swamp harrier travels

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When I visited Lord Howe Island in May 95, I saw a Swamp Harrier crusing 
over the lagoon. According to a publication I borrowed at the time 
(sorry, don't recall the ref) they are regular visitors to the island 
from ... ? Maybe Jervis Bay as Lorne mentioned.

But migration over the sea to another site is different to the question 
of peregrines (etc) hunting over the sea.

As to what advantage this confers -- I guess one thought is that prey 
over water may have less opportunity to skulk away from an attack. But 
how does the falcon pick up the prey? I'm not a PF expert, but I thought 
they retreived the prey from the ground, post-strike. They certainly 
would not do that over the sea. can they/do they retrieve form mid-air?

Stephen Mugford