Feeling The Heat
November 03, 2010
Global warming affects migration, nesting.
Wyoming's dark-goose season closed on Feb. 9, and my partner, Dennis, and I thought it was appropriate to commemorate the event with one last hunt. Dennis said he'd drive, so I met him at 4:30 a.m., which gave us a few extra minutes to figure out how we were going to get a pick-up load of decoys in the back of a Suburban and still have room for Sky, the Lab. On the fourth attempt, Dennis put his shoulder to the back door and leaned into it like a blocking sled. The latch made an equivocal snick, but the door stayed shut.
"Good enough," he pronounced. "Let's go."
It was a familiar drive: 60 miles north on U.S. 85 out of Cheyenne, Wyo., down off the Goshen Rim into the Platte River drainage, then 15 miles of gravel road to the marsh.
I've had some adventures on that road. It crosses the highest part of the High Plains, more than a mile above sea level, a part of the world that bears a striking resemblance to the Arctic tundra, especially during the winter. I've seen drifts that covered the delineator posts, winds more than 80 miles an hour and ground blizzards that blotted out everything beyond the hood of my truck, when the horizontal snow beating on the windshield made it seem like I was driving 60 mph when the speedometer showed five.
I've watched a couple of cars follow a semi right into the ditch because the drivers couldn't find the road. I've made it home in four-wheel drive, low-range, chains on in back, pushing snow with the bumper and thanking the angels who watch over waterfowlers and other fools traveling the plains in the teeth of the storm.
As we cruised through the blackness, I smiled ruefully, because even in February, no snow covered the highway or the wheat fields on either side. Every 10 minutes or so, a patch of white loomed in the ditch, a relict drift from the one snowfall we'd had, hardened to concrete by the wind and a procession of chinooks and cold fronts.
We got to the marsh about 6 a.m., loaded the decoys on a toboggan and headed toward the windward side. Dennis paused.
The small talk of a bunch of mallards rose out of the dark. Up ahead, I could make out the muted conversation of a small bunch of geese just waking up. It struck me as strange that the birds were roosting on this shallow wetland, which I was sure had been frozen solid for weeks.
Another 100 yards brought us onto one of the dikes. The overcast was lightening in the east, and I could see the mirror reflection through the bulrush -- open water. I thought of the shells and full-body decoys we had with us.
I'd brought some floaters, too, thinking I'd cut a hole in the ice for them. Now we'd have to go around to the north side and set up on the flats where we could combine the dry-land decoys with the floaters. Open water on February 9.
We found a spot, set up the spread, and then laid out in the decoys with camo covers and some local vegetation over us. At first light, the ducks got up to stretch their wings. They were safe, of course -- the season had closed three weeks earlier, just about the time the late mallards had started to show up with a couple pairs of pintails mixed with the greenheads. It seemed these flocks were leaning north already. Then, a pair of ducks dropped into the water on my left. Widgeon. The drake was already April bright and tended his mate with the intensity of a bull elk in rut.
As we waited for geese to make a mistake (they never did), I pondered the signs of the season parading by me. Spring was coming early on the Wyoming plains. These are the kinds of observations climate scientists call "anecdotal," and they take great pains to stress that one or two changes in one or two places don't provide much evidence for long-term change in the world's climate. I'm sure plenty of people from Bismarck to Baltimore who survived the rigors of last winter would be happy to provide anecdotes to contradict mine.
But I'm not alone in my experiences. About the time I was waiting for my last goose, the National Audubon Society released a preliminary report analyzing information from the organization's Christmas Bird Count. The count has been an annual activity for local Audubon chapters since 1900. Each chapter picks a day in late December or early January and gathers its members for 24 hours of hard-bitten birding.
At the end of the exercise, members pool their observations and the resulting list of species and the number of each species sighted is submitted to national headquarters. Since the mid-1960s, scientists at Audubon think the methods used in these counts have been standardized enough to provide a quantitative estimate of bird distribution and numbers across the continent, a snapshot of bird life on the wintering grounds.
