Interrelations Between Seabirds and Introduced Animals

Robert D. Jones, Jr.

U.S. Fish and Wildlife Service
1011 East Tudor Road
Anchorage, Alaska 99507

and

G. Vernon Byrd [66]

U.S. Fish and Wildlife Service
Aleutian Islands National Wildlife Refuge
Adak, Alaska

Abstract

Animals introduced to insular seabird habitats are of both intentional and accidental origin. The results of the introductions—particularly of herbivores—cannot be predicted, but may range from severely destructive to beneficial. Herbivores are of both domestic and wild stocks of ungulates, hares, and rabbits. Rats are the most commonly introduced omnivore on a worldwide basis. In Alaska the commonest carnivore introduction has been the red fox (Vulpes fulva) and arctic fox (Alopex lagopus), and the first of these were made in the early 19th century by the Russian-American Company. These foxes nearly extirpated the Aleutian Canada goose (Branta canadensis leucopareia) from its nesting grounds. Black flies (Simuliidae), which are vectors of avian blood parasites, have been introduced to three of the Aleutian Islands.

The purpose of this paper is to discuss some influences of introduced animals, primarily mammals, on seabirds and their nesting habitat, with emphasis on the coasts of Washington, British Columbia, and Alaska. Our discussion focuses on island introductions partly because a large proportion of seabirds choose island nesting sites, and because islands present ecosystems vulnerable to such introductions.

Flightless animals have no means of immigration, hence little probability of colonizing islands. In these circumstances marine birds evolve populations in relatively simple ecosystems (Carlquist 1965; MacArthur and Wilson 1967), though the degree of simplicity depends on several variables, including the island's size and its distance from a source of immigrants. These systems have achieved ecological homeostasis through reciprocal adaptation over an extended period. Experience has shown that introductions to such systems result in severe perturbations (Odum 1971:221).

The introductions can be categorized as being either intentional or accidental events. Effects of such introductions have varied widely, depending on the type of animal introduced, the types of birds present and the habitat they occupy, the size and shape of the island, the type of nesting area used by the birds, and the status of their populations before the introduction. An example drawn from our Aleutian experience with gallinaceous birds illustrates the interaction of these variables. The dark phase of the arctic fox (Alopex lagopus) was introduced to Adak and Amchitka islands, both of which had native populations of the rock ptarmigan, Lagopus mutus (Gabrielson and Lincoln 1959). Foxes were released on Adak in 1924, and on Amchitka in 1921. Adak has an area of 751 km² and Amchitka 350 km². Adak is irregular in shape with extensive precipitous shorelines, relatively few beaches, and a large, central mountainous hinterland which foxes rarely penetrated. Amchitka, on the other hand, presents a zone of marine planation on its eastern two thirds, low mountains on the rest, shelving beaches around most of the island, and a long, linear, narrow shape that foxes explored completely. By 1949 ptarmigan were difficult to find on Amchitka, and then only in the highest, steepest section of the mountains. They were extirpated from the low, eastern two thirds of the island. The foxes flourished on Amchitka, but did much less well on Adak, where the ptarmigan population fluctuated in a normal cyclic manner, apparently uninfluenced by the foxes. Then the foxes were eradicated on Amchitka in the 1950's, and by 1962 the ptarmigan had spread over the whole of the island and become one of the most conspicuous avian features of the landscape.

Animal Introductions

Non-predatory Animals

Man has taken ungulates with him to many islands. Although numerous records of livestock introductions are available, few provide information relating to the effects of these animals on the habitat and their fauna unless the impact has been severe.

A most noteworthy example of destruction by ungulates occurred on Guadalupe Island off the coast of Baja California. Domestic goats (Capra hircus) were introduced in the unrecorded past with the result that little of the once abundant vegetation remains. In its place introduced species capable of withstanding heavy grazing are abundant over most of the island. Several endemic avian species are now considered extinct, including the Guadalupe storm-petrel, Oceanodroma macrodactyla (Howell and Cade 1954; Jehl 1972).

Sheep (Ovis aries) have been introduced to seabird nesting islands with varying results. In Bass Strait, Australia, Norman (1970) studied the effects of introduced sheep on vegetation and birds. He cited various papers attributing destruction of colonies of shearwaters (Puffinus sp.) to the activities of sheep, primarily their treading on the burrows. He found, however, that on Big Green Island and Phillip Island, sheep were not responsible for declines in shearwater breeding success, nor did they prevent expansion of colonies.

Other authors have reported damage to seabird nesting areas by sheep. One such example in the eastern North Pacific region concerns Protection Island, Washington. According to Richardson (1961), 100 to 300 sheep grazed freely on the island since 1958. He reported damage by grazing and frequent trampling of nesting areas of rhinoceros auklets (Cerorhinca monocerata). Landslides were initiated by these activities, rendering the slopes unusable by auklets. Of the burrows in his study area, 46% were buried by slides. He did not determine mortality.

