The Wedge-rumped Storm-Petrel, formerly known as the Galapagos Storm-Petrel is a small species and appears to be most closely related to the Least Storm-Petrel (Halocyptena microsoma). Once confirmed it may then require the Wedge-rumped to be shifted to the Halocyptena genus. The present English name highlights the triangular shape of the white rump patch, in itself distinctive. Quite unusual is that the Wedge-rumped Storm-Petrel is the only storm-petrel that visits its colonies during the day, at least in the Galapagos population. On the well known Genovesa Island colony, Short-eared Owls (Asio flammeus galapagoensis) is a major predator of the storm-petrels. It is hypothesized that they conduct diurnal visits to the colony because they are largely nocturnal foragers. However, there is a separate subspecies (kelsalli) that breeds on islands off Peru and Chile in the Humboldt Current and these birds are typically nocturnal at the colonies as is the norm in the family. During the non-breeding season the species ranges north to at least central Mexico, and south to northern Chile.