This paper presents the ”Mixed Societies of Robots and Vertebrates” project that is carried out by the Mobile Robotics group at EPFL, Switzerland in collaboration with the Unit of Social Ecology at the Free University of Brussels, Belgium. The idea of the project is to study behavior in young chicks of the domestic chicken (Gallus gallus domesticus) by using mobile robots able to interact with animals and accepted as members of an animal group. In contrast to other studies where relatively simple robotic devices are used to test specific biological hypotheses, we aim to design a multipurpose robot that will allow ethologists to study more sophisticated phenomena by providing a wide range of sensors and sufficient computational power. In this paper we present a PoulBot robot and give an example of the ethological experiment, where it is used to study the social aggregation in chick groups.