Every year, over 10 million ducks migrate north to their nesting grounds in North America’s Prairie Pothole Region, but the landscape that welcomes them has altered. Weather fluctuations and agricultural operations have altered the pothole-dotted natural grasslands that ducks have relied on for thousands of years.
As a result of these changes, certain duck populations have increased while others have declined. Nesting date is a crucial element in deciding winners and losers in the Prairie Pothole Region, according to a new study performed by a Penn State-led research team.
According to study leader Frances Buderman, assistant professor of quantitative wildlife ecology, waterfowl nest in a variety of habitats in the region, including idle grassland, crops, and over water.
“But when early nesting ducks arrive in the Prairie Pothole Region, many fields are covered in debris left from the previous fall’s harvest, mainly stubble from cereal grains,” she said. “Although this habitat looks inviting, the eventual replanting of these fields, as opposed to leaving them fallow, makes the ducks more vulnerable to predators and often results in their nests being destroyed by agricultural activities such as tilling and planting.”
The U.S. Fish and Wildlife Service and the Canadian Wildlife Service have monitored spring population abundances for North American waterfowl using the Waterfowl Breeding Population and Habitat Survey since 1955 producing one of the largest datasets on vertebrate populations in the world.
These ducks are adapted to nest in mixed-grass prairie, and as that wild habitat has largely been replaced by agriculture in the Prairie Pothole Region, the birds are confused, Buderman explained.
Early-nesting ducks that don’t nest in cropland, and diving ducks such as canvasbacks, nest over water and are not likely to be impacted by this trap. Climate change, which may allow farmers to till and plant earlier in the spring, could make matters worse. An earlier spring warm-up could also lead to a mismatch between nesting activities and food availability.
Professor Frances Buderman
“Last year’s stubble looks good to them from the air, but in reality, it does not offer the same advantages and protections that the grass does,” she said. “Over time, on a large scale, this association with cropland can lead to lower reproductive success and declining population numbers for early-nesting ducks that breed in the region.”
Buderman’s research group in the College of Agricultural Sciences previously focused on northern pintail ducks, a species that has been declining since the 1980s. They recognized northern pintails’ inclination to nest in agricultural fields as an “ecological trap” since the quantity of pintails the next year decreased as a result of demographic processes such as reproduction and survival as farmland use increased.
The researchers were left wondering, however, if the response of the northern pintail was unique, potentially explaining the different trends in abundance among waterfowl in the region.
In findings published on April 24 in the Journal of Animal Ecology, Buderman and colleagues report that the timing of nesting is a key factor in determining the effect of nesting in cropland on demographic processes. The most unfavorable demographic reactions to agricultural fields were observed in early nesting ducks.
“This isn’t to say that all early nesting waterfowl are going to struggle,” Buderman said. “Early-nesting ducks that don’t nest in cropland, and diving ducks such as canvasbacks, nest over water and are not likely to be impacted by this trap. Climate change, which may allow farmers to till and plant earlier in the spring, could make matters worse. An earlier spring warm-up could also lead to a mismatch between nesting activities and food availability.”
To reach their conclusions, the researchers analyzed data from the Waterfowl Breeding Population and Habitat Survey from 1958 to 2011 and focused on nine duck species that have traditionally used the Prairie Pothole Region as their breeding grounds: American wigeon, blue-winged teal, canvasback, gadwall, mallard, northern pintail, northern shoveler, redhead and ruddy duck.
The researchers calculated species-specific responses to temperature and land-use variables in the region, which has transitioned from mixed-grass prairie to cereal grain, oil crop fields, corn, wheat, sunflower, and soybean fields.
They began by estimating the effects of changes in temperature and land-use factors on habitat selection and population dynamics for the nine species, assessing species-specific responses to environmental change.
The researchers were able to discern trends in species-level responses and determine where species chose characteristics that were damaging to their population dynamics (such as northern pintail and cropland).
They found that northern pintail, American wigeon and blue-winged teal often had extreme responses to changes in habitat, although not always in the same way, Buderman pointed out.
“Each of the species we studied reacted a bit differently to changes in climate and land-use,” she said. “We observed species-level differences in the demographic and habitat-selection responses to climate and land-use change, which would complicate community-level habitat management. Our work highlights the importance of multi-species monitoring and community-level analysis, even among closely related species.”
