燕卷尾身长从7英寸25英寸(18~64cm)不等。燕卷尾通常为黑色，带有淡绿色、淡紫色或淡蓝色的光泽。燕卷尾是技术超群的飞翔能手，在抓捕昆虫的过程中，它既能俯冲又能翻转飞行。
我们认为卷尾燕已经进化到警示斑点鹃自己的存在。通过帮助斑点鹃种群更有效率地捕食来寻找更多偷取食物的机会。
We think that drongos have evolved to alert babblers to their presence because helping the group forage more effectively leads to more frequent opportunities for theft.
通常，卷尾燕栖息在斑点鹃种群的巢穴上部，一次又一次地俯冲下来偷取食物。
Traditionally, the drongo perches above a crowd of foraging pied babblers and swoops in from time to time to steal its catch.
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