Cropping methods can mislead ducks

Some of the best waterfowl breeding wetlands in the world are found right in our backyard. During the last Ice Age, kilometre-high glaciers pressed down on much of North America.

When the ice melted, millions of shallow pools were left behind. These pothole wetlands became home to hundreds of species and millions of waterfowl.

Today, the prairie pothole region (PPR) extends through southern Alberta, Saskatchewan and Manitoba south through Montana, the Dakotas, Iowa and Minnesota. Many droughts have threatened the region with multi-year droughts in the 1930s, 1960s, 1980s and the early 2000s. But the region has prevailed, along with vast populations of dabbling ducks — except northern pintails.

According to Ducks Unlimited Canada, the 2018 Trends in Duck Breeding Populations report showed that, while numbers were down from 2017 due to a dry spring, total populations were high and healthy. An estimated 41.2 million breeding ducks were recorded, 17 percent above the long-term average. However, northern pintails were estimated at 2.4 million, an 18 percent decrease from 2017.

Recent research from Pennsylvania State University showed that pintails have become ensnared in an ecological trap that involves agricultural crop stubble, the ducks’ habit of not re-nesting, and their resistance to change even when the land around them changes.

“They are early spring nesters, so they are one of the first species to arrive in the PPR when prairie grasses and residual crop stubble look somewhat similar,” said Frances Buderman, assistant professor of quantitative wildlife ecology.

“They have a relatively low probability of re-nesting so, if their first nest is destroyed, they are less likely to nest again compared to some other species like mallards that are also early spring nesters but prolific re-nesters.

“In addition, fine-scale work on telemetered pintails (individual pintails monitored over a longer period of time) use cropland equal to their availability. (But) we found that pintails are actually selecting cropland, so if 50 percent of the landscape is cropland, more than 50 percent of pintails will nest there, resulting in a disproportionate loss of pintails if the habitat is not terribly good for successfully hatching nests.”

Based on previous research, her team has hypothesized that the increase in conservation tillage has also contributed to declines. Conservation tillage produces a landscape that looks inviting to a pintail. It might encourage them to build a nest but put them in harm’s way of mechanized seeding.

However, fallowing can work in their favour.

“We found that fallow fields were selected by pintails and resulted in a positive effect on the number of pintails the next year in contrast to tilled cropland, which had a negative effect the next year,” said Buderman.

“With growing interest in cover crops and some clear indications that there are real and measurable benefits to soil health and other needs of the individual landowner, that may well present an opportunity for increased pintail production.”

She added that fall-seeded varieties of cereal grains such as winter wheat are valuable to pintails. Research has shown that pintails nest successfully in fall-seeded crops because it is more difficult for predators to find their nests.

“These fields require little mechanical activity in the spring during pintail nesting,” she said. “Increasing perennial cover such as pasture and hay could offer significant opportunities in key pintail areas especially where there is demand from cow-calf operators for increasing herd size or forage.”

The research team used a program that allowed them to identify the influence of long-term changes in climate and agricultural land use on both the selection and quality of habitat for pintails.

Buderman said pintails are less likely to change their nesting behaviour in response to on-the-ground pond conditions. It is possible that, at some point in their evolutionary history, it was either beneficial for them to keep their nesting strategies regardless of conditions or they were not exposed to significant annual variation in nesting conditions. As a result, flexible breeding behaviour was apparently not an important trait for them to have.

“We are currently pursuing a multi-species version of this framework that will allow us to pinpoint which natural history characteristics are good predictors for the response of species to climate and landcover changes.”

Buderman said that shallow wetlands are more productive in terms of the small seeds and invertebrates that are the preferred diet of pintails. These wetlands are the first to thaw, warm up, and produce invertebrates vital to the duck’s needs to produce a clutch in early spring.

However, she said wetland drainage has reduced the number of ponds and the changed food availability in ponds.

“The climate has also generally become drier in the western PPR, but wetter in the eastern PPR, resulting in fewer wetlands in the west and more in the east. More wetlands as a product of increased precipitation aren’t necessarily good wetlands for pintail, because they may be larger and deeper than the wetlands pintails prefer.

“In addition, the remaining patches of grassland are smaller and more fragmented than they would have been previously.”

She said fragmented landscapes tend to increase predator efficiency.

The study was published in the Journal of Animal Ecology.

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