Marsh bird’s method of travel (4)

I believe the answer is:

rail

This clue is a double definition.

'marsh bird's' is the first definition.
(I've seen this in another clue)

'method of travel' is the second definition.

(Other definitions for rail that I've seen before include "wader" , "A bird; bar to hang on" , "Track - complain - bird" , "Bar - marsh bird" , "Bar; waterside bird" .)

I've seen this clue in The Times.

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