Seabird or two, as we can hear (4)

I believe the answer is:

erne

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'seabird' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

(Other definitions for erne that I've seen before include "Island-studded lake in Fermanagh" , "Fish-eating sea eagle" , "Light (a flame)" , "'Sea-eagle, river and lough (4)'" , "Irish lough" .)

I've seen this clue in The Everyman puzzle in The Observer.

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