Possible Clues:

• Kind of swallow
• Remain south (anag) — migratory bird
• Black-and-white bird
• Bird seen round buildings could be tame in hours
• Bird initially heard by river leading right into the sea
• Same changes in time and money to swallow
• One having a flutter can ruin family if suffering reverse
• Relative of swallow
• Eaves-mud-nest builder