What unusual feature do these five words have in common?

KNOWLEDGE
MICROWAVE
OVERHEARD
PROBING
TREMULOUS

HINT:
The answer involves hidden words.

Answer:

Each clue word conceals the name of a bird:

knOWLedge
miCROWave
oveRHEArd
pROBINg
trEMUlous

Credit: GAMES/World of Puzzles
June, 2017
Stephen Sniderman
WINGING IT  II