Last updated March 13, 2018 at 4:15 pm
Dinner invitations are far from a simple process for the common raven.
Researchers have discovered that the distinctive “haa” calls used to alert others to food foraging sites provide clues about the age and sex of the caller, which in turn helps those in earshot decide whether or not to accept.
The invitation may in large part be a request to provide safety in numbers at a site made potentially dangerous by the presence of predators or territorial breeding pairs.
Between summer of 2009 and winter 2010, researchers from the University of Vienna and the University of Cambridge studied a population of free-ranging common ravens (Corvus corax) that regularly gathered during the feedings of wild boar at the Cumberland Wildpark Grünau in Austria.
Each feeding session was video- and audio-recorded to identify vocalising individuals, with 418 calls of 12 individuals analysed.
Ravens can tell other birds apart
The team found that the vocal signals emitted to alert conspecifics to feeding sites varied in frequency, call duration and amplitude, according to their age and sex.
This suggests that ravens have the necessary variation in their food calls and the cognitive means to distinguish between specific classes of sex and age (class-recognition), according to Dr Markus Böckle, a Research Associate in the Department of Psychology at Cambridge.
“Thus, we show for the first time that ravens can potentially use food calls to tell other ravens apart, according to these categories,” he said. “This gives ravens the opportunity to use information about the caller in decision-making processes, such as whether to join or avoid foraging groups.”
In simple terms, class-recognition of unknown callers could allow ravens to assess the degree of competition for food and decide whether to join a specific feeding situation or not.
“It is important to note that ravens use these calls to primarily refer to food items but at the same time transmit more information than just the presence of food,” Dr. Böckle said.
“Calls referring to external objects like food are frequently thought of as precursors of language. Our results add further insights into raven intelligence and their complex feeding behaviour.”
Most previous research on call characteristics in ravens has focused on recognition of known individuals. The researchers believe their experiments were the first to test for features in food calls that might provide information about unknown individuals.
The paper published in Frontiers in Zoology.