Eavesdropping involves the extraction of information from signalling interactions by individuals not

directly involved. Such behaviour has been conclusively demonstrated by experiments that present

songbirds with simulated singing interactions in which the roles of interactants were varied by changing

the timing of songs. We examined the phenomenon of song type matching by presenting male great

tits, Parus major, with simulated interactions in which one interactant switched song type such that it

matched (or not) that sung by the opponent. Subjects responded to simulated intrusion by previously

heard interactants by singing significantly shorter songs in response to males that switched (i.e. used two

song types), regardless of whether or not matching occurred, compared with those that used one.

Subjects also showed a significantly lower level of approach behaviour to males whose opponents had

switched song types but not matched. Male great tits are therefore capable of extracting different kinds

of information by eavesdropping on interactions between others and using that information when

deciding how to respond to subsequent intrusion. These results confirm and expand our knowledge on

the potential of eavesdropping to provide accurate information on the likely strengths and weaknesses

of potential rivals