The most common and most likely answer to this crossword clue is the 5 letter word HERON
I've seen this crossword clue in Financial Times
H
E
R
O
N
More clues leading to the result HERON
Buddy explains!

The straight part
We know that "Wading bird" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case wading bird = heron.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does HERON mean?
HERON noun- A long-legged, long-necked wading bird of the family Ardeidae.