The stains on the body and wings are vital in the defense of the territory. Males with larger spots are more effective at chasing away their non-territorial rivals and are more successful in contests within aviaries. A staining of the black as part of an experiment, 64% of males lost their territories, while only 8% of control subjects did. However, males whose wings had been dyed before they had mated could still attract females and successfully reproduce. In the sergeant thrush, the spots on the wings are a sign of threat among males and have an unimportant role, if any, in intersex encounters. Therefore, the spots are likely to have evolved in response to pressures linked to intrasexual selection.