The most common and most likely answer to this crossword clue is the 8 letter word BLACKCAP
I've seen this crossword clue in Independent
B
L
A
C
K
C
A
P
More clues leading to the result BLACKCAP
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 = blackcap.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 BLACKCAP mean?
BLACKCAP noun- A small Old World warbler, Eurasian blackcap (Sylvia atricapilla), which is mainly grey with a black crown.
- Any of various species of titmouse (of the family Paridae), including the black-capped chickadee (Poecile atricapillus, syn. Parus atricapillus).
- An apple roasted until black, to be served in a dish of boiled custard.
- Whitebark raspberry (Rubus leucodermis).