Other avian consequences may flow from sheep introductions. Husbandry of these ungulates has been practiced with varying success for many years in the Aleutian Islands, most notably on Umnak and Unalaska islands, both of which have large native populations of bald eagles, Haliaeetus leucocephalus (Gabrielson and Lincoln 1959). Before the introduction of sheep, these raptors were oriented to the sea, hunting fish and seabirds. Sheep presented a new resource and presently the industry found itself confronted by a formidable predator, and demanded that eagles be destroyed (letter to William Egan, Governor of Alaska, from James S. Bynum, Secretary-treasurer, Umnak Company, Inc.).

Other ungulates introduced on Alaska islands include cattle (Bos taurus) on Chernofski and Chernabura islands; caribou (Rangifer tarandus) on Adak; reindeer on St. Matthew, Nunivak, Atka, Umnak, St. Paul, St. Lawrence, Hagemeister, and Kodiak as well as many interior locations; deer (Odocoileus hemionus) on Kodiak and Afognak; elk (Cervus canadensis) on Afognak; and musk oxen (Ovibos moschatus) on Nunivak. All these animals have maintained populations on islands for a time, and some appear likely to do so into the distant future. Specific effects on seabirds is generally not known, but trampling of grassy slopes such as that reported for sheep develops in some cases. Bailey et al. (1933) speculated that nests of the snow goose (Anser caerulescens) were destroyed by reindeer or their herdsmen in the Point Barrow area.

The destruction of vegetation by introduced rabbits and hares has been documented for many areas in the world. This destruction has often extended to seabirds. Perhaps the most dramatic example occurred on Laysan Island in the Hawaiian archipelago, where rabbits of unknown species were introduced in 1903. According to Warner (1963) it took less than 20 years for the rabbits to remove every green plant but three patches of Sesuvium portulacastrum. The Laysan duck (Anas laysanensis) was brought perilously close to extinction. The rabbits were eliminated in the 1920's, and the population of ducks increased to over 600 by 1963, a figure thought to approximate the pre-disturbance population.

European hares (Lepus europaeus) were introduced on Smith, San Juan, and Long islands, in Washington. On Smith Island, these burrowing animals apparently grazed nearly all the succulent vegetation close to the ground. By 1924, their burrows riddled the bluffs, causing them to cave into the ocean (Couch 1929). Couch found no seabirds nesting on the island, but found numerous tufted puffins (Lunda cirrhata) present on the bluffs, but not nesting. A removal campaign was directed against the hares in 1924 and in a few years they were gone. Smith Island now supports nesting pelagic birds (D. Manuwal, personal communication).

Accounts of hare and rabbit introductions to islands are legion, but not all such introductions have drastically affected seabirds. Manana Island, Hawaii, is such a case. Tomich et al. (1968) believed that introduced rabbits (Oryctolagus cuniculas) were not even indirectly detrimental to the nesting noddies (Anous tolidus) and sooty terns (Sterna fuscata). In some situations, introduced lagomorphs have been credited with benefiting seabirds. Lockley (1942) suggested that rabbits helped to open new breeding colonies of manx shearwaters (Puffinus puffinus) at Skomer and in west Wales in general. In Alaska rabbits were introduced to Middleton Island in 1952 (Rausch 1958) and to Ananiuliak Island at an earlier unrecorded date. Both have developed sustaining populations in the presence of large seabird populations without measurable effect on the birds. On Ananiuliak glaucous-winged gulls (Larus glaucescens) have been observed feeding on rabbits (W. S. Laughlin, personal communication).

Invertebrates have been introduced on three islands in the Aleutians. The black fly (Simulium sp.) reached Adak by 1958, Shemya by 1964, and Amchitka in connection with activities of the Atomic Energy Commission in 1968. Apparently the insects were transported on jet aircraft. The pest appears well established on Adak, but its status on the other two islands is uncertain. Like the mosquito, the female black fly sucks blood from warm-blooded animals, and in the process becomes the vector of a Leucocytozoan blood parasite of birds. In years of black fly abundance at Seney (Michigan) National Wildlife Refuge the blood parasite has been responsible for reproductive failure in Canada geese (Branta canadensis; Sherwood 1968). If black fly problems reach such a scale in the Aleutians, the parasites might prove limiting to pelagic birds as well as to waterfowl. Winds, for which the Aleutian region is famous, constitute a limiting factor for obligate blood-feeding Simuliids and may control the severity of this problem.

Predatory Animals

The list of introduced animals that prey on seabirds is extensive. Often several animals have been introduced to the same island. For example, in 1951 Amchitka Island in the Aleutians supported populations of feral dogs (Canis familiaris) and cats (Felis catus), rats (Rattus norvegicus), and arctic fox. Their presence resulted from three of the usual sources of predator introductions: escape of pets, escape from visiting ships (and aircraft), and commercial introductions. Add introductions to control pests, such as that of the mongoose (Herpestes auropunctatus) to the Hawaiian Islands, and only one source remains—the desire of man to improve on nature. In the Aleutians this impulse has taken the more innocuous form of fish and plant introductions, such as rainbow trout (Salmo gairdneri) on Adak and Shemya, and trees (mostly Sitka spruce, Picea sitkensis) on every military base in the "Chain."

