Spooner's at large -- trek to find amphibian! (4,4)

I believe the answer is:

tree frog

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'amphibian' is the definition.
(tree frog is a kind of amphibian)

I can't explain the remainder of the clue.

(Other definitions for tree frog that I've seen before include "High jumper" , "Amphibian found in the branches?" , "Arboreal amphibian" .)

I've seen this clue in The Telegraph.

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