Heard dullards are pigs (5)

I believe the answer is:

boars

I'm a little stuck... Click here to teach me more about this clue!

'are pigs' is the definition.
(I have seen 'Male pigs' mean 'boars' so perhaps 'pigs' could also mean 'boars')

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for boars that I've seen before include "Male or wild pigs" , "Wild swine" , "Male badgers" .)

I've seen this clue in The Mirror.

Want a hint initially instead of a full solution? Install my app