It nests in colonies close to the sea in rock crevices and lays a single white egg.

However, Birds Korea (2010) state that c. 100,000 pairs nest on Gugeul Islet, implying that possibly over 75% of the global population breed on one very small island.

In structure it most resembles a Leach's storm petrel with its forked tail, longish wings, and flight behaviour, but does not have a white rump and the call differs.

It is difficult to distinguish from other all-dark Hydrobates species, and the first English record had to be DNA-tested to eliminate the possibility that it was a Leach's storm petrel, since populations of north-eastern Pacific Leach's storm petrels contain individuals that show completely dark rumps.

Only in storms might this species be pushed into headlands, but even then an out of range bird would probably defy definite identification.

[6] The population is expected to undergo a moderately rapid decline over the next three generations, owing primarily to the impact of introduced species.