Published online 10 February 2009 in Wiley InterScience (. interscience.wiley). DOI 10.1002/ajp.20668 Received 2 October 2008; revised 8 January 2009; revision accepted 9 January 2009 Contract grant sponsor: Lucie Burgers Foundation for Com- parative Behaviour Research. Ã Correspondence to: Sonja...