Tracks of birds (5)

I believe the answer is:

rails

I believe this clue is a double definition.

'tracks' is the first definition.
(I know this)

'birds' is the second definition.
(rail is a kind of bird)

'of' is the link.

(Other definitions for rails that I've seen before include "Water birds" , "Metal bars of a barrier" , "Makes a protest" , "secretive birds" , "Barriers of horizontal bars and supports" .)

I've seen this clue in The Telegraph and The Globe and Mail.

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