The white-collared kite is 49–50 cm in length and 550–580 g in weight. The adult has a grey head with white hindneck, black upperparts, white underparts, and a grey tail with a very broad, black subterminal band and whitish tip. It is very similar to the more southerly distributed gray-headed kite (Leptodon cayanensis) and was often merged into it as a subspecies.
This species is classified as Critically Endangered. There have been very few sightings of it, and nothing is known of its feeding or breeding ecology. The areas in which it has been sighted, in coastal Alagoas, Pernambuco and Paraíba, have been subject to massive deforestation. The current population is estimated at some 50–249 mature individuals.
The binomial commemorates the British zoologist William Alexander Forbes.