By Jim Devries, Ph.D.
As you read this, hen northern pintails are well into the trials and tribulations of their annual breeding effort. What happens during these few short months, including the number of ducklings that hatch and fledge and the number of females that survive, greatly influences whether the pintail population grows or declines. Where pintails choose to nest across their vast breeding range has a significant impact on their productivity and, consequently, on how many birds migrate south in the fall.
For some duck species, the choice of where to nest is relatively simple; they return to the place where they nested the previous year. Canvasbacks serve as a good example of this strategy, known as philopatry. But pintails are different in this regard. More than other species, pintails follow a "nomadic" strategy in which they seek out breeding locations that have experienced good winter precipitation and have favorable spring wetland conditions.
The Prairie Pothole Region (PPR) is usually the first choice for many breeding pintails, as long as runoff from a good winter snowpack has filled numerous pothole wetlands on the landscape. In drier years, many pintails "overfly" the prairies and settle in the Boreal Forest of Alaska and northern Canada or continue even farther north to the Arctic lowland tundra, where wetland conditions are generally more stable than on the prairies. However, this decision seems to come at a cost. Fewer young are produced in years when large numbers of pintails settle in northern breeding areas. As a result, the prairies are where the fate of the pintail population is largely determined each year.
Changing Agricultural Practices and Habitat Loss
As most waterfowlers are aware, the pintail has seen hard times in recent years. Unlike many duck species whose populations have expanded to record levels lately, pintail numbers have remained stubbornly low. Annual pintail breeding populations, which averaged slightly fewer than 6 million birds during the 1970s, have fallen to about 3 million birds in recent years. This decline has occurred primarily in the Canadian PPR, while counts on the U.S. prairies have remained relatively stable.
What has caused the precipitous drop in pintail numbers on the Canadian prairies? Population declines of this magnitude are generally the result of changes in either reproductive success or survival. For pintails and other ducks, reproductive success hinges on the ability of females to successfully produce and hatch a clutch of eggs and to raise their ducklings to fledging. Survival depends on the birds' ability to avoid predation and other forms of natural mortality during all parts of the annual cycle, as well as harvest by hunters. Analysis of band returns over recent decades shows little evidence of changes in annual survival rates among pintails. As a result, our attention has focused on factors that may have reduced pintail breeding success. To understand what may be going on, we need to understand the breeding ecology of pintails.
Pintail hens are different from other prairie-nesting ducks because they are much less selective about where they make their nests. Most female ducks choose nest sites in places that are well concealed from potential predators, but pintails pursue a more flexible strategy. Several recent research studies have shown that pintails will generally select nest sites with little regard for the type of surrounding vegetation or land use. Thus, the chance of finding a pintail nest fully exposed in cropland is almost as great as finding one well concealed in thick grass. In fact, recent research conducted by Ducks Unlimited Canada (DUC) scientists estimated that on average, about 40 percent of all pintail nests on the prairies may be initiated in cropland. And this could be a problem.
Most pintails start nesting in late April and early May, and it takes about 32 days for the birds to lay and incubate their eggs. As a result, many pintail nests located in cropland are likely to be destroyed by spring cultivation and seeding operations that typically occur during May and early June. Almost 100 years ago, ornithologist Walter Goelitz wrote an article titled "The Destruction of Nests by Farming Operations in Saskatchewan." In that piece, which appeared n a 1918 issue of the journal The Auk, he reported that "pintails were in the lead" in the numbers of nests found in cultivated fields near Regina, Saskatchewan.
We don't have pintail population estimates from that long ago, but we do know that the amount of cropland on the prairies has vastly increased. Crop census data indicates that since 1921, cropland area in the Canadian PPR has more than doubled, from about 32 million to 72 million acres, largely at the expense of native grasslands. However, since most of that increase occurred prior to the 1970s, grassland loss alone doesn't appear to be an adequate explanation for the more recent pintail decline. In fact, the conversion of cropland back to pasture and other forms of grassland-based agriculture has been increasing in recent years.
