Common Black Hawk
Buteogallus anthracinus
The adult common black-hawk is 43–53 cm (17–21 in) long and weighs 930 g (33 oz) on average. It has very broad wings, and is mainly black or dark gray. The short tail is black with a single broad white band and a white tip. The bill is black and the legs and cere are yellow. The adults resemble zone-tailed hawks, but have fewer white bars on their tail and are larger in size. Sexes are similar, but immature birds are dark brown above with spotting and streaks. Their underparts are buff to whitish with dark blotches, and the tail has a number of black and white bars.
ID text from Wikipedia, CC BY-SA 4.0

Great Black Hawk
Buteogallus urubitinga
The adult great black hawk is 56 to 64 centimetres (22 to 25 in) long and weighs 1.1 kilograms (2 lb 7 oz). It resembles the common black hawk, but is larger with a different call and tail pattern. It has very broad wings, and is mainly black. The short tail is white with a broad black tip. The bill is black and the legs and cere are yellow. The sexes are similar, but immature birds are dark brown above with spotting and streaks. Their underparts are buff with dark spots, and the tail has a number of black and dusky bars. The call of the great black hawk is a distinctive piping ooo-wheeeeee.
ID text from Wikipedia, CC BY-SA 4.0

Where you might meet both
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Play today's Daily BirdPhotos and recordings are credited to their authors under the licence shown. Full profiles: Common Black Hawk and Great Black Hawk.