Dangling? I need some help

Question

"Some seagulls squawked briefly when she stepped by them and quickly flapped away."

I wonder that the bold part modifies for "some seagulls" or "when she stepped by them"?

p/s: I added a comma to make sure the bold part modifies for "some seagulls".Is it correct?

"Some seagulls squawked briefly when she stepped by them, and quickly flapped away."

Answer 1

And quickly flapped away isn't a modifier, so it doesn't modify anything. It's one of two coordinated predicates:

Some seagulls
    [squawked briefly when she stepped by them] 
    [and quickly flapped away]
.

Both bracketed phrases predicate on the subject some seagulls. Neither is a modifier.