Segítő zebrapintyek: Kooperáció vagy kényszer?

Abstract

The evolution of cooperation between non-kin animals has been explained by mutualism. Altruistic assistance is costly, but if reciprocated the costs diminish. However, recent studies suggest that reciprocity between non-kin animals is a rare phenomenon (Clutton-Brock, 2009). In the present study we assessed whether zebra finches (Taeniopigya guttata) were able to cooperate in an instrumental task. An earlier study revealed that keas can solve similar problems, but on the other hand rooks failed in a test, which was originally worked out for chimpanzees. Both parrots and rooks are considered exceptionally intelligent. The subjects of our research are small songbirds and to our best knowledge cooperation in songbirds have not been studied in instrumental tests. We worked out a method for small songbirds to assess cooperation in obtaining food. Basically, we present the birds’ tidbits in a plastic cup attached to the top of the cage. The birds do not have direct access to the cup and can eat the tidbits only when lifted by a seesaw by the partner. In any such action one of the birds must be altruistic to let its partner gain the reward. Breeding pairs and 4 female-female pair were successful in using the seesaw. However, assistance was asymmetric in each pair, one of the birds became helper and the other one did not return the assistance. We tested assistance in five different combinations of the 8 females, in order to understand the reason of asymmetry. Our results show that each of the birds understands the task - all of them played the helpers role - therefore asymmetric assistance can not be a consequence of asymmetric cognitive abilities. Our preliminary results suggest that rank order in the pairs may be the cause of non-mutual help. It seems dominant individuals may use mild coercive tactics against subordinates. This observation is congruent with recent theory on the evolution of assistance giving between non-kin animals.