224 



R. D. JONES AND G. V. BYRD 



(mostly Sitka spruce, Picea sitkensis) on 

 every military base in the "Chain." 



Rats appear to be the most commonly intro- 

 duced predators on a worldwide scale. Ships 

 furnish the traditional source of their intro- 

 duction, but one of us (R.D.J.) has observed 

 them disembarking from a military aircraft at 

 Cold Bay on the Alaska Peninsula. These ani- 

 mals probably entered the plane at Adak, 

 which received rats from military ships early 

 in World War II. 



Rats may be able to exploit a larger percent- 

 age of the seabird species on a given island 

 than other introduced predators because they 

 can enter crevices and burrows in search of 

 the birds and their eggs and young. They also 

 destroy ground-nesters, and cliff-nesters may 

 not be altogether safe from them. Clayton M. 

 White (personal communication) found that 

 Rattus norvegicus had ravaged every one of 

 16 eyries of the peregrine falcon (Falco pere- 

 grinus) that he checked in 1971 at Amchitka 

 Island, Alaska. Only one egg had tooth 

 marks, however. Kenyon (1961) ascribed the 

 disappearance of the song sparrow (Melospiza 

 melodia maxima) and the winter wren (Troglo- 

 dytes troglodytes kiskensis) from Amchitka 

 to predation by rats. 



Many authors have mentioned potential rat 

 damage, but few have quantitatively docu- 

 mented it. Imber (1974), however, provided 

 data concerning the magnitude of rat preda- 

 tion on diving petrels and storm-petrels on 

 some New Zealand islands. He found that rats 

 were taking between 10 and 35% of the chicks 

 of gray- faced petrels (Pterodroma macroptera 

 gouldi) on Whale Island in the parts of the 

 colonies where burrows were dense. On those 

 parts of the island with a very low density of 

 petrel burrows, rats were believed to have 

 killed virtually every chick. Imber revealed 

 that where Polynesian rats (Rattus exulans) 

 occur, diving petrels and storm-petrels are 

 rare or absent, though they are widespread on 

 neighboring islands. Imber concluded from 

 his studies of the ecology of petrels and Poly- 

 nesian and Norway rats that a petrel colony is 

 endangered if invaded by a species of rat 

 whose maximum weight approaches or ex- 

 ceeds the mean adult weight of the petrel. 

 Harris (1970), who worked with dark-rumped 

 petrels (Pterodroma phacopygia) on Santa 

 Cruz in the Galapagos Islands, indicated that 



black rats (Rattus rattus) were responsible for 

 the extremely low nesting success of the 

 petrels there. 



In British Columbia, Campbell (1968) re- 

 corded predation by the Alexandrian rat 

 (R. rattus) on ancient murrelets (Synthli- 

 boramphus antiquus) at Langara Island. The 

 extent of damage to the murrelet population 

 is not known. 



The animals most widely introduced in 

 Alaska seabird habitat are the red fox ( Vulpes 

 fulva) and the arctic fox. The red fox is native 

 to the Alaska Peninsula and to the eastern- 

 most group of islands in the Aleutians, known 

 as the Lissii or Fox Islands (Berkh 1823; 

 Murie 1959). At the other end of the archipel- 

 ago, in the group known as the Near Islands, 

 Attu Island has a native population of the 

 arctic fox (Tikhmenev 1861; Bancroft 1886). 

 Between Umnak Island, the westernmost is- 

 land of the Fox group, and Attu there are no 

 native terrestrial mammals, and substantial 

 avian populations evolved an ecology in the 

 absence of mammalian predation (Murie 

 1959). 



At the time of Russian contact with the 

 Aleutians, both fox species were dominantly 

 dark phase, and the early introductions 

 (about 1836) by the Russian- American Com- 

 pany were of both species (Tikhmenev 1861). 

 Initially both species were successful in de- 

 veloping insular populations, but in the long 

 run the arctic fox proved the more successful. 

 At Great Sitkin, Adak, and Kanaga, intro- 

 duced red foxes maintained populations that 

 were eliminated in the 1920's to be replaced 

 by arctic foxes (unpublished records of the 

 Aleutian Islands National Wildlife Refuge). 

 Differential harvest of the preferred dark 

 phase had in the meantime altered the genetic 

 makeup of the population, and the light phase 

 had become dominant. In the arctic fox popu- 

 lations, the dark phase remained generally 

 dominant at about 95%, but in some small is- 

 lands with limited genetic stock (e.g., the 

 Semichis) the proportion approached one to 

 one (unpublished records of the Aleutian Is- 

 lands National Wildlife Refuge). 



By 1936, the Aleutian archipelago consti- 

 tuted a large-scale fox farm, which in its 23 

 years of existence as a refuge had produced 

 25,641 fox pelts with a value of $1,162,826. 

 During the same period, and perhaps earlier, 



