The concept of territoriality does not apply very well to pelagic "colonial" nesting seabirds. Tropicbirds disperse from their nesting sites to feed and fly out of sight of land to forage over a patchy and sometimes motile marine resource. They do not defend foraging areas and when seen at sea they are seldom in groups of more than two or three. Most frequently they are seen as lone individuals. Nesting tropicbirds make use of available cavities under rocks, on ledges in cliffs or caves and sometimes under vegetation. They do not share nesting cavities, but often suitable nesting sites are in close proximity. Literature describing nesting colonies is actually an artifact of suitable multiple nesting sites occurring in a defined area. Geological suitability determines nest selection more than a bird's preference for close proximity. Successful pairs reuse the same nest cavities year after year and these are vigorously defended. We found densities of pairs on Saba to be up to sixty pairs per hectare. Isolated nest sites where nest cavities are limited are not uncommon.
This species is monogamous. A change in breeding pairs is presumed to be a result of mortality. On Saba birds congregate four to six weeks prior to nesting to examine cavities and await the return of their mate. While flying around the sight one bird emits an extended high-pitched kreeee call to initiate courtship flight. As many as eight to ten birds join the calling bird. Eventually the mated pair distances themselves from the group and begins a highly synchronized aerobatic and noisy courtship flight. One of the pair moves above the other with wings extended downward until almost touching the upward extended wings of the bird below. Streamers are swished. Sometimes the streamers of the upper bird are lowered to touch the streamers of the bird below. They climb, then suddenly swoop down to the water surface before spiraling upward again. This is repeated many times before the pair flies to their nest where all copulation occurs.