The most common and most likely answer to this crossword clue is the 4 plus 3 plus 4 letter word SKIN AND HAIR
I've seen this crossword clue in The Guardian
S
K
I
N
A
N
D
H
A
I
R
Buddy explains!
The straight part
We know that "They often fly together in a row" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they often fly together in a row = skin and hair.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.