Rats appear to be the most commonly introduced predators on a worldwide scale. Ships furnish the traditional source of their introduction, but one of us (R.D.J.) has observed them disembarking from a military aircraft at Cold Bay on the Alaska Peninsula. These animals 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 percentage 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 peregrinus) 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 (Troglodytes troglodytes kiskensis) from Amchitka to predation by rats.

Many authors have mentioned potential rat damage, but few have quantitatively documented it. Imber (1974), however, provided data concerning the magnitude of rat predation 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 Polynesian and Norway rats that a petrel colony is endangered if invaded by a species of rat whose maximum weight approaches or exceeds 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) recorded predation by the Alexandrian rat (R. rattus) on ancient murrelets (Synthliboramphus 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 easternmost group of islands in the Aleutians, known as the Lissii or Fox Islands (Berkh 1823; Murie 1959). At the other end of the archipelago, 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 island 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 Company were of both species (Tikhmenev 1861). Initially both species were successful in developing insular populations, but in the long run the arctic fox proved the more successful. At Great Sitkin, Adak, and Kanaga, introduced 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 populations, the dark phase remained generally dominant at about 95%, but in some small islands with limited genetic stock (e.g., the Semichis) the proportion approached one to one (unpublished records of the Aleutian Islands National Wildlife Refuge).

By 1936, the Aleutian archipelago constituted 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, arctic foxes were introduced on almost every island from the Aleutians to Prince William Sound, and on some of the islands in southeastern Alaska. The Aleutian Islands National Wildlife Refuge maintained records from which the above figures are quoted, but though records of other islands' use for fur farms exist in the archives of the Alaska Game Commission, no record of the fur values was kept.

Murie (1959) assessed the influence of the foxes by examining 2,501 fox droppings collected in 1936 and 1937 from 22 of the Aleutian Islands. He reported 57.8% of the food items in these droppings was avian—48.9% seabirds. The result of his investigations was the adoption of new policies governing issuance of permits for fox farming in the Refuge. The essential feature of these policies was the revocation of certain existing permits, with a view to reserving the islands concerned for wildlife use. The decision proved academic, for fur prices declined until no market for Aleutian arctic fox pelts could be found. But the foxes remained.

The most obvious damage has been the nearly complete extermination of the Aleutian Canada goose (Branta canadensis leucopareia). It has vanished from its former nesting range in the Aleutian and Kuril Islands, except for Buldir Island in the western Aleutians (Jones 1963). Clark (1910) described this goose as extremely abundant on Agattu Island in 1909; however, foxes from Attu were introduced there in 1923, 1925, and 1929. Murie (1959) found "probably less than six pairs" in 4 days of traveling over the island in 1937.

In our main area of interest, cats appear to have been widely introduced, but we found no record of extensive predation on marine birds. Jehl (1972) attributed the extinction of the Guadalupe petrel to predation by cats, in combination with the destruction of vegetation by goats. Imber (1974) reported that "serious predation by cats upon a colony of gray-faced petrels on Little Barrier Island, New Zealand was observed in 1950. Since that time, the colony has become extinct."

Though feral dogs are reported present on islands in our area of interest, they do not appear to have significant influence on seabirds. On Attu Island, the pet dogs of personnel of the Coast Guard LORAN station are reported to take common eiders (Somateria mollissima).

Conclusions

Ecological consequences of animal introductions to islands are rarely well documented. Usually no thought is devoted to such consequences until redress becomes difficult or quite impossible. Many of the introductions stem from a period before ecological understanding, and the introduced animal has acquired the status of a native. The arctic fox in the Aleutians fits all of these conditions. Until we conducted a thorough search of the literature, some of it difficult to secure and written in several languages, the original status of this animal was not known. Its elimination, now under way on selected islands, is difficult and expensive. Rapid recovery of some avian species, including certain passerines, has been observed. However, ecological homeostasis is the product of evolution, and restoration in the Aleutians must follow that course. It is not likely to proceed rapidly to a point thought desirable by man. The accidental introductions of animals such as rats and black flies in the Aleutians constitute particularly irksome events because they cannot be reversed. The new ecology of Amchitka, from which the foxes have been removed, must evolve in the presence of these species. Its face will look very different than if they were not there. We would like to suggest a means by which such introductions may be prevented, but it seems likely that more, not less, can be expected.

Preventing the introduction of ungulates seems more likely to be successful, especially if the islands lie within a National Wildlife Refuge. Even this, however, becomes less certain with an expanding human population and, with it, demands for more land on which to produce food.

Legal restrictions have been suggested as a means to control or prevent introductions, but in the northern islands, little enforcement is likely. There is a phrase bearing on this, said to have governed human behavior in the early years of Caucasoid occupation of the Aleutian Islands, "Heaven is too high and the Czar too far away."

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