The adult black-collared hawk has a more or less white head, tinged with buff, and with black shaft streaks on the crown.

The female lays three to five eggs, dull white, spotted with pale yellow-brown or red-brown and a few darker freckles.

[4][5] In the 1870s, Ridgeway wrote that Busarellus (then known as Ichthyoborus) had the "general form and appearance of Buteogallus aequinoctialis", but that it "is much more nearly related to the heliatine groups", in which he included Milvus, Haliastur, and Haliaaetus.

This feature is shared with Ictinia and with the group of true milvine kites and sea eagles (Milvus, Haliastur, Haliaaetus, and Icthyophaga).

Within the buteonine group, Ictinia is near-basal, and Busarellus is a member of a clade shared with Geranospiza, Rostrhamus, and Helicolestes.