The White-collared Kite is a large sized kite, with mostly slate upperparts and a white lower body. White hind collar, white underwing coverts and reduced barring in under surface of secondaries are diagnostic features. It has a longish tail with variable band pattern that should not be used by itself for identification.
The White-collared Kite can be distinguished from its sister species, the Gray-headed Kite Leptodon cayanensis, by the white color of the hind collar, instead of an inconspicuous and undelimited medium to pale neutral gray; mostly white in the underwing coverts rather than all black; and under surface of the secondaries predominantly white with greatly reduced black barring. The number of white and black tail bands in the White-collared Kite is variable, and not a good diagnostic character (Dénes et al. 2011)
The following paragraphs from Seipke et al. (2011) discuss other similar looking ("black-and-white") raptor species occuring in North-east Brazil:
Short-tailed Hawk Buteo brachyurus juveniles can show very pale cheeks and eyebrows making head look almost white under certain light conditions or angles. In flight, wings are pointed and lack noticeable fingers. Barring on tail is not as obvious. On perched birds, look for bright yellow cere (not orange or grey). Toes are long in the hawk, but short on the kite. Primaries reach tail tip on perched Short-tailed Hawk.
Mantled Hawks Pseudastur polionotus soar with wings held above the horizontal (dihedral) or on flat, broad, rounded wings with white trailing edges and all-white tail (dark banding at base hard to notice). Beware of white leading edge, a feature shared with White-collared Kites. On perched birds, look for broadly white-tipped secondaries, and dark primaries reaching or surpassing tail tip.
White-necked Hawks Buteogallus lacernulatus soar on a dihedral and show a black band on the trailing edge of wings. As in White-collared Kites, the tail has a subterminal black band. On perched birds primaries reach or fall short of tail tip. Both Mantled and White-necked Hawks usually soar with tail fanned, unlike White-collared Kites.
Black-and-white Hawk-Eagle Spizaetus melanoleucus has a flight silhouette virtually identical to that of juvenile Short-tailed Hawk, but head and leading edge of wings are white as in White- collared Kites, and Mantled and White-necked Hawks.
Crane Hawks Geranospiza caerulescens, while very different in coloration from White-collared Kites, can look remarkably similar in flight silhouette (smallish head, longish tail, bowed, rounded wings with noticeable ‘fingers’); especially on glides and with a cloudy background. Look for white crescents on primaries.