Ducks in a Changing Climate

© Michael Furtman

By Mike Anderson, Ph.D.

No matter what you've thought about climate change, much has changed in the past two years. Conversations among waterfowl managers, scientists, and many sportsmen and -women have shifted from "Is it happening?" to "How can we adapt to the changes unfolding?"

In 2007 the Inter-Governmental Panel on Climate Change (IPCC) issued four authoritative reports about how Earth's climate has changed. They also offered a range of predictions about the future and advice about responding. In a global nutshell, patterns of temperature and precipitation have changed significantly over the last 150 years, but in ways that differ among geographic regions. Change is likely to continue for many decades or longer. We can expect a future that on average will be warmer and, depending on locale, wetter or drier than in the recent past.

The effects of these changes on North American waterfowl habitats, Ducks Unlimited's conservation work, and the fortunes of waterfowl hunters could be profound. Consequently, DU is taking steps to keep informed and, wherever possible, incorporate climate science into its conservation planning.

How Could Climate Change Affect Ducks?

While climate change may affect waterfowl directly (e.g., by altering timing of migration), more serious impacts could occur through effects on habitat. Projections for the next 100 years indicate warming in most areas, changing patterns of precipitation, accelerating sea-level rise, declining snowpacks, and increasing frequency and intensity of severe weather. Consequences for waterfowl habitat could include changes in the timing and duration of when wetlands are wet, changes in land use, northward expansion of invasive species, and greater challenges for water management.

DU's International Conservation Plan has identified North America's two most important waterfowl breeding areas—the Prairie Pothole Region and the western boreal forest—as our top priority conservation regions. Next in importance are the continent's key waterfowl wintering areas: the Central Valley of California, Gulf Coast, and Mississippi Alluvial Valley. Waterfowl could face significant climate-related impacts in these high-priority areas.

In the Prairie Pothole Region, for example, average temperatures have increased over the past century, and all global climate models predict further warming and a reduction in average soil moisture in this region. Expected ecological changes include fewer wetlands on average, shorter duration of flooding in wetlands, and greater annual variability in surface water—in short, both deluge and drought.

Rapid alternation between wet and dry years might actually be helpful to ducks, whose mobility allows them to respond more rapidly to changing conditions than can their predators. Prolonged drought would be another matter. Thus, future patterns of year-to-year variability in precipitation will be important to waterfowl.

But just as important is what will happen to prairie agriculture. Agricultural practices such as grazing and haying that leave grassland intact provide habitat for nesting waterfowl and other wildlife, and conserve accumulated carbon in prairie soils. In contrast, intensive annual cropping (e.g., for grains and oilseeds) is associated with lower waterfowl breeding success. Agricultural experts are divided about how prairie agriculture will change in the decades ahead, but one recent analysis by Agriculture Canada suggests that new areas of Alberta and Saskatchewan may become suitable for small-grain production in the future, which would be a negative development for waterfowl habitat. 

The vast western boreal forest of Alaska and northwestern Canada may be among the regions most affected by climate change because of the greater temperature changes expected at high latitudes. Predictions include longer ice-free seasons, melting permafrost, increasing frequency and perhaps intensity of fires, and northward range shifts by plants, animals, and forest pests. Recent studies in Alaska and Siberia discovered that melting permafrost has contributed to drying of small wetlands and reduced habitat quality for ducks like scaup and scoters.

The biggest obstacle in predicting impacts of climate change on boreal waterfowl is our meager understanding of the basic ecology of boreal wetlands. We know little about what limits waterfowl populations in this remote region or the wetland food webs on which ducks depend. This is a serious knowledge gap because while several boreal duck species (scaup, scoters, and wigeon) are declining, resource development is expanding and northern climate is changing.

Along the Gulf Coast, wintering waterfowl could suffer substantial habitat losses. Oceans are rising due to thermal expansion and melting land ice. In 2007 the IPCC projected that with a global temperature rise of 3 degrees Celsius (5.4 degrees Fahrenheit)—a middle-range scenario—30 percent of the earth's coastal wetlands would be inundated by saltwater. Vulnerability of coastal wetlands varies from place to place. In south Louisiana, where about 40 percent of America's brackish and freshwater coastal wetlands are found, seasonal flooding of the Mississippi River historically created a series of deltaic wetlands. Today, dams on the upper Mississippi River have reduced sediment load by about 50 percent, and the construction of levees has greatly reduced flooding. Less sediment is available to build new wetland habitat, so coastal marshes are unable to keep pace with sea-level rise. During the past 70-80 years, more than 750,000 acres of coastal wetlands in southeastern Louisiana have already been converted to open saltwater.

In the Central Valley of California, higher temperatures are predicted to cause more precipitation in the Sierra Nevada Mountains to fall as rain rather than snow. More rapid runoff and earlier snowmelt would lead to higher winter flows but also increased competition for water during the summer. Refuges, duck clubs, state wetlands, and rice fields all depend on allocations of California's managed water. If future winters in the Central Valley are indeed wetter than today, waterfowl may benefit. But the value of this flooding would depend on land use. If rice production declines (because of rising irrigation costs, for example), then winter flooding of agricultural land would be of little value to waterfowl. Reduced summer runoff also might contribute to concentration of toxic chemicals in estuaries to the detriment of wintering diving ducks.

