FOR BIRD BRAINS ONLY
Credit: Parade Magazine
September 13, 2015
Marilyn vos Savant

These bird names follow a rule:

PARROT
PIGEON
ROBIN
SPARROW

These bird names do not follow the rule:

CARDINAL
ORIOLE
THRUSH
WREN

What is the rule?

Answer:

The name has to be composed of two shorter words in a row (rob + in).