尾下覆羽 meaning in Chinese

lower tall coverts
under tail coverts

Dark - centred undertail coverts = dark - sided flycatcher ( white in grey - streaked )
暗色为中心的尾下覆羽=鲜卑? (乌? ) (灰斑?的是白色的)
As you cannot see the rumps of any of these birds and the undertail coverts lack salmon tones i would be reluctant to call them lesser cuckoos
由于在图片中无法看到这几只鸟的腰部而且尾下覆羽不带橘红色味，个人对称?们为小杜鹃有所保留。