Population ecology of seabirds on Middleton Island, Alaska. Population ecology of seabirds on Middleton Island, Alaska. The situation on Middleton is a particularly severe example of poor breeding performance in kittiwakes, but many other colonies in Alaska have exhibited low productivity since at least the mid 1970s.
Circumstantial evidence points to an inadequate food supply as the cause of poor productivity.
In contrast to kittiwakes, glaucous-winged gulls have increased exponentially on Middleton, from fewer than 1,000 birds in the late 1970s to more than 15,000 by the early 1990s. Gulls are the principal predators on the eggs and young of other species, including kittiwakes. It is difficult to argue conclusively that food supply is the ultimate determinant of kittiwake productivity when a population is faced with intense predation pressure such as currently occurs on Middleton. Other species also show definite trends on Middleton. Information on adult survival is needed to assess the particular life stages affected by untoward changes in the environment and, most importantly, the time of year and locations at which those changes occur.