Status signals have evolved for individuals to avoid energetic and physical costs of resource defense. These signals reflect an individual’s competitive ability and therefore influence competitors’ decisions on how to invest in a fight. We hypothesized that the response of receivers to status signals will depend on the social context. During territorial defense, group members may provide support to a territory owner by participating in defense. We investigated whether the presence of juveniles—who group together with territorial males—alters the territorial male’s attack decisions and level of aggression in the black-crested titmouse (Baeolophus atricristatus). Crest-length in this species functions as status signal. We simultaneously presented two taxidermic male models in a territory: one with an unmanipulated crest and one with a modified shortened crest. Models were presented to males that had resident juveniles cohabiting on their territory, and to males without juveniles. During intrusions, juveniles actively defended against the simulated intruders by approaching and sometimes attacking. The presence of juveniles affected how territorial males responded to the status signals of the intruders: when juveniles were present, males were more likely to first attack the model with the unmanipulated crest (i.e., longer, and more threatening), compared to males residing without juveniles. This suggests that juvenile support alters the risk-taking decision of the territorial male. To our knowledge, this is the first indication that behavioral responses to a status signal depends on the presence of supportive group members. Status signals can indicate relative quality of animals and can therefore be used to evaluate a competitor when deciding whether or not to fight over resources. The black-crested titmouse has been shown to use its crest length as a status signal during fights over food. In our study, we assessed if this status signal is also used in territorial defense, by conducting an experiment where we presented two taxidermic male models with different crest sizes to a territorial male. We also investigated whether juvenile presence influenced which model was attacked. In trials where juveniles were present, territorial males attacked the longer crested model significantly more often than in trials where territorial males were alone. This suggests that the presence of juveniles, which help the male defend the territory, allows the male to attack the more aggressive-appearing intruder.

中文翻译：

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社会分组对黑冠山雀（Baeolophus atricristatus）领土防御行为的影响

个人的状态信号已经进化，以避免资源防御的精力和体力成本。这些信号反映了个人的竞争能力，因此会影响竞争者如何投资战斗的决定。我们假设接收者对状态信号的反应将取决于社会背景。在领土防御期间，团体成员可以通过参与防御来支持领土所有者。我们调查了与领地雄性聚集在一起的幼鸟的存在是否会改变领地雄性在黑冠山雀（Baeolophus atricristatus）中的攻击决定和侵略程度。该物种的波峰长度作为状态信号。我们同时在一个地区展示了两个动物标本剥制男性模型：一种带有未经处理的波峰，另一种带有经过修改的缩短波峰。模型被展示给在其领土上同居的幼鱼的雄性，以及没有幼鱼的雄性。在入侵期间，青少年通过接近和有时攻击来积极防御模拟入侵者。幼鱼的存在影响了领地雄性对入侵者的地位信号的反应：当幼鱼在场时，雄性更有可能首先攻击带有未经处理的冠的模型（即更长，更具威胁性），而没有居住在其他地方的雄性则少年。这表明幼年的支持改变了领地雄性的冒险决定。据我们所知，这是对状态信号的行为反应取决于支持小组成员的存在的第一个迹象。状态信号可以表明动物的相对质量，因此可用于在决定是否争夺资源时评估竞争对手。黑冠山雀已被证明在争夺食物时使用它的冠长作为状态信号。在我们的研究中，我们通过进行一项实验来评估这种状态信号是否也用于领土防御，在该实验中，我们向领土男性展示了两个具有不同波峰大小的动物标本剥制术男性模型。我们还调查了青少年的存在是否会影响被攻击的模型。在幼鱼在场的试验中，领地雄性比领地雄性单独的试验更频繁地攻击长冠模型。这表明帮助雄性保卫领地的幼鱼的存在，