Answer:

wren

Answer	Crossword Clue
WREN	Brown bird
WREN	St. Paul's Cathedral designer
WREN	Architect and bird

WREN	Marsh bird
WREN	Small songbird
WREN	Songbird
WREN	St. Paul's Cathedral architect
WREN	Architect Christopher
WREN	Great English architect
WREN	Small brown singer
WREN	Designer of St. Paul's

WREN	St. Paul's architect
WREN	Dark brown songbird
WREN	"Troglodytes" member
WREN	Avian songster
WREN	Small warbler
WREN	Small passerine bird
WREN	Birdhouse nester
WREN	"Beau Geste" author

WREN	Small tweeter
WREN	Birdhouse songbird
WREN	Drury Lane Theatre architect
WREN	Charles II's royal architect
WREN	English astronomer-turned-architect
WREN	1674 architect of Theatre Royal, Drury Lane
WREN	Avian warbler
WREN	Birdhouse bird

WREN	Cactus ..: state bird of Arizona
WREN	Singer of complex songs
WREN	Small, vocal bird
WREN	Little songbird
WREN	Twittering bird
WREN	Architect Sir Christopher
WREN	Architect with an avian name
WREN	Small singing bird

WREN	Little Jenny of nursery rhyme fame
WREN	Brown songbird
WREN	Brownish songbird
WREN	Cactus ... (state bird of Arizona)
WREN	Designer of St. Paul's Cathedral in London