Thieving northwestern crows steal food more "politely" from their immediate kin than from birds that are less closely related to them, according to scientists in the US, writes Natasha Gilbert.
The birds, for which pinching food from other crows is a way of life, adapt their stealing tactics depending on how closely related the victim is, according to Renee Ha of the psychology department at the University of Washington.
Using DNA analysis, the researchers determined which of 55 foraging crows were related and then observed the population over two years.
The study, published in the journal Bird Behaviour , describes how the crows silently sidled up to kin and pilfered food items without much of a fuss raised in response.
With more distantly related crows or non-kin, scroungers dive-bombed victims, screeching as they went, and, in return, the victims tried to defend their food.
According to the study, dominant status does not play a role in this behaviour. "Relatedness between individuals determines whether the interaction is passive or aggressive," it states.
Kin selection is well known for directing altruistic behaviour among related individuals of some species, but this is the first time it has been observed in foraging strategies.
The researchers suggest that this discriminatory behaviour may have arisen because thieves could benefit by acting aggressively towards non-kin, who are not important to their loves. But to do so towards kin would not make evolutionary sense.
However, explaining how the crows know which bird is a relation and which is not remains elusive.
Dr Ha said: "These crows have highly developed cognitive skills and can tell who their relatives are."
Gilbert Roberts of the Evolution and Behaviour Research Group based at the University of Newcastle told The THES : "How they do it is a mystery."