When perched, several species of small falcons, including American Kestrels (Falco sparverius), often pump their tails, but the possible function of this behaviour is unknown. Our objective was to use observations and experiments to examine the possible function(s) of tail-pumping by American Kestrels. Fieldwork was conducted from March 2015 to December 2015 at the Blue Grass Army Depot in Madison County, Kentucky. During observations of focal kestrels, we noted their behaviour (e.g. landing on a perch, hunting, or consuming prey), including when and how often they pumped their tails (i.e. rapid movement of the tail down, then back up to its original position). Kestrels typically tail-pumped when landing on a perch (mean = 4.1±0.2 pumps per 10 s) and consuming prey (mean = 2.4±0.2 pumps per 10 s). When hunting, kestrels tail-pumped at higher rates during the 30 s prior to attacking (mean = 1.1±0.3 pumps) than they did during the 30–60 s interval before an attack (mean = 0.3±0.1 pumps). During experiments where kestrels were presented with models of a conspecific and a predator (Cooper's Hawk, Accipiter cooperi), we found no difference in rates of tail-pumping prior to and during the presentation. These results suggest that tail-pumping by American Kestrels is not used either to communicate with conspecifics or as a predator-deterrent signal. Rather, kestrels appear to tail-pump to help maintain balance on perches when landing and consuming prey. In addition, prior to attacking prey, kestrels typically bob their heads (possibly to aid in judging distances), and tail-pumping may help them maintain stability as they head-bob and prepare to attack.

中文翻译：

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美国红隼（Falco sparverius）尾抽的可能功能

栖息时，包括美洲红隼 (Falco sparverius) 在内的几种小型猎鹰经常翘起尾巴，但这种行为的可能功能尚不清楚。我们的目标是使用观察和实验来检查美洲红隼的尾巴抽动的可能功能。实地考察于 2015 年 3 月至 2015 年 12 月在肯塔基州麦迪逊县的蓝草陆军仓库进行。在观察焦点红隼期间，我们注意到它们的行为（例如落在栖木上、狩猎或吃掉猎物），包括它们何时以及多久抽动尾巴（即尾巴快速向下移动，然后回到原来的位置） . 红隼在降落在鲈鱼上（平均 = 4.1±0.2 泵每 10 秒）和消耗猎物（平均 = 每 10 秒 2.4±0.2 泵）时通常会尾部抽水。打猎时，红隼在攻击前的 30 秒内以更高的速率（平均值 = 1.1±0.3 泵）比在攻击前的 30-60 秒间隔期间（平均值 = 0.3±0.1 泵）进行尾部泵送。在将红隼与同种和捕食者（Cooper's Hawk，Accipiter cooperi）模型一起展示的实验中，我们发现展示之前和期间的尾巴抽动率没有差异。这些结果表明，美洲红隼的尾巴抽动既不用于与同种交流，也不用作捕食者威慑信号。相反，红隼似乎会尾抽，以帮助在着陆和吃掉猎物时保持栖息处的平衡。此外，在攻击猎物之前，红隼通常会摇头（可能是为了帮助判断距离），尾巴抽动可以帮助它们在摇头和准备攻击时保持稳定。