There is another factor to consider, however. The limited number of specimens now available from the Gulf of Alaska indicates that separate subspecies occupy the eastern and western Gulf of Alaska. The accepted boundary is somewhere in the vicinity of Prince William Sound. This is an indication that there has been a hiatus in this area of rather long duration. I have speculated that this sort of break may be in some way related to the length of day and a period during the summer when there is little darkness to cover activities near the colony. Thoresen (1964) and Cody (1973) have both reported that western gulls (Larus occidentalis) assemble in Cassin's auklet colonies on moonlit nights to prey on arriving adults. It is likely that other nocturnal species would provoke the same sort of hunting tactic. A light-related predation factor implies that the predators rely on sight. Avian predators are indicated.
Leach's Storm-petrel (Oceanodroma leucorhoa)
Even less well understood than the breeding distribution of the fork-tailed storm-petrel is that of Leach's storm-petrel.
Bendire (1895) quotes notes from Chase Littlejohn, who found Leach's storm-petrel to be an abundant breeder on unspecified small islands near Sanak in 1894. It greatly outnumbered the fork-tailed storm-petrel. On his visit in 1937 Murie (1959) learned that all of the large colonies of seabirds that had once existed there were gone. He attributed this to overfishing and associated perturbation and to the introduction of fox. No systematic assessment of seabirds on Sanak has been attempted since Littlejohn's time.
No Leach's storm-petrel colonies have been encountered during reconnaissance surveys of the Gulf of Alaska. Small numbers have been reported from time to time and while it is very much less abundant than the fork-tailed storm-petrel, I expect that it will be found in small numbers at various places in the Gulf of Alaska when it becomes possible to make more thorough searches. It may occur in remote areas like the smaller islands scattered throughout the Sandman Reefs—possibly even in large numbers. On the basis of the Sanak record, we must assume that this storm-petrel has been greatly reduced in numbers, at least in the western portion of the Gulf.
Double-crested Cormorant (Phalacrocorax auritus)
The white-crested cormorant, the race of the double-crested cormorant residing in the Gulf of Alaska, is principally an inhabitant of the marine environment. This cormorant is a common, but apparently patchily distributed, resident throughout the northern and western Gulf of Alaska.
Gabrielson and Lincoln (1959) thought that it nested only from Kodiak Island westward into the Aleutians. However, it probably breeds from Yakutat Bay westward. Isleib and Kessel (1973) estimated the abundance of the double-crested cormorant along the North Gulf Coast as several thousands, about one-tenth as common as the pelagic cormorant. It is the third most abundant of the four cormorant species nesting in the area. It occurs as scattered inclusions in many colonies throughout the area, and at least in the Shumagin Islands, even occurs in some colonies by itself.
There are no data on which to base an estimate of any change in status. It probably is not much affected by many of the naturally occurring perturbations.