Of the many indicators that herald the coming winter in the Petersburg area, one of the most exciting to avid birders is receiving a phone call from a friend announcing, "The swans are back."
The Blind Slough/Blind River drainage is about 20 minutes south of Petersburg along Mitkof Highway. This is a major stopover area for trumpeter swans during spring and fall migrations and, according to Forest Service reports, the most important wintering habitat for swans in the entire Stikine area.
Swans are present from about mid-October to mid-April. Based on overflights of the drainage, peak numbers average around 80 to 90 birds in late November or early December. Winter populations vary from 41 to 68 with an average of 55 swans. Cygnets (immature swans) make up about 25 percent of the winter population.
A visitor to the slough would likely observe 20 to 30 swans during the peak of the season and 12 to 20 swans during the winter months. There are several convenient observation points. An 8-foot-by11-foot, three-sided observatory with shuttered windows was built by the Forest Service at Mile 16 in 1985. This observatory provides an exceptional opportunity to watch these magnificent birds in their natural habitat at close range without disturbing them. A handicapped access to the observatory was completed in 1999 and there are plans for major renovations to the site in the near future.
The bridge to Crystal Lake Hatchery adjacent to the Blind Slough Recreation Area at Mile 18 provides excellent views of the middle and upper slough. Swans also can often be seen in the intertidal area at Blind River Rapids, which can easily be reached by a quarter-mile long handicap accessible boardwalk trail at Mile 15.
It is easy to tell the birds that are passing through from overwintering birds. Because of the plant tannins in the water, swans that have been feeding in the slough for an extended period develop a characteristic light brown or golden caste to their heads and neck that contrasts greatly with the pure white of their bodies.
Blind Slough is noteworthy as one of the northernmost overwintering areas for trumpeter swans in North America. What makes this area so special? There are a number of factors that contribute to its ability to support swans and numerous other species of birds and wildlife.
Blind Slough has a considerable expanse of shallow open water with large quantities of aquatic vegetation. Large natural coho runs and returns of king and coho salmon to Crystal Lake Hatchery contribute many carcasses into the slough. The slow-moving water allows the carcasses to remain within the slough to provide food and nutrients over a much longer time period than would be possible in a fast-moving stream or river system.
An extensive grass flat interlaced with channels at the head of the slough provides warm water seepage, which keeps the slough open when most nearby lakes are frozen over. The area has been closed to all waterfowl hunting since the late 1970s and closed to motorized vehicles during the winter months since 1984. This additional protection undoubtedly makes the area more desirable to the swans.
During extremely cold winters the slough sometimes freezes over. When that happens, the swans will either move downstream to feed in intertidal areas or crowd into the mouth of Crystal Creek into the relatively warm waters of the hatchery outfall. If there is a prolonged cold period the birds simply leave and fly further south until they find suitable areas with open water and adequate food.
Blind Slough, while notable for its over-wintering swans, is also special in many other ways. In recognition of its unique characteristics, Blind Slough and its surrounding area is designated by the Forest Service as both a Recreational River and a Special Interest Area.
This multifaceted ecosystem provides for a diverse population of birds and outstanding avian habitat. In bird surveys conducted during 1990, a total of 102 species were recorded. Of these, seven species were rare to Alaska and an additional seven species were rare to Southeast Alaska.
From late June through November, Blind Slough and Blind River provide excellent viewing opportunities for large concentrations of bald eagles. Besides the swans and other birds, there is an abundance of watchable wildlife including deer, black bear, moose, mink, otters, porcupines, an occasional brown bear and much more. Of the unusual bird or mammal sightings on Mitkof Island, a disproportionate number are from this area.
During two recent trips to the slough in early November, I observed only three adult swans, but saw 15 different species of birds including approximately three dozen eagles, six species of ducks, geese, snipe, a belted kingfisher, and a great blue heron. Blind Slough is truly a natural history treasure within the Tongass National Forest
Barry Bracken is a semi-retired marine biologist and naturalist who operates a marine ecotour company in Petersburg. Contact members of Juneau Audubon Society at firstname.lastname@example.org.