What unusual feature do these 5 words have in common?

AFTERNOON
ALLEGRETTO
HIBISCUS
HOLDOVER
INTRAVENOUS

HINT:
The answer involves hidden words.

Answer:

Each clue word conceals the name of a bird:

afTERNoon
allEGRETto
hIBIScus
holDOVEr
intRAVENous 

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