presented with erroneous social information. In particular, response duration of birds presented with a low-threat chickadee mob-call and a high-threat model (understating the risk) was substantially longer than the response to other low-threat call trials, suggesting that individuals were capable of Bayesian updating by devaluing the social cue and acting on their own assessment. [ABSTRACT FROM PUBLISHER]

Migrating animals face numerous mortality risks, such as novel predators with which they may not be accustomed. Most animals can recognize predators innately; however, additional predator information can be collected to enhance familiarity. Because migrating birds rarely participate in mobs, they may seek alternative information sources such as cues provided by other birds that can provide information on predator location, identity, and degree of threat. We predicted that Nearctic–Neotropical migrants (hereafter, “migrants”) would react to vocal antipredator cues (e.g., mob-calls) of species residing in areas through which they migrate. To test this, we conducted experiments in Belize during spring migration, using playbacks of mob-calls of black-capped chickadees ( Poecile atricapillus) and blue-gray tanagers ( Thraupis episcopus); tanagers are familiar to all birds in Belize; chickadees are novel to residents but familiar to migrants. This also allowed us to assess response to novel and out-of-context antipredator signals. Resident birds did not respond to novel chickadee mob-calls, but did respond to familiar tanager calls. Birds overwintering south of our study area, which were migrating during our study, responded most strongly to chickadee playbacks. Conversely, individuals of species that include our study area in their winter range did not respond to either playback. This is the first evidence that birds react to vocal antipredator cues during migration, which may be a strategy used by migrants to learn about predators. Although residents failed to recognize a foreign cue, migrating birds responded most strongly to the out-of-context chickadee cue, associated with breeding grounds >2,000 km northward. [ABSTRACT FROM AUTHOR]