Siberian jays are sneaky little rascals.
These tiny corvids can use bird lies to try and trick other flocks into leaving a territory, so that the interlopers can move in and nick their food.
But it seems that other Siberian jays (Perisoreus infaustus) are also wise to this ruse. New research has found that breeding members of a family group can distinguish between the warning cries of their own flock, and the warning cries of would-be trespassers.
Amongst the smaller and fluffier of the corvid family, Siberian jays are quite fascinating birds. They mate for life and tend to live in small flocks of fewer than 10 members, with one dominant breeding pair. Within this group, they have been found to exhibit nepotistic alarm calling: when danger is nearby in the form of a predator, they sound a cry that will alert family members, telling them to scarper.
But the use of these cries is not always on the up-and-up. Like a number of other animals, including primates, Siberian jays use their warning calls to straight-up lie to other flocks of Siberian jays.
It can be a rewarding strategy: Siberian jays are highly territorial and difficult to oust, but the cost of ignoring a predator warning is potentially very high indeed. If it works, the new flock can muscle in on the territory and stores of food therein that the jays put away for the lean winter months, without having to resort to physical altercation.
To observe this in action, and also to see how the birds avoid being fooled, ornithologist Filipe Cunha of the University of Zurich in Switzerland and evolutionary biologist Michael Griesser of the University of Konstanz in Germany designed an experiment for wild jays in their natural habitat, specifically the breeding members of the local flock.
They set up a feeder with a speaker nearby, and placed a lump of pig fat to lure in foraging birds, along with a video camera set-up to record the birds' actions. Through the speaker, the scientists played warning calls from other Siberian jays - those that were former members of the bird's own flock, those from flocks in neighboring territories, and those from birds the target bird had never encountered before.
"Our results demonstrate that Siberian jays respond differently to playbacks of warning calls depending on the social relationship to the caller," the researchers wrote in their paper.
"Breeders immediately escape to safety when exposed to warning calls from former group members but not when exposed to warning calls from neighbors or unknown breeders. Siberian jays are familiar with all their neighbors and encounter them on a daily basis, but neighbors are more likely to give deceptive warning calls than individuals from their own group.
"Moreover, neighbors compete for space and the associated resources. Thus, familiarity alone does not breed trust, but Siberian jays trust only warning calls of former cooperation partners."
This naturally raises the question of why false calls are given at all, but we already have an answer. A previous experiment by Griesser showed that the breeders of a flock, when feeding together with juveniles, will immediately leave a feeder when a warning cry is given no matter who gives it, perhaps in order to teach the youngsters about the danger signals as well as ensure their safety.
Since lying can sometimes yield satisfactory results, the jays have a solid motivation for continuing to deceive their neighbors.
What is not clear, is at which point and how the young jays learn to recognize the calls of their own flock, and distinguish them from those of neighbors and strangers. Future research could help reveal more about this process, as well as determine the differences in the calls themselves.
"Trusting only signals of cooperation partners may facilitate the evolution and maintenance of communication systems vulnerable to deceptive signaling," the researchers wrote.
"Similarly to Siberian jays, humans also are more likely to trust individuals that belong to the same group and therefore are more likely to be cooperation partners. Thus, vulnerability for deception may also be a driver of rapid diversification of languages and facilitate the formation of dialects, being signifiers for local groups of cooperators."
The research has been published in Science Advances.