Perhaps a more likely explanation for the pintail decline can be found in the way existing croplands are managed, which has changed dramatically in recent decades. During the 1970s, approximately 30 to 40 percent of croplands in the Canadian PPR were left unseeded every year through a soil-moisture conservation practice called "summer fallow." These fields were typically left undisturbed until mid- to late June before being cultivated for weed control. Thus, pintail nests initiated within these fields may have had a greater chance of hatching. Since the 1970s, cropland rested as summer fallow has declined from 27 million acres to 8.5 million acres as continuous cropping has become the standard practice on the prairies. The result is that croplands have become much more dangerous places for pintail nests. This may, in part, have reduced the capacity of the Canadian PPR to produce pintails, and therefore may explain some of the species' recent declines.
Another ongoing threat to pintails and other breeding waterfowl in Canada is wetland drainage. In the United States, prairie potholes were federally protected under the Clean Water Act until 2001 and each Farm Bill since 1985 has included economic disincentives for wetland drainage. However, no such protections have been in place in Canada. Environment Canada estimates that approximately 9 percent of the wetland area in the Canadian PPR was lost to agricultural drainage from 1985 to 2010. Moreover, much of this lost habitat consisted of temporary and seasonal wetland basins, which are especially important to breeding pintails.
Challenges on Migration and Wintering Areas
While habitat loss and changing agricultural practices on the breeding grounds have likely played a large role in the decline of pintail populations, ongoing changes to wintering and migration habitats may now be equally important. Not surprisingly, the availability of food in winter and during migration has the potential to affect the fortunes of waterfowl. Vital nutrients acquired while feeding in wetlands and on agricultural lands not only bolster overwinter survival, but also prepare the birds for the spring migration and the energetic demands of breeding. Females in poor condition may be delayed during migration, initiate nests later, invest less effort in nesting, or forgo breeding altogether.
During the winter months, pintails congregate in several regions where crucial habitats are under threat. The continent's most important pintail wintering areas are the Central Valley of California; the rice-growing regions of Texas, Arkansas, and Louisiana; the Gulf Coast marshes of Texas and Louisiana; and both mainland coasts of Mexico. Ironically, while croplands on the breeding grounds present a challenge for nesting pintails, agricultural lands associated with wetlands on the wintering grounds have become vitally important habitat for the birds. In many areas, managed wetlands and agricultural lands have largely replaced natural wetlands in supporting wintering pintails and many other wetland birds.
Rice, an especially energy-rich grain, has become a primary food source for wintering pintails and other ducks. Across the United States, more than 700,000 acres of harvested rice fields are flooded during the winter months. These fields are rich not only in waste rice but also in weed seeds and aquatic invertebrates eaten by wintering ducks. In the Central Valley of California, where 35 percent of North America's pintails winter, between 150,000 and 350,000 acres of rice fields are flooded annually. A large percentage of the diet of pintails wintering there is composed of waste rice. Flooded rice fields are especially important to waterfowl in the Central Valley, given that almost 95 percent of its historical wetlands have been lost since settlement. On the Gulf coastal plain of Louisiana and Texas, which annually hosts about 25 percent of the continent's wintering pintails, approximately 150,000 acres of rice fields provide crucial foraging habitat for waterfowl. Studies have shown that these agricultural habitats offer pintails significantly more food energy per acre than nearby coastal saline marshes.
Unfortunately, the availability of flooded rice fields is declining in many areas. Widespread drought, rising production costs, changing agricultural practices, and competing water demands have led to declining rice acreage and reductions in winter flooding as a rice straw management practice. In the Gulf Coast region of Texas and Louisiana, rice acreage has declined by more than 50 percent since the early 1970s, falling victim to the economics of competing crops and, more recently, water shortages. And while California's rice acreage has remained relatively stable, this crop is particularly sensitive to the vagaries of water availability. Record-breaking drought in California resulted in an 80 percent decline in flooded rice acreage during the winter of 2014-2015, and much-needed rains this past winter provided only marginal increases in flooded rice acres. The disconcerting reality is that wintering pintails are now highly reliant on the planting and management of this water-dependent agricultural crop.
