36 



P. C. SEKORA, G. V. BYRD, AND D. D. GIBSON 



since swirling "clouds" of birds are en- 

 countered. 



Even when the estimates of birds seen are 

 assumed to be accurate, data interpretation is 

 complex. Lack of information on diurnal 

 rhythms adds difficulty to data interpreta- 

 tion. Counts of burrow-nesting birds (e.g., 

 puffins) have been inaccurately interpreted 

 because of the lack of understanding of their 

 nesting ecology. Gulls (Larus spp.), terns, and 

 jaegers (Stercorarius spp.) are not well known 

 since shore parties have seldom investigated 

 island interiors. Nocturnal species (e.g., an- 

 cient murrelet, Synthliboramphus antiquus, 

 and storm-petrels, Oceanodroma spp.) are per- 

 haps the least known. Since only crude esti- 

 mates of colony sizes are available, broad 

 limits are used in this paper to describe known 

 colonies. 



Status and Distribution 

 of Breeding Seabirds 



Even from the sparse literature available, it 

 is apparent that some seabird populations are 

 now drastically different from those in the 

 Aleutians around 1900. Changes in nesting 

 habitat due to volcanic eruptions, tidal waves, 

 marine erosion, and earthquakes have oc- 

 curred for centuries, and colonial nesting bird 

 populations have fluctuated accordingly. In 

 addition, native Aleuts used marine birds and 

 their eggs for food and their skins for cloth- 

 ing, but the Aleuts were so diminished in 

 numbers by 1900 that they have had little re- 

 cent effect on the bird populations. 



From about 1900 to 1936, arctic foxes were 

 introduced to most of the Aleutians for fur 

 farming. The foxes lived on birds in summer, 

 and some species (e.g., Aleutian Canada 

 geese, Branta canadensis leucopareia) were 

 wiped out wherever foxes were introduced. 

 Ground-nesting and some burrow-nesting sea- 

 birds were also drastically reduced or extir- 

 pated on many islands. 



During World War II the thousands of 

 troops in the Aleutians brought dogs and cats 

 to some of the islands as pets, and many of 

 the animals were set free when the men de- 

 parted. The military also accidentally intro- 

 duced Norway rats to some of the islands. 

 Their role in seabird population reductions is 



unknown. 



Figures 2-15 (pages 40-46) present data on 

 the distribution of populations of birds that 

 have survived the foxes and other introduced 

 predators. An annotated list of seabirds 

 breeding in the Aleutians follows. 



Annotated List of Species 

 Northern fulmar (Fulmarus glacialis) 



Northern fulmars breed on only three is- 

 lands: Buldir (200 pairs), Gareloi (1,500 pairs), 

 and Chagulak (more than 100,000 pairs). 

 Fulmars were apparently much more wide- 

 spread formerly (Murie 1959; Turner 1886). 

 Introduced foxes were probably involved in 

 the decline. 



Fork-tailed Storm-petrel and Leach's 

 Storm-petrel (Oceanodroma furcata and 

 O. leucorhoa) 



The distribution of storm-petrels is poorly 

 known due to their nocturnal behavior near 

 the nesting colonies. The presence of birds has 

 generally been noted by finding them aboard 

 ships anchored near islands after darkness. 

 Population estimates are not available for any 

 colonies, so symbols used in Fig. 3 indicate 

 probable numbers of breeding birds. In few 

 cases have active burrows or crevices been 

 discovered. Storm-petrels were formerly 

 much more common. Murie (1959) and John L. 

 Trapp (personal communication) found large 

 numbers of storm-petrel remains in fox dens. 

 Most present breeding colonies are probably 

 confined to offshore islets and fox-free 

 islands. 



Double-crested Cormorant, Pelagic 

 Cormorant, and Red-faced Cormorant 

 (Phalacrocorax auritus, P. pelagicus, 

 and P. urile) 



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 oc- 

 cupy isolated, small colonies, but they also 



