.... I ...... want to know if a swamp harrier hawk would be able to pick up our chickens..... Please tell me if you think the hawk will threaten our hens!!....
I am not a Kiwi so take that into consideration, but I don't know of a hawk species that is able to pickup and flyaway with a grown standard size hen or rooster.
Observe how difficult it is for the hawk in this video to move a RLR hen even 6 inches. If i am correct I think that 6 inches is equal to about 150mm in New Zealand terms. Whether the hawk can leave with your hens or not is immaterial because your chicken will in any case be dead.