Possible Clues:

• It may be heard in an aviary
• *Repeated tweets
• Way to claim territory, perhaps, for a lark
• Dawn chorus of it
• Boy on road overwhelmed by huge sound from the skies?
• With call of nature, boy on time - good!
• Heard when some flappers are vocal
• Harmonious twittering
• Good to follow women on Twitter
• Call from a cage