Ravens adjust their antipredatory responses to con‐ and hetero‐specific alarms to the perceived threat

Abstract

Heterospecific alarm calls are typically found in situations where multiple species have a common predator. In birds, they are particularly common in mixed mixed‐species flocks. In species with highly developed social and cognitive abilities like corvids, there is the potential for differential responses to heterospecific vs. conspecific calls according to the riskiness of the habitat. We tested the responses of free‐ranging ravens (Corvus corax) to conspecific alarm calls and compared them to heterospecific alarm calls of jackdaws (Corvus monedula). We observed the proportion of ravens leaving the feeding site after the con‐ or hetero‐specific playback was presented in a situation of low threat (wild boar—Sus scrofa enclosure) and high threat of predation (wolf—Canis lupus enclosure). We show that ravens responded to conspecific calls more intensively at the wolves than at the wild boar, but the response to conspecific calls was in both enclosures stronger than to the control (great tit—Parus major song). The response to the heterospecific alarm was also stronger in the wolves’ enclosure, but it did not differ from control in the wild boar enclosure. These findings suggest that ravens are aware of the meaning of the jackdaw alarm calls, but they respond to it only in a situation of high predatory threat (wolves are present). In the wild boar enclosure, the ravens probably consider jackdaws warning against some other predator, very probably harmless to ravens. This interpretation requires further testing, as both enclosures differ also in respect to other parameters like food quality and shelter availability.

Decision time modulates social foraging success in wild common ravens, Corvus corax

“…For data collection, we chose the enclosure of wild boars Sus scrofa as the enclosure's landscape allowed an excellent view of the feeding site and its surroundings. Furthermore, compared to the feedings of large predators like wolves Canis lupus and bears Ursos arctos , wild boars do not show any aggressive food defence towards ravens (Bugnyar & Kotrschal, ; Nácarová, Veselý, & Bugnyar, ).…”

Who is crying wolf? Seasonal effect on antipredator response to age-specific alarm calls in common ravens, Corvus corax

“…Although ravens face severe foraging competition in winter (Heinrich, 1989) and may divide their attention between gaining access to food (B. Heinrich & Marzluff, 1995), fending off conspecific kleptoparasitism and cache pilferage (Bugnyar & Kotrschal, 2002;Gallego-Abenza, Loretto, & Bugnyar, 2020;Heinrich & Pepper, 1998), there are hardly any indications that competition for food affects their antipredator behaviour, at least not at our study site (Nácarová et al, 2018). Finally, the temporal pattern found might be considered an artefact of our testing.…”

“…Such assessment capability by receivers was also documented in small mammals, precisely in adult Richardson´s ground squirrels (Sloan & Hare, 2008). When confronted with alarm calls from conspecifics and closely related heterospecifics during foraging, carrion crows tended to respond to any alarm calls (Bílá, Beránková, Veselý, Bugnyar, & Schwab, 2017), whereas ravens adjusted their antipredator behaviour depending on the perceived risk (whether or not they snatched food from predators; Nácarová, Veselý, & Bugnyar, 2018) and the familiarity of the calling species (Davidkova, Veselý, Syrova, Nacarovà, & Bugnyar, 2020).…”

“…The groups are composed mostly of non-breeders in the first years of life (juveniles and subadults, < 4 years old) but also adults that do not hold a territory and/or visit this group in the non-breeding period opportunistically; they continuously change in composition with noticeable individual differences in terms of how long ravens stay and/or leave Loretto et al, 2017). We focused on the wild boar enclosure for our experiment, as this enclosure allows a good view of the foraging ravens, the wild boars themselves do not represent a risk for the ravens, and the ravens are known for responding well to playbacks of heterospecific and conspecific calls at this location (Nácarová et al, 2018). A total of 48 trials were conducted in three different seasons, starting in spring 2019 (17 January 2019-7 May 2019), followed by autumn (25 September 2019-18 December 2019) and finishing in summer 2020 (25 May 2020-18 July 2020), with two non-testing periods of approximately 4 and 7 months between seasons.…”

Differential Survival In Carrion Crows Through Eavesdropping on Human Speech: An Agent-Based Model

“…Frid and Dill (2002) suggested that "disturbance stimuli should be analogous to predation risk" and list vigilance as a response to disturbance. These disturbance stimuli include vocalizations of other species, as eavesdropping on heterospecific vocalizations allows individuals to detect the presence of a predator (Magrath et al, 2015).Common ravens (Corvus corax), for instance, respond to playback of jackdaw (Corvus monedula), blue jay (Cyanocitta cristata), European jay (Garrulus glandarius), and laughing gull (Leucophaeus atricilla) alarm calls with flight or vigilance (Davídková et al, 2020;Nácarová et al, 2018).…”