Saving the Last Stronghold for Waterfowl
April 22, 2004
By James K. Ringelman, Ph.D.
Ducks Unlimited, Inc.
The Prairie Pothole Region will mislead you. It’s flat by most standards, with few trees and even fewer people. It lures people into thinking it’s monotonous and uniform. But it’s all a deception. In truth, the region is one of the most dynamic ecosystems on earth, and it’s the dynamics that make it the “duck factory” of North America.
To understand the PPR, one needs to start with a brief lesson in geology. During their retreat 10,000 years ago, glaciers left behind huge chunks of ice mixed with rocks and other glacial debris. When the ice melted and caused the surrounding glacial material to slump, millions of shallow depressions were left on the land surface – depressions that would become the “prairie pothole” wetlands. Shallow and productive, these ponds teem with the aquatic invertebrate and plant foods needed by breeding ducks. They also provide plenty of elbowroom upon which territorial birds can space themselves during the breeding season. But the uniqueness of the Prairie Pothole Region extends beyond the wetlands themselves.
The climate of the region also created vast grasslands. The deep root structure of the grass in turn developed deep, fertile soils, which further enhanced the productivity of the wetlands. Ducks took nourishment from the wetlands, but evolved to nest in the grasslands, sometimes a mile or more from the nearest water. And the entire system was dynamic. Periodic droughts would dry up wetlands and cause the organic matter in their soils to decompose, releasing nutrients and providing a flush of fertility when the wetlands re-filled. Fire and grazing by bison would likewise recycle nutrients in the grasslands, promoting vigorous growth and creating a patchwork of habitat of differing heights and densities. It worked this way for several thousand years, until railroads, land grants, and farmers began to change the face of the landscape.
Fast-forward to 2003. The climate still plays a critical role in rejuvenating prairie wetlands. It also influences populations of wildlife, including mammalian predators, in a couple of ways: directly, by influencing the winter survival of mammals that must make a living in the region’s infamous cold and snow; and indirectly by influencing the moisture available to plants and, therefore, the overall productivity of the prairies. Biologists believe that as productivity declines during a drought. This translates into a decline in plant growth, insect populations, and small mammals such as mice and voles. As a result, with a reduced food base, predators either move on elsewhere to “greener pastures” or decline to lower population levels as their ability to raise young declines with fewer food resources. When the moisture returns to the prairies and the wetlands re-fill, predator populations are still depressed but duck populations rebound quickly – “get ahead” of the predators, so to speak. This persists for a couple of years until the predator populations “catch up” with the replenished food resources and begin to exert more pressure on nesting birds. These dynamics are normal. It’s probably what allowed the continental duck population to grow an astonishing 69% between 1993 and 1999. What’s not normal is the landscape-level destruction humans have wrought on the prairies.
Over 70% of the wetlands in the PPR have been drained or severely degraded, and the destruction continues. Within the U.S. PPR, wetlands continue to be lost at the rate of 33,000 acres annually. In many places, grasslands are under greater siege than wetlands. Eastern North Dakota has lost 73% of its native grassland, and even less remains in the PPR of Minnesota and Iowa. A similar loss is evident in prairie Canada, where the amount of cropland has increased 30% in just the last 25 years.
These losses have had dire effects on waterfowl by eroding the long-term capacity of the prairies. Wetland communities are less diverse and wetlands fewer in numbers, reducing the carry capacity for breeding ducks. New predators have colonized the region, and the nests of ducks and other ground-nesting birds are concentrated in the few remaining tracts of grassland. Consequently, in many areas nest success is inadequate to maintain stable duck populations, and hen mortality rates are high. Yet, despite these conditions, duck populations have continued to rebound. How? While most portions of the Prairie Pothole Region idle along producing ducks at or below levels needed to maintain populations, a few places allow ducks to successfully reproduce at the high rates needed to that sustain the overall population. These "source areas" for ducks are found in the landscapes that still retain the rich community of grasslands and wetlands that existed prior to European settlement. There is great urgency in conserving these natural, remaining habitats. Grasslands for Tomorrow is Ducks Unlimited's premier conservation initiative to protect these last strongholds for breeding waterfowl.