Sympatric divergence of risk sensitivity and diet menus in three species of tit

Divergent diet menus could cause sympatric divergence of risk sensitivity; however, evidence is not yet available for the functional link between diet menu and risk sensitivity. We investigated risk sensitivity (measured as the discount intensity for probabilistic rewards) and diet menu (insectivory and granivory) among three sympatric species of tits (family Paridae): varied tits, Poecile varius, marsh tits, Poecile palustris, and great tits, Parus major, which form mixed-species foraging flocks in Japan. Binary choice tests, offering rewards of differing amount and probability, were conducted in the laboratory. Great tits and marsh tits were found to be risk prone (and more insectivorous), whereas varied tits were risk averse (and more granivorous). Diet menus were examined in the laboratory using behavioural titration tests between sunflower seeds and mealworms. The results of these tests were similar to patterns of food exploitation determined using stable isotope analysis (delta C-13 and delta N-15 contents) of blood samples from birds collected in the wild. Possibly, the dominant varied tits drove the other two species of tits towards different diet menus and unusually high risk proneness. In future, we should examine whether different interspecies interactions cause different risk sensitivity in other geographical environments. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.