Pintail populations are also facing emerging threats on key migratory "staging" areas. These relatively small areas play a disproportionately large role as refueling stops for pintails and many other waterfowl species on their northward migrations. Ducks and geese rely on food resources available on staging areas to acquire the energy and protein needed to complete their spring migration and to prepare females for egg production. For pintails, two of the most important staging areas include the playa lakes region, which stretches from the Texas Panhandle to the Rainwater Basin of southern Nebraska, and the Southern Oregonâˆ’Northeastern California (SONEC) region in the intermountain west.
Roughly 8 million to 10 million waterfowl-including 30 percent of the continental pintail population-stop to rest and refuel in the Rainwater Basin during the spring migration. While the region has lost 97 percent of its historical wetlands-only about 400 of an estimated 11,400 basins remain-waste grain in agricultural fields and moist-soil plant seeds and invertebrates in remaining natural wetlands still provide crucial food resources for the migrating flocks.
Challenges facing pintails and other waterfowl in the Rainwater Basin include competition for limited irrigation water supplies, increasing demand for cropland, and disease outbreaks on overcrowded wetlands.
While the importance of the Rainwater Basin has been known for more than a century, the SONEC region was only recently discovered to be a vital spring staging area for pintails and other Pacific Flyway waterfowl. By tracking pintails carrying satellite transmitters during their northward migration, researchers have estimated that 85 percent of the pintails that winter in the Central Valley funnel through this region on their way to the prairies and northern breeding areas. The primary habitats used by staging pintails in the SONEC region are flood-irrigated pastures and hay fields. The diversion of natural spring runoff for flood-irrigation is a longstanding agricultural practice here and occurs mostly on altered seasonal wetlands that were historically dependent on natural flooding from snowmelt. These habitats are visited by pintails both day and night, indicating that the birds use them for resting and feeding. Recent food habit studies show that natural seeds produced by wetland plants and upland grasses in flood-irrigated pastures and hay fields make up the bulk of the pintail's diet in this area. Unfortunately, changes in agricultural practices are altering the suitability of many SONEC landscapes for pintails as the cost of maintaining aging flood- irrigation infrastructure has resulted in a move to less management-intensive center-pivot irrigation systems.
Restoring Pintail Populations and Their Habitats
While pintails and their habitats face serious threats on their breeding, migration, and wintering areas, there is cause for optimism about the future of these magnificent birds. Over the past few years, pintail populations have increased, albeit slightly. Progress is also being made in conserving crucial pintail habitats through the work of Ducks Unlimited's affiliates in the United States, Canada, and Mexico as well as a host of state, provincial, federal, and private conservation partners under the banner of the North American Waterfowl Management Plan.
On the breeding grounds, DU has made great strides in increasing the acreage of winter wheat planted in the Canadian PPR. Unlike spring-seeded crops, winter wheat is planted in the fall and remains undisturbed throughout the spring nesting period, giving nesting pintails a much better chance of hatching broods. In addition, DU continues to make progress in protecting and restoring prairie grasslands and wetlands across the PPR through direct acquisition and conservation easements.
On the wintering grounds, DU is working closely with the USA Rice Federation, rice producers, and federal policymakers to ensure that a strong U.S. rice industry is sustained, including management practices that provide vital habitat for pintails and other waterfowl. And DU is working hard across all waterfowl wintering areas to perpetually protect, restore, and manage wetlands that provide crucial feeding and resting habitat for ducks and geese.
Finally, DU is focused on maintaining and increasing wetlands on vitally important migratory staging areas visited by pintails and other waterfowl. From Texas north to the Rainwater Basin, these efforts have been bolstered by the recognition that remaining playa wetlands play a crucial role in recharging the underlying Ogallala aquifer, a vital water source for both people and agriculture. And in the SONEC region, DU and its partners are assisting landowners in maintaining and managing flood-irrigated pastures and hay fields to ensure that these "working wetlands" continue to support pintails and other waterfowl during their northward migration.
Across all regions and during all seasons, it's clear that the fate of pintails rests in our hands. The ability of these birds to reproduce and survive has become inextricably linked to our actions on the land. As you read this, many pintail nests across the breeding grounds have already begun to hatch. With favorable weather, an attentive hen, and a bit of luck, the downy pintail ducklings will find their way to nearby wetlands, thrive, and grow strong for the coming fall migration.
Dr. Jim Devries is a research scientist based at DU Canada's national headquarters in Stonewall, Manitoba.