Future impacts of climate change are less certain in the Mississippi Alluvial Valley. Scientists know the extent of winter flooding in the region affects body condition and winter survival of mallards. Presently, however, climate models offer contrasting predictions about future river flows, leaving us with little ability to predict flooding patterns.

What Should Conservationists Do Now?

Global climate change poses difficult challenges for conservation planners because of the scale and complexity of the problem, the long time required to learn about impacts, and the uncertainty associated with predictions about future conditions. In the long run, reducing greenhouse gas emissions seems prudent for reducing losses of waterfowl habitat, and DU is taking steps to assess and improve its own carbon "balance sheet."

We must also consider strategies to help species and ecosystems cope with changes that are inevitable. The immediate challenge for DU is to judge what adaptations are reasonable now, even if we are unsure, and, second, what should be done to position ourselves to make even better decisions in the future. Several actions seem prudent:

1) Manage for resilience. Waterfowl habitats almost everywhere have been affected by human development, so any effects of climate change will be imposed on top of existing pressures. Reducing existing stresses on wetlands (e.g., nutrient loading, toxic chemicals, filling, drainage, soil erosion, urban encroachment) and associated uplands (e.g., overgrazing, intensive tillage) should reduce vulnerability to climate-induced changes and may be the single most achievable thing that we can do today to help prepare for a warmer but uncertain future. Increased variability and intensity of weather are expected too. Restoring or protecting complexes of wetlands of varying permanence and striving to restore habitats across a wide geographic area may help hedge against variable moisture conditions.

2) Encourage cross-jurisdictional planning where geographic shifts in ecosystems are likely. For instance, coordinated planning for the provision of wintering habitat in the Mississippi Valley and Gulf Coast regions seems prudent and is under way by conservation partners in these regions. Protecting habitat at the northern fringe of the pothole region where lengthening growing seasons will favor agricultural expansion into forested landscapes is another such action. DU will also support efforts by the national wildlife refuge system and by neighboring states and provinces to cope with species' range shifts and changes to waterfowl habitat. We need to challenge conventional thinking about the most useful geographic areas, time scales, and partnerships for executing conservation plans.

3) Protect coastal wetlands from sea-level rise. Because it takes centuries for air and ocean temperatures to equilibrate, the atmospheric warming that has occurred already guarantees that sea level will rise for a long time. Everywhere wetlands are threatened by sea level rise, coastal zone regulations and development plans should be examined for opportunities to enable landward migration of wetlands (see sidebar). Restoration of the Mississippi River's historic sedimentation processes may help restore wetlands on a large scale in southeastern Louisiana. In this way, efforts to restore rivers and floodplain habitats in the Midwest can benefit coastal wetlands by restoring historic river flooding and sedimentation downstream. 

4) Seek opportunities to tie habitat conservation to carbon markets. The public may support added wetland restoration efforts where multiple benefits of nutrient reduction in water, flood abatement, groundwater recharge, carbon sequestration, and wildlife habitat can be realized simultaneously. At the state/provincial, federal, and international levels, DU's science is already informing public policy discussions that seek to protect the ability of grasslands, wetlands, and other natural systems to absorb and store carbon, and that support market-based tools for conservation of environmental goods and services. Additional research is required to determine how different types of wetlands capture greenhouse gases and how wetland carbon stocks respond to drainage, flooding, nutrient inputs, or restoration. An obvious first step, however, is simply protecting intact wetlands and native grasslands to avoid additional release of stored carbon.

5) Employ adaptive management and increase research and monitoring work to improve management decisions. Earth's climate is changing. Species and ecosystems will respond to these changes, and humans will continue to manage natural resources in the face of these changes. This presents difficult choices because we cannot know the full impacts of our management actions, resources are limited, and many stakeholders are involved. What we require, therefore, is a commitment to learning as we go and applying what we learn to improve future management decisions. We need to design monitoring programs that explicitly evaluate different climate-change predictions, sample over sufficient space and time, anticipate the possibility of unexpected changes, and are affordable and sustainable. 

6) Be nimble; respond to new knowledge, threats, and opportunities. One specific challenge for waterfowl and wetland managers is that climate models were built to work at large geographic scales. Downscaling model predictions to smaller regions, such as subdivisions of the Prairie Pothole Region, would be highly desirable for conservation planning, but this is not well supported by current models. Emerging trends in agricultural land use will merit special attention.

Another immediate concern is the ability of agencies to detect shifts, should they occur, in a species' population dynamics that could affect levels of sustainable harvest. Those responsible for managing hunted populations must be able to assess impacts and adjust harvest strategies in response to changing conditions.

7) Manage water wisely. Maintaining managed water is often an important part of maintaining wetland systems, and the needs are varied. In Louisiana, water-management plans that better resemble historical processes that rebuild Mississippi Delta wetlands are needed. In the Prairie Pothole Region, the likelihood of drier conditions should persuade stakeholders to develop less water-intensive agriculture, securement of long-term water rights and capacities, and holistic watershed plans. In California, the future will be all about the supply and management of transportable water.

None of these individual actions can offset altogether the expected effects of climate change on waterfowl, but they are concrete, low-risk steps that we can take now. They will be good for wetland conservation and inform future management choices whatever the extent of climate change. It's time to act; delay will only make adapting more  difficult in the future.