Nose dive (or perhaps beak dive)

There are always a flock of black-headed gulls on the castle moat in winter.  They don't get their dark brown heads until the breeding season (their heads aren't blackas the name implies).  

On my walk this morning I was watching them dive into the moat and come up with tiny fish and other food often to have it stolen by others in the flock.  There's no sense of fair play in the natural world!