Double-crested cormorants breed as far west as the Islands of Four Mountains. The colonies vary in size from a few to 25 pairs. Pelagic and red-faced cormorants nest from Amak to Attu on nearly every island. Relative abundance of the two in mixed colonies varies between areas as well as from year to year. Red-faced cormorants tend to nest in colonies mixed with kittiwakes and murres, but pure colonies also occur. Pelagic cormorants occupy isolated, small colonies, but they also nest with kittiwakes and murres and are often found with red-faced cormorants. By far the densest concentration of cormorants occurs in the Near Islands, especially at Attu, where an estimated 77,000 birds were seen in 1970. In the Aleutians as a whole, red-faced cormorants outnumber pelagic cormorants, and double-crested cormorants make up only a very small percentage of the breeding population.
Parasitic Jaeger (Stercorarius parasiticus)
The distribution of jaegers is poorly known because investigators have spent little time ashore on most islands. Murie (1959) found jaegers on a number of islands, and most of the data in Fig. 5 are his. Population estimates are available only for Amchitka (25 pairs; White et al. 1977) and Buldir (30-40 pairs; G. V. Byrd, unpublished data).
Glaucous-winged Gull (Larus glaucescens)
Glaucous-winged gulls no longer nest on islands where foxes occur except where islands in lakes are available. Most colonies are on offshore rocks or islets and range in size from a few pairs to over 200 pairs, and occasionally more. They are found throughout the Aleutians, but the largest known colonies are at Bogoslof (500 pairs) and Buldir (250 pairs).
Black-legged Kittiwake and Red-legged Kittiwake (Rissa tridactyla and R. brevirostris)
Black-legged kittiwakes breed locally in every major island group, usually mixed with murres and cormorants. The large colonies contain over 25,000 birds, but colonies of less than 50 pairs also occur. Red-legged kittiwakes breed only on Buldir and Bogoslof. They are remnants of a previously more widespread population.
Arctic Tern and Aleutian Tern (Sterna paradisaea and S. aleutica)
Terns breed locally in each island group. Both species occur at Attu, Amchitka, Adak, and Umnak, but only arctic terns are found at Nizki. Factors limiting distribution are unknown. Colonies vary in size from less than 10 pairs to 100 pairs.