What is "hydropsalis"

Hydropsalis is a genus of nightjar in the Caprimulgidae family. It contains the following species:

• Ladder-tailed nightjar (Hydropsalis climacocerca)
• Scissor-tailed nightjar (Hydropsalis torquata)
• Spot-tailed nightjar, (Hydropsalis maculicaudus)
• White-tailed nightjar, (Hydropsalis cayennensis}