1. Department of Comparative Cognition, Institute of Biology, University of Neuchâtel, Neuchâtel, Switzerland.
2. Department of Comparative Language Science, University of Zurich, Zurich, Switzerland.
3. Center for the Interdisciplinary Study of Language Evolution (ISLE), University of Zurich, Zurich, Switzerland.
4. School of Psychology and Neuroscience, University of St Andrews, St. Andrews, Scotland.