When young, frigate birds will play with a stick, chasing each other for it and if they drop it, another catches it. Like lion cubs at play they are practising how they will hunt. Frigatebirds catch fish in flight, specialising on flying fish and following schools of tuna so as to catch the smaller fish that leap out of the water to escape them.
Frigate birds are pirates, they will hassle other seabirds in flight, forcing them to regurgitate their food and then swoop down and catch it (like the stick they used to play with as children). They also steal the entire nests of other birds and some female frigate birds feed on the chicks of other birds.
Thank you Ian Northcott