Mutual Wattle Ornaments in the South Island Saddleback (Philesturnus carunculatus) Function as Armaments

Many birds have ornamental traits that are expressed in both sexes. Wattles—colorful fleshy structures that hang from the lower bill—are frequent among birds, but remain poorly understood and are generally presumed to be under sexual selection. The South Island saddleback (Philesturnus carunculatus) is an endangered bird endemic to New Zealand in which both males and females possess wattles. We used behavioral observations, morphological measures, and a playback experiment to investigate the role of wattles in saddlebacks during territorial encounters. Wattles were monomorphic when controlled for body mass, and became engorged with blood in both sexes during visual displays. In a playback experiment using male song, wattle engorgement was significantly associated with territorial intrusions in males but not in females. However, female wattle engorgement was significantly more likely during playback experiments in the absence of their mate, suggesting wattles are used in territorial defense by both sexes. The markedly similar use of wattles by both males and females in visual displays as a response to territorial intrusions supports the hypothesis that these elaborate structures function in part as armaments.