They impress - by their circus performances? (5)
I believe the answer is:
seals
'performances?' is the definition.
The definition and answer can be both related to communication as well as being plural nouns.
Maybe there's an association between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for seals that I've seen before include "Fastens or closes securely" , "Makes waterproof" , "They make an impression" , "they're impressive" , "Marine mammals" .)