The Audubon analysis shows average January temperatures in the United States have increased by more than four degrees Fahrenheit in the past 40 years. The authors of the study considered 305 bird species, tracking the average center of their winter distribution over time. Of the 305 species, 177 showed a significant shift to the north, while 79 showed a significant shift to the south. The authors estimated the overall northward shift amounted to 34.8 miles in the 40 years covered by the study.
Most ducks follow the general trend. The authors estimated the center of the winter range of the gadwall has moved 149 miles north in the past 40 years. The black duck has moved north 182 miles. Cinnamon teal, 159 miles; greenwings, 157 miles. The pintail, 91 miles.
The ring-necked duck, 219 miles. The lesser snow goose, 217 miles. The canvasback is an exception to the pattern -- it has moved the center of its winter range about 74 miles south. The greater scaup has moved south about 136 miles.
For those of us who hunt to the south of North America's duck factories, this analysis confirms what we've been seeing over our decoys for the past 50 years -- on average, migrating ducks seem to arrive later and in smaller numbers than they once did. The bad news is this short-stopping phenomenon isn't just the result of changing regulations, shifting farming practices or the creation of new impoundments. It might be driven by a fundamental change in climate.
Another recent technical report suggests climate change might also affect ducks on their breeding grounds. In a paper for Bioscience, Carter Johnson and several colleagues reported on an effort to predict future conditions in the prairie potholes of the north-central U.S. and southern Canada. Johnson compared conditions over the past century with the changes in climate predicted if the temperatures on the northern prairie increase by 3 degrees Celsius and precipitation patterns change, as well.
According to Johnson's model, a 3-degree increase in temperature with no change in precipitation would shift the best climate for pr
airie ducks to the eastern fringe of the pothole country. The optimum duck production area would be less than half of the optimum area in the past.
A 3-degree increase in temperature with a 20-percent decline in precipitation would move the best duck-producing climate into a small part of north-central Iowa. The size of this optimum zone would drop by more than 80 percent from its size in the past. The model also suggests that, regardless of the pattern of temperature and precipitation, warming will do little to improve the nesting conditions in the prairie parklands on the northern edge of the pothole region.
Climate isn't the only variable affecting duck production, Johnson points out.
"Historically, the eastern Prairie Pothole Region and northern parklands served as a safe haven for waterfowl during periodic droughts," he writes. "Today, however, options are limited, because more than 90 percent of eastern Prairie Pothole Region wetlands have been drained for agricultural production."
If the best climate for duck production shifts to the east over the next century, it will come to an agricultural landscape almost devoid of wetlands and nesting cover. All the rain and snow in the world won't do much for nesting ducks if there's no habitat to go with the water.
In its last report, the Intergovernmental Panel on Climate Change estimates the average annual temperature in the pothole region will rise 3.5 to 4 degrees Celsius between the 1990 and 2090. The panel also expects precipitation to increase by 5 percent to 10 percent over that time, with all of the additional precipitation coming in the winter. If these predictions turn out to be accurate and the Johnson model for the pothole region also proves true, duck production in the potholes will drop drastically.
It's easy to hope the breeding effort will simply move farther north into the boreal forest of central Canada. But the boreal forest isn't as productive a landscape as the prairies.
Most of the continent's lesser scaup have traditionally nested in the boreal forest, and the long downward trend in their population suggests the forests have developed their own problems as waterfowl habitat. It's unrealistic to expect puddle ducks in the forest to produce as many young as they once did on the prairies to the south. And the condition of northern waterfowl habitat will probably deteriorate over time -- a warming climate will almost certainly mean more human activity in the boreal forest as well, a variety of disturbances that will probably undermine the quality of nesting habitats in the region.
The climate trajectory we've set for ourselves almost certainly means fewer ducks, and the ducks wintering farther north. We can't dodge the effects of the carbon dioxide we've already pumped into the atmosphere, but we can take steps to limit the carbon dioxide we produce in coming decades.
The ducks are already doing what they can. When will we?