Nepotistic alarm calling in the Siberian jay, Perisoreus infaustus

Abstract

From a life history perspective, parents have an incentive to protect their reproductive investment, and so may provide care even after their offspring are independent. Such prolonged parental care could lead to postponed dispersal of the offspring and thereby facilitate the formation of kin groups. We tested whether alpha birds in Siberian jays protected their independent, retained offspring by giving alarm calls during simulated predator attacks. We compared the responses to predator attacks simulated by flying a hawk model over a dyad of birds on a feeder for dyads composed of an alpha bird and either a relative or a nonrelative. Alpha females were nepotistic in their alarm-calling behaviour, in that they called more frequently when accompanied by their retained offspring than by unrelated immigrants, but alpha males called indiscriminately. This difference in alarm calling could reflect dominance relationships in Siberian jay groups, because the presence of immigrants may be less costly to alpha males, but alpha females are more vulnerable to competition from immigrants. Alarm calls were usually given during escape, when both individuals in the dyad had left the feeding site. However, results of a playback experiment suggest that alarm calls conveyed information about danger and incited an immediate escape reaction. Our results indicate that alarm calling can be nepotistic, and that factors other than kinship influence alarm-calling behaviour. Nepotistic antipredator behaviours are benefits that offspring can gain only in their natal territory. Hence, in the absence of preferential treatment by their parents, offspring may be more likely to disperse and kin groups are prevented from forming.