Male and female golden whistlers respond differently to static and dynamic signals of male intruders

Bird displays vary widely in their sensitivity to changes in signaler condition. Plumage ornaments are generally static and undergo minimal change. Behavioral ornaments, by contrast, are dynamic and may track signaler condition or motivation more closely. The relative importance of each trait type in signaling individual quality has been examined during female choice, but rarely in territorial defense. Male golden whistlers (Pachycephala pectoralis) display both a static plumage signal (throat patch) and a dynamic signal (song) during territorial disputes. We examined sex differences in the responses of territorial pairs to these traits during simulated territory intrusions by decoy males that had either normal or experimentally reduced throat patch sizes, in combination with low or high singing rates. Males paid attention to both categories of signals when estimating rival threat, responding for longer toward males with normal throat patches, and spending more time close to the intruder in high song rate trials. In contrast, females responded differentially only to dynamic signals. Patch size may reflect a male's long-term viability and status, whereas singing rates may correlate with willingness to escalate contests. As females participate in joint territorial defense and interactions between neighbors are sex specific, the song rates of intruding males may provide clues to their partners' motivation to escalate contests. By contrast, knowledge of an intruding male's intrasexual competitive abilities (signaled via patch size) may be unimportant to females. Differences in the signaling properties of static and dynamic signals may maintain the existence of multiple antagonistic signals in this species.