Hunters
Hooked bills and strong talons are often indicators of an actively predatory bird. Raptors immediately come to mind---hawks, eagles, owls, falcons, vultures. These birds (not all closely related) consume a staggering variety of prey, from insects to fish to other birds to monkeys and young ungulates. Even some songbirds set their sights on bigger quarry than bugs: Shrikes, for example, are passerines that will skewer rodents and lizards on thorns and barbed wire for relaxed consumption.
Fishers
The versatility of wings gives birds enviable prowess in capturing fish, whether it's penguins "flying" after schools underwater or kingfishers dive-bombing quiet forest streams. Some wading birds, such as herons and egrets, are adept at stalking and spearing fish and can even be seen prowling backyard and garden ponds.
Bug-eaters
Many smaller birds subsist at least partly on insects. Some specialists include the nighthawks, commonly seen looping in twilight skies over open meadows and fields during North American summer. Woodpeckers have evolved their idiosyncratic---and noisy---foraging style to skewer grubs, ants and the like within tree bark.
Seed-splitters and Nutcrackers
Many birds, especially passerines, consume seeds and nuts on a seasonal basis. The diversity of bill shape, the heft and length reflect different approaches. Northern cardinals, for example, have short and heavy beaks, optimal for breaking big, hard-shelled seeds, while the lighter bill of the American tree sparrow is better suited for smaller fare (References 1). Clark's nutcrackers, inhabiting the mountains of the American West, are famous for caching pine nuts across a broad swath of country and then---remarkably---re-locating their stockpiles.
And More...
The dietary variation goes on and on: Flamingos strain invertebrates and algae from shallow waters; hummingbirds target succulent nectar; grouse down huckleberries, and ducks nibble aquatic plants.
