Related Clues:

• See 20-Across
• Chirrup
• Bird's sound
• Chirp rapidly
• A series of chirps
• Trill
• Chirp
• Tweet
• Bird sanctuary excitement
• Palpitate
• Twitter
• Site with the tagline 'What are you doing?'
• Trendy social network
• Microblogging service
• Forum for 140-character messages