The most common and most likely answer to this crossword clue is the 4 letter word TERN
I've seen this crossword clue in The Times
T
E
R
N
More clues leading to the result TERN
- Part of winter nasty for bird
- Seabird — or wader with bit missing?
- In winter, noticing seabird
- Aquatic bird shot for speaker
- Wings of the raven? Another bird
- Aquatic bird’s back, not head
- Sherry’s medium in tradename large schooner
- Reportedly go off bird
- Bird act for the audience
- One of two birds you might spot in winter nest
Buddy explains!

The straight part
We know that "bird" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case bird = tern.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 TERN mean?
TERN noun- Any of various sea birds of the family Sternidae that are similar to gulls but are smaller and have a forked tail.
- That which consists of, or pertains to, three things or numbers together.
- A lottery prize resulting from the favourable combination of three numbers in the draw.
- Threefold; triple; consisting of three; ternate