The most common and most likely answer to this crossword clue is the 7 letter word MIGRATE
I've seen this crossword clue in The Guardian
M
I
G
R
A
T
E
More clues leading to the result MIGRATE
- Move abroad, developing ragtime
- One Greek taken in by friend, having to move abroad
- What one Greek moving into China does?
- Aircraft speed’s to move from one system to another
- Relocate speed of fighter?
- My! Tremendous sound as birds gather to do this
- Good speed following motorway journey
- I’m coming over to grind up sticks
- Plane on rail, get the drift?
- Noodling ragtime might make you move back and forth
Buddy explains!

The straight part
We know that "birds gather to do this" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case birds gather to do this = migrate.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 MIGRATE mean?
MIGRATE verb- To relocate periodically from one region to another, usually according to the seasons.
- To change one's geographic pattern of habitation.
- To change habitations across a border; to move from one country or political region to another.
- To move slowly towards, usually in groups.
- : To move computer code or files from one computer or network to another.
- To induce customers to shift purchases from one set of a company's related products to another.