Honest signalling, dominance hierarchies and body condition in House Sparrows Passer domesticus (Aves: Passeriformes) during acute coccidiosis

Parasitic infections may change the equilibrium between the costs and benefits of an animal for maintaining its status in a social group. Consequently, parasites may influence the social status of an animal in a group. The present study investigated whether acute infection with Isospora spp. has any effect on the social relationships (e.g. dominance hierarchy) of male house sparrows and how the infection influences their behaviour, immune status, and body condition. Furthermore, the study allowed us to examine how important the 'badge of dominance' is with respect to maintaining social status even when the actual condition is changing as a result of infection. The results obtained showed that an acute infection leads to changes in the dominance hierarchy of a social group and that body mass losses of birds depend on the achieved hierarchy status. A positive correlation between the badge size and male aggressiveness was only found during acute infection. In addition, we also found a relationship between cell-mediated immune response and male aggressiveness during acute infection. This suggests that male badge size is not sufficient to maintain a given dominance position. On the other hand, badge size, a signal developed during the moult, appears to remain an informative and 'honest' signal several months later, reflecting the energy reserves of a bird faced with a demanding stressful situation such as acute infection. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99, 718-726.