The most common and most likely answer to this crossword clue is the 9 letter word CORNCRAKE
I've seen this crossword clue in The Daily Telegraph
C
O
R
N
C
R
A
K
E
More clues leading to the result CORNCRAKE
Buddy explains!

The straight part
We know that "grassland bird" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case grassland bird = corncrake.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 CORNCRAKE mean?
CORNCRAKE noun- A bird of the rail family, Crex crex, that breeds in meadows and arable farmland across Europe and western Asia, migrating to Africa in winter.