Some species of birds use their vocalisations to communicate predator presence and the level of threat they pose, including two species of corvids (Corvidae), American Crows (Corvus brachyrhynchos) and Siberian Jays (Perisoreus infaustus). Our objective was to determine if Blue Jays (Cyanocitta cristata), another corvid, also use specific calls or vary the characteristics of certain calls to convey information about the level of threat posed by aerial predators. During the non-breeding seasons of 2014 and 2015, we recorded and analysed the vocal responses of Blue Jays to study skins of six species of raptors that varied in size and the level of threat they pose to Blue Jays. Experiments were conducted at seven locations in Madison County, Kentucky. The mean number of Blue Jays present during trials was 2.6, and Blue Jays uttered five different vocalisations during trials, with ditonal and monotonal jeers given most frequently. The rate at which Blue Jays uttered ditonal jeers differed among trials, with rates highest during trials with an Eastern Screech-Owl (Megascops asio) and a Sharp-shinned Hawk (Accipiter striatus). However, the characteristics of ditonal and monotonal jeers (duration, low frequency, high frequency, and peak frequency) did not differ among trials. These results suggest that Blue Jays may either perceive Eastern Screech-Owls and Sharp-shinned Hawks as the greatest threats or, alternatively, as potential, but less threatening predators, and, therefore, they were willing to take greater risks when mobbing them. In contrast, Blue Jays mobbed the other raptors, i.e. American Kestrels (Falco sparverius), Red-tailed Hawks (Buteo jamaicensis), and Great Horned Owls (Bubo virginianus), with much less intensity, likely because they posed less of a threat or, in the case of Cooper's Hawks (Accipiter cooperii) that are known predators of Blue Jays, perhaps because mobbing with greater intensity, e.g. approaching more closely, posed too great a risk. Blue Jays in our study used the same calls with the same characteristics when responding to potential predators, only calling rates differed. However, such variation in calling rates when mobbing would likely provide useful information about the presence of, and possibly the threat posed by, potential predators for conspecifics and, perhaps, heterospecifics.

中文翻译：

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蓝鸟（Cyanocitta cristata）对掠食性威胁不同的猛禽的反应

一些鸟类使用它们的声音来传达捕食者的存在和它们构成的威胁程度，包括两种鸦科（Corvidae）、美洲乌鸦（Corvus brachyrhynchos）和西伯利亚松鸦（Perisoreus infaustus）。我们的目标是确定另一只鸦科蓝鸟 (Cyanocitta cristata) 是否也使用特定的叫声或改变某些叫声的特征来传达有关空中掠食者威胁程度的信息。在 2014 年和 2015 年的非繁殖季节，我们记录并分析了蓝鸟的声音反应，以研究六种猛禽的皮肤，这些猛禽的大小和它们对蓝鸟构成的威胁程度各不相同。实验在肯塔基州麦迪逊县的七个地点进行。试验期间出现的蓝鸟平均数量为 2.6，和 Blue Jays 在审判期间发出了五种不同的声音，最常发出的是双调和单调的嘲讽。Blue Jays 发出双音调嘲讽的比率在不同的试验中有所不同，在与 East Screech-Owl (Megascops asio) 和 Sharp-shinned Hawk (Accipiter striatus) 的试验中比率最高。然而，双调和单调嘲笑的特征（持续时间、低频、高频和峰值频率）在试验之间没有差异。这些结果表明，蓝鸟可能将东方尖叫猫头鹰和锋利的鹰派视为最大的威胁，或者将其视为潜在但威胁较小的掠食者，因此，他们在围攻它们时愿意承担更大的风险。相比之下，蓝鸟队围攻了其他猛禽，即美洲红隼（Falco sparverius），红尾鹰 (Buteo jamaicensis) 和大角鸮 (Bubo virginianus) 的强度要低得多，可能是因为它们构成的威胁较小，或者就 Cooper's Hawks (Accipiter cooperii) 而言，它们是蓝鸟的已知捕食者，也许是因为更密集的围攻，例如更接近，会带来太大的风险。我们研究中的蓝鸟在回应潜在的掠食者时使用具有相同特征的相同呼叫，只是呼叫率不同。然而，围攻时呼叫率的这种变化可能会提供有关同种和异种的潜在捕食者的存在以及可能构成的威胁的有用信息。s 老鹰 (Accipiter cooperii) 是蓝鸟的已知捕食者，这可能是因为更密集的围攻，例如更接近，会带来太大的风险。我们研究中的蓝鸟在回应潜在的掠食者时使用具有相同特征的相同呼叫，只是呼叫率不同。然而，围攻时呼叫率的这种变化可能会提供有关同种和异种的潜在捕食者的存在以及可能构成的威胁的有用信息。s 老鹰 (Accipiter cooperii) 是蓝鸟的已知捕食者，这可能是因为更密集的围攻，例如更接近，会带来太大的风险。我们研究中的蓝鸟在回应潜在的掠食者时使用具有相同特征的相同呼叫，只是呼叫率不同。然而，围攻时呼叫率的这种变化可能会提供有关同种和异种的潜在捕食者的存在以及可能构成的威胁的有用信息。