Hemiprocnidae: The Treeswifts
Ethan like these fellows more than normal swifts because they actually land sometimes. He has recorded all 4 of the Treeswifts.
Hemiprocne mystacea (Mustached Treeswift)
Hemiprocne comata (Whiskered Treeswift)
Hemiprocne coronata (Crested Treeswift)
Hemiprocne longipennis (Gray-Rumped Treeswift)
The excellent species name refers to the tailfeathers.