- photo by Michaelfurtman.com
Crunching the Numbers
Our understanding of wetland loss suggests that the duck factory could once support three times as many breeding ducks as it does today. To keep it simple, let's assume that the number of ducks breeding outside the prairies has not changed. We'll also assume that recruitment in these areas hasn't changed. In addition, we know that the largest fall flights occur in years when the prairies are universally wet, and that up to two-thirds of all ducks are counted on the prairies in wet years.
To estimate how big the fall flight might once have been, we can use modern-day duck populations and work backward. Let's assume that there are 50 million breeding ducks (total ducks, not pairs) distributed across the United States and Canada. It's been a very wet spring and 33 million of these ducks have settled on the prairies, while another 17 million can be found in Alaska, the western boreal forest of Canada, and areas outside the TSA. Given such conditions, we may have a fall flight of 100 million ducks, which we will use as our benchmark for modern day duck populations when the prairies are wet.
Now turn the clock back to 1805, when Clark was trying to get some sleep along the Columbia River. Assuming that the prairies have also been very wet, we have 100 million total breeding ducks (including both paired and unpaired birds) on the prairies. Duck numbers outside the prairies are unchanged at 17 million. This means that 200 years ago, we had 117 million breeding ducks compared to 50 million today (or 2.3 times as many ducks). At face value, this translates into a fall flight of about 230 million birds (2.3 x 100 million).
But we haven't yet accounted for changes in recruitment. Let's assume that recruitment on the prairies was twice what it is today, mostly due to higher nest success and duckling survival. Not only have we tripled the number of ducks on the prairies; they're twice as successful at producing young. We'll spare you the math, but this pushes our presettlement fall flight estimate to around 430 million birds, even if we assume that duck breeding populations and recruitment outside the prairies have not changed.
It's important to recognize that fall flights in excess of 400 million birds were probably rare. Our suggestion that the prairies could once support 30 million breeding pairs or 100 million total ducks assumes that most temporary and seasonal wetlands held water. In many years, large parts of the prairies were dry and the full carrying capacity of the duck factory would not be realized. Moreover, these incredibly wet years would have to be preceded by years of very good production if there were to be enough ducks to fill all those wetlands. Still, it's fun to imagine what it would be like to experience such a fall flight while sitting in a duck blind. We doubt that you'd complain about the noise.
Dr. Mark Petrie and Dr. John Coluccy are directors of conservation planning at DU's Vancouver (Washington) and Great Lakes/Atlantic offices, respectively.