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  Stockton, CA 95206
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Scott Wilson

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Stanislaus River Report


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Stanislaus River Basin and Calaveras River Water Use Program
Threatened and Endangered Species Report - March 1995
Bay Delta and Special Water Projects Division, CA Dept of Fish and Game

Aleutian Canada Goose

Branta canadensis leucopareia
Listed as Threatened by the Federal U.S. Fish and Wildlife Service

Life History

The Aleutian Canada goose is one of the smallest subspecies and is identified by a combination of morphological characteristics. As is the case with all Canada geese, they are sexually monomorphic or similar in appearance. The most noticeable identifying characteristic is the white ring collar which ranges between 5/8 and 3/4 inches in thickness on the majority of individuals. Ring collars may also appear on Cackler, Taverner's, and lesser Canada geese but are always thinner (between 0.13 and 0.38 inches) and often are incomplete. In flight, it is sometimes difficult to distinguish between Aleutian and Cackler Canada geese because the size and weight ranges overlap. Cacklers, however, have much darker breast feathers giving them a bluish-black appearance while Aleutian's breast feathers are gray to brownish color.

Although geese readily use artificial nesting structures designed by biologists, populations have declined partly because Arctic foxes were able to invade natural nest sites. Under natural conditions the geese nest on a firm, dry, slightly elevated site, near water and feeding areas which are relatively isolated and with good visibility from the nest (Granholm 1988). Nesting material is usually matted down grasses, rushes, or tules, but sometimes eggs are laid on bare soil or gravel. Between March and July a clutch, which ranges from two to nine eggs, are laid and a 27 to 28 day incubation period yields precocial (covered with down and fully active) young. Goslings stay close to their parents while both go through molting periods. After eight to nine weeks goslings are usually prepared to fly and assume adult behavior.

Aleutian Canada geese winter primarily in the Central Valley of California often stopping along the coasts of Washington and Oregon on their way south. California offers temperate climate, several federal and state managed waterfowl units, and thousands of acres of private agricultural land where grain and grass shoots are a readily available food source. Grains such as barley, wheat, oats, corn, and rice are preferred as food in the fall. Grass shoots in late fall to late spring are also desirable when rains stimulate such growth. From late February to early April these birds migrate back north to the Aleutian Islands to breed in a cool environment with a rejuvenated food supply.

Findings and Conclusions

The Aleutian Canada goose was listed as threatened in 1976 and the decline in population size has mainly been attributed to the introduction of the Arctic fox (Alopex lagopus). The Arctic fox was first introduced to the Aleutian islands in the 1830s so the pelts could be harvested. The last introduction occurred in 1930 (USFWS 1982). Avian predators, skunks, coyotes, red foxes, and weather contribute to lost nest sites, but Arctic foxes are an additive factor in reproductive failure.

Extensive tracking of the Aleutian Canada goose by USFWS personnel have shown that it is typical for a majority of the entire population of this subspecies to winter in the vicinity of two private ranches, the Faith and Mapes ranches; approximately 6,000 and perhaps as many as 9,000 birds in recent years. The Faith Ranch includes the south bank of the Stanislaus River for two miles upstream of the confluence with the San Joaquin River; the Mapes Ranch borders the Faith Ranch to the east.

BioSystems conducted surveys in February 1993 and from December 1993 to March 1994 for the Aleutian Canada goose for the SR-120 Oakdale Bypass Project and observed Aleutians in several areas north and east of the city of Oakdale. These areas included both pastures and ponds; some adjacent to the river and others a couple of miles away.

The study area as currently defined may not include much Aleutian Canada goose habitat, but the grasslands and ponds adjacent to the river represent potential, and in some cases, known habitat. Any project affecting the Faith Ranch and other areas upstream that are suitable will have a negative impact on this species and would warrant further surveys.