Flight dynamic and typical of gadfly petrels, using dynamic soaring with occasional flaps and high arcs above the wave surface to move rapidly over large distances. In winds greater than 10 knots, adopts a sinusoidal motion, one wing pointed at the water, the other at the sky. This species typically does not follow ships, although individuals may investigate (often as a fast flyby!) "chum"-slicks for potential food. Black-cappeds occasionally form small intraspecific rafts during the day, flushing away from the approaching boat. These petrels feed in such rafts, or individually, picking food items such as squid from the ocean surface. This species comes to land only at dusk and under the cover of darkness, to breed in remote, high elevation locations.
Non-breeders apparently migrate north and east from the Caribbean into the waters of the Carolina bight, where the species is easily seen on pelagic trips during temperate spring and summer periods. During the 1980s and 90s it became clear that this species is locally abundant in the Gulf Stream waters off the US mid-Atlantic states, frequenting waters 400 m or deeper (Brinkley and Patteson 1998). Recorded on most pelagic trips out of Oregon Inlet or Hatteras, North Carolina. Largest numbers occur during mid summer and early fall and comprise birds in a variety of plumage states. In late fall (mid October), the adults begin to return to breeding areas. A few (e.g., non-breeders) remain in the Gulf Stream during January to April.
Social and interspecific behavior
Females apparently return to the Gulf Stream during December to feed and fatten before the eggs are laid. Occasionally forms rafts of tens of individuals and presumably concentrations in the tens of birds, as seen in the Gulf stream and in Cuban waters, are regular occurrences.
Small mammals probably are frequent predators of eggs.