November 03, 2010
When pointing at predators, it's hard to tell the good guys from the bad
It wasn't much of an island, a pile of cobbles half a mile off shore with a thicket of nettles and one scraggly elm tree. For nesting ducks, the advantage was obvious--no foxes, skunks, coons or ground squirrels to eat eggs and threaten hens--but it was a long swim to the cattails and bulrushes.
Bob and I paddled up just as a gadwall hen gathered her family for the trip. The youngsters were hardly 24 hours out of the shell, tiny balls of down that bobbed around their mother like fluffy yellow ping-pong balls. The hen took a bearing on the nearest point of the mainland and struck out.
They got about 30 feet. A ring-billed gull swept down and plucked the trailing duckling out of the water. A second gull followed the first, and a third, and a fourth. Then there was a break in the assault. What was left of the family swam furiously out onto the open water, and as they disappeared into the swells, I thought I could see four ducklings still following the hen.
Even on a bright June morning with the prairie breeze caressing the grass, such moments are a grim reminder of the darker side of life, and for anyone who has followed the affairs of prairie ducks, they are also a reminder of the most divisive issue in waterfowl management: predator control.
As the data on predation and ducks have emerged, waterfowl managers have struggled to find a way to improve nest success and duckling survival. There are two camps. One favors the direct approach--kill the predators that are killing ducks and destroying nests. The other focuses on habitat--if there is enough good cover, they argue, there will be enough ducks.
The argument between advocates of predator control and habitat is driving a wedge deep into the community of waterfowl conservationists. There are hunters, waterfowl groups and even a few biologists on each side. Over the years, I've made no secret of my position on the issue. I don't support widespread predator control. I still believe more habitat is the best way to produce harvestable surpluses of ducks. In this column and the next, I'll explain why.
Coyote as good guy? Protecting nesting ducks is a lot more complicated than killing skunks and raccoons. Where coyotes reside in healthy numbers, smaller predators like ground squirrels and fox decline, resulting in increased duck nesting success.
First, the ecology of ducks and their predators: Most people with an interest in waterfowl have some notion of how we got them into trouble. In the prairie pothole region of the northcentral U.S. and southcentral Canada, the continent's duck factory, we've drained 40 percent of the wetlands that dotted the landscape when we first arrived. Many other wetlands have been badly degraded. In other parts of the country, losses have been much worse--Iowa, for example, has lost 90 percent of its original wetlands.
We've also gutted the prairie uplands. More than 99 percent of the continent's tallgrass prairie has been eliminated. A large portion of the mixed-grass prairie to the west is also gone, and even the shortgrass prairies of the high Plains have lost significant acreage to the plow. The native grasslands that are left are often grazed year-round and/or hayed, reducing the cover available to ground-nesting birds, including prairie ducks. The hens that are left pack into the remaining cover, concentrating their nests and leaving themselves more vulnerable to catastrophic droughts and floods, and more exposed to predators.
While we were busy transforming the prairie landscape, we also funded a successful campaign to extirpate the gray wolf and an extensive poisoning and trapping program thinned populations of coyotes. This effort against the large wild dogs had an unexpected consequence--it allowed red foxes to move south out of Canada into the heart of the duck factory for the first time.
The new foxes caused some special problems for prairie ducks. A piece of land that once supported a pair of coyotes and their offspring may support three or four pairs of red foxes, and the foxes are more likely to focus on small game like ducks and their eggs than the coyotes did. It's a sad irony that one of our most challenging problems in duck management was actually caused by predator control.
Over the last 40 years, research has shown that a piece of country dominated by foxes will have significantly lower duck-nesting success than a similar piece of ground dominated by coyotes. Another landmark study, reported in 1995, clearly demonstrated the reverse--duck-nesting success in areas dominated by coyotes was almost twice as high as in areas dominated by red foxes. The combination of scientific work suggests that a coyote recovery program would do as much for ducks as an effort to control foxes and skunks.
In the past, our efforts to control predators have been painfully nonspecific. Our desperate attempt to eliminate coyotes and red foxes almost led to the extinction of the northern swift fox, the tiny, burrow-dwelling native of the shortgrass plains. The swift is listed as endangered in southern Canada, and three years ago, the U.S. Fish and Wildlife Service decided that listing the swift as threatened south of the border was "warranted but precluded."
The same could be said for the Franklin's ground squirrel in the tallgrass systems east of the Missouri River. This unlikely predator routinely eats duck eggs and is a primary target of trapping efforts in North Dakota. Unfortunately, the Franklin's ground squirrel has declined with the decline of tallgrass prairie in North America. Alberta gives the species an "undetermined status," pending further study of populations in the province. In Wisconsin, it's a species of "special concern." It's considered rare in Illinois. The International Union for the Conservation of Nature lists the Franklin's ground squirrel as "vulnerable." With the advent of CRP and the grassland reserve, the species is in no immediate danger in the remainder of its range, and I hope waterfowl enthusiasts never have to explain how a program designed to protect nesting mallards put another prairie native in jeopardy.
Then there's the badger. Considered common in much of the Midwest, badgers eat duck eggs and nesting hens along with gophers and ground squirrels. They've been trapped as part of predator control efforts in the Dakotas. But the badger is struggling in parts of its range--it's listed as a mammal of "yellow A status" in the province of Alberta, suggesting that trends in badger population on the northwestern edge of the species' range aren't encouraging.
How do we avoid some duck predators while catching and killing others? Clearly, we don't use poison or Conibear traps. After a while, most animals get suspicious of live traps, and if we do accidentally take a swift fox or so
me other off-limits predator in a live trap, somebody has to figure out what to do with him.
The crazy thing about controlling these smaller mammals is that, given the chance, they do a fairly good job of controlling each other. If there are lots of ground squirrels and mice around, foxes, skunks, raccoons and badgers eat them. Research suggests that ducks do better in cover that produces lots of mice, voles, amphibians, insects and other small prey. A wider variety of food keeps medium-sized predators from focusing on nesting ducks.
The call for widespread predator control focuses on ground-based predators, especially the red fox, striped skunk, raccoon, badger and Franklin's ground squirrel. There seems to be an expectation that, if we can just reduce the numbers of these predators, prairie ducks will prosper indefinitely. Short-term studies suggest that this is true--fewer foxes and ground squirrels result in higher nesting success for ducks. But hard ecological experience suggests that these benefits are likely to be short-lived. High densities of prairie ducks in limited habitat will attract more predators. Well-fed predators will raise more young, and those young will learn to hunt ducks and their eggs.
If we manage to control the predators that are causing the bulk of the damage today, there's a good chance that other predators will recognize the opportunity and take advantage of it. Twenty years from now, the villain may be the common crow, magpie, blue jay, great blue heron, or northern harrier. Up until now, avian predators haven't had much effect on ducks in the Dakotas, but they're a significant problem in the shortgrass prairies of Alberta.
Our past campaigns against predators have caused more problems for ducks than they have solved, bringing new predators into the pothole country and encouraging others that were already there. Do we understand the relationships between predators and prey better now than we did 60 years ago? I wonder. I think a renewed offensive against predators could cause unwanted side effects.
In 1933, Aldo Leopold, the father of modern game management, said: "To keep every cog and wheel is the first precaution of intelligent tinkering." It's worth remembering.