Melanin-based coloration predicts aggressiveness and boldness in captive eastern Hermann’s tortoises

Although body coloration is often used in social interactions, few studies have tested whether it is linked to a suite of behavioural traits. We examined whether among captive adult male eastern Hermann’s tortoises, Eurotestudo boettgeri, behavioural patterns covary with eumelanic coloration of the shell. Dark eumelanic males were more aggressive in male–male confrontations and bolder towards humans. These relationships were independent of body size and ambient temperature. Activity level and exploration were not significantly associated with coloration. We conclude that, at least in captivity, melanic shell coloration predicts agonistic behaviour towards conspecifics and fearfulness towards humans (i.e. boldness).