Weekly Bird Notes - Canvasbacks

Large rafts of winter waterfowl get me excited. With scope in hand, I can spend hours watching them follow food sources around a bay, perform courtship displays, and pop up to the water’s surface after foraging. The birder in me also likes to scan for rare and unusual species. Luckily for me and other birdwatchers in Vermont, it seems that unusual birds are rarely lacking in Lake Champlain, the Connecticut River, or Lake Memphremagog, Vermont’s primary hangouts for congregating waterfowl. This week, a pair of Canvasbacks has been frequently observed amongst a raft of Common Goldeneye in Shelburne Bay on Lake Champlain.

Canvasbacks are so-named for their whitish backs, the color of undyed canvas. Their white back contrasts sharply with their chestnut-colored head, and they are further distinguished from other diving ducks by their sloping forehead and bill. They are only likely to be confused with Redheads, a smaller diving duck that lacks the sloped forehead and has a black-tipped blue bill with a gray back.

Canvasbacks are among the least abundant duck species in North America. They breed along the deeper ponds, marshes, and potholes from Alaska and the Northwest Territories south to Colorado and Minnesota. They are omnivorous, consuming a mix of buds, roots, tubers, and insect larvae. During years of drought, when the ponds and marshes dry up and there is less food available, they will delay breeding, avoid breeding altogether, or move further north. A decreased rate of breeding, coupled with lower breeding success resulting from parasitizing Redheads laying eggs in Canvasback nests, helps explain their low overall population size.

Sensitivity to changes in available food resources, especially of plant tubers, has resulted in Canvasbacks changing their migratory and wintering behavior over the last 50 years. When food supplies were eliminated due to sedimentation and pollution on their traditional migratory stopover sites in Minnesota and Illinois, they utilized newly created habitats in impoundments along the Mississippi River. Their current migration routes see annual changes in abundance, partly in response to fluctuations in food availability. Large flocks overwinter in the coastal waters of the U.S. and in the interior south, where they historically used brackish waters with an abundance of food, but now adjust habitat use based on weather, habitat availability, and the level of human disturbance.

Other Sightings

A male Redhead was observed in the New York waters of Lake Champlain in Westport on January 6. A rare Three-toed Woodpecker was observed at Moose Bog in the Northeast Kingdom on January 5, the same location one was observed last winter. Although not highly unusual, a Great Blue Heron in Grand Isle on January 4 may be an indication of more open water and bare ground, leading to additional sightings of herons, kingfishers, buntings, larks and the like.

The official eBird stats were released this week. A record 6,047,650 birds were reported on 442,985 checklists submitted in 2007. Vermont ranked 14^th overall, 12^th in the U.S., for number of checklists submitted (10,755), possibly the highest per capita rate. Happy birding in ‘08!

You can explore all the birds reported last week in Vermont and add your own sightings at VT eBird.