Canvasbacks are proof of backwater recovery
BROWNSVILLE — Mississippi River backwaters are icing over, which means the canvasback ducks and tundra swans will soon be out of here.
Their presence this year, however, told a story of a recovering river backwater system. The two species are especially good indicators of how well those backwaters are doing biologically. If the birds have food and undisturbed places to rest, they come and they stay as long as they can.
This year, indications are they came and stayed. Though use days and total populations counts are not complete, the aerial count a few weeks ago showed about 40,000 swans and about 165,000 canvasbacks in pools from Wabasha down into Iowa. With ice forming in the past week, many of them have left.
In fall, river backwaters are critical for those two species. In most years, more than half the canvasbacks in the world use the refuge before either heading further south or east to Chesapeake Bay. Swans are also heavy users of the river before heading to Chesapeake.
They especially like wild celery and arrowhead. "If those plants aren't here, you aren't going to have canvasbacks and swans," said Jim Nissen, manager of the La Crosse District of the Upper Mississippi River National Wildlife and Fish Refuge.
Just how critical the food is was shown in 1989 and 1990, when heavy summer algae blooms nearly wiped out any celery and other submerged plants. Peak canvasback use on Lake Onalaska north of La Crosse, went from about 30,000 in 1998 to nearly zero. After celery recovered, it has shot up and hit nearly 100,000 in 2002.
Some of the reasons for the good food supply was evident a week ago at the overlook just south of Brownsville. From that spot it was easy to see swans and, earlier in the season, the canvasbacks. Several islands were built there over the past several years to slow the wind that riles up and dirties the water. With dirty water, it's hard for the vital water celery to grow in deeper water, or arrowhead in shallower water.
Similar projects have been done in several other major backwaters, such as Weaver Bottoms south of Kellogg.
Another reason for heavy waterfowl use is what Nissen and Kevin Kenow, a U.S. Geological Service research wildlife biologist, didn't see — boats. The service has asked boaters to voluntarily avoid key loafing areas, especially on Lake Onalaska north of La Crosse, Kenow said.
With new motors, boaters can roar through shallower waters without jamming propellers or smashing lower units, he said. Just one boat in the wrong place can send thousands of canvasbacks fleeing — and they might not come back to prime feeding areas, no matter how great the food supply might be.
Both species once used lakes and marshes in western Minnesota, the Dakotas and eastern Wisconsin as their key stops where they bulk up on food before continuing their migration. When those places were degraded by human activity, the birds found the backwaters.
Canvasback numbers were once so low that hunters weren't allowed to shoot any on the river, and only one in some parts of Minnesota. This year, the limit was two.
But that doesn't mean canvasback populations are safe, Kenow said. Like all wildlife, they have a life cycle and need good conditions throughout the year. One weak link can severely hurt numbers.
In the case of canvasbacks, it's water on breeding grounds, he said. They nest in reeds or cattails, and ducklings quickly go into the water to feed on invertebrates. "That protein is the key thing for the young ducklings," he said. Later, they feed on vegetation. Without water, reproduction can crash, he said.
A Ducks Unlimited survey in southwest Manitoba found nesting success varied from zero in 1997 — a dry year — to 70 percent in 1978, a wet year.
The past few years have been good, with a breeding population of 787,000 this year, 37 percent higher than the long-term average, according to a service report. In 2008, it was about 500,000.
Though breeding populations fluctuate a lot, the number of canvasbacks using the Upper Mississippi refuge is slowly growing, the USGS found. In 2009, it was more than 400,000; this year's numbers haven't been compiled yet.
Swans didn't begin using the refuge until the late 1970s, Nissen said. Now, they can peak at 50,000 birds or more.
In the next few years, habitat could improve even more. The service, Corps of Engineers and Minnesota and Wisconsin departments of natural resources are cooperating to lower river water levels in summer. With more light, celery and arrowhead thrive. When levels are raised back up in fall, the migrating canvasbacks and swans can feast on them.
At least until the ice sends them on their migratory way.