It is predominantly known from the bone fragments of six specimens found in guano deposits and caves on Ascension Island and described by Philip Ashmole, Kenneth Edwin Laurence Ryder Simmons, and William Richmond Postle Bourne in 2003.

They are great and high like herons, the belly white and the back black as coal, the bill like to a cormorant; when they are killed they cry like hogs.

The name "aponard" is attested by Jacques Cartier, who used it for the great auk in a report on a Northwest Atlantic expedition a few years earlier.

Cartier's reports aroused considerable interest among the educated French around 1550, and it is quite likely that Thévet himself had read them and that they were his source for the name.

Whether Thévet invented his "aponar" in yet another attempt to make his book more interesting - as he was wont to - or whether his testimony is in fact a description of the Nycticorax is hard to decide.