by Johann Walker and Scott Stephens Ph.D.
After a long migration northward from the Gulf Coast, a hen pintail has finally arrived on the prairies of North Dakota in late April. She and her mate have established a territory on a shallow wetland in the middle of several square miles of native grassland. She has spent many days feeding and carefully inspecting potential nest locations in the surrounding pasture. Now she is ready to nest. The hen pintail lands at her chosen site, scrapes out a shallow depression in the soil next to a clump of little bluestem grass, and lays her first egg. If she has chosen a good nest site and luck is with her, her eggs will hatch, and she will lead a brood of ducklings to a nearby wetland in three to four weeks.
Selecting a nest site is an important decision in the annual cycle of ducks. Nest site choice can influence whether the female survives the nesting season and her eggs survive to hatch. A poor choice might expose the nesting female and her eggs to predators, destruction by machinery, or flooding. This aspect of nesting behavior is shaped over time by natural selection, reflecting strategies that have been effective for the species.
Ducks generally use three strategies for nest site selection. Notwithstanding the occasional mallard that nests in a backyard apple tree, most ducks can be categorized as either upland nesters, overwater nesters, or cavity nesters. Upland nesters include the familiar puddle ducks like mallards and pintails as well as some divers like white-winged scoters and lesser scaup. Overwater nesters include many diving ducks including canvasbacks, ruddy ducks, redheads, greater scaup, and ring-necked ducks. Cavity nesters are wood ducks, buffleheads, goldeneyes, and mergansers (although the common and red-breasted mergansers will also nest on the ground). These nesting strategies are best understood in the context of each species' life history and habitat.
Pairs of upland-nesting ducks begin arriving in the Prairie Pothole Region just after ice out. They settle on shallow, seasonal wetlands, many of which are less than one acre in size and are embedded in cropland, pasture, hay meadows, and perennial grassland. The females feed heavily on protein-rich invertebrates in these shallow wetlands, and pairs of breeding ducks establish wetland territories that are defended by drakes to ensure their mates have sufficient food resources to recover from migration and begin nesting. Most mallards and pintails establish breeding territories on wetlands from mid-April to early May. Once the birds have established territories and acquired adequate nutrient reserves, upland-nesting ducks begin prospecting for potential nest sites. During this period, it's common to see pairs of ducks walking along the edge of nesting cover.
Where upland-nesting ducks ultimately nest varies among species. Blue-winged teal, which have a smaller home range than other species, build their nests close to wetlands. Bluewings are also willing to nest in rather sparse cover compared to many other species. In contrast, mallards have large home ranges, and hens sometimes nest more than a mile from their wetland territory. In addition, mallards typically nest in some of the thickest nesting cover available.
Overwater nesters make their nests on floating mats of emergent vegetation like cattails and bulrush. Their preferred nesting sites are semipermanent wetlands with relatively deep water and dense stands of emergent vegetation. Ideally, females select nest sites that provide cover and protection as well as an easy escape route if they have to flee the nest. Once a suitable overwater nest site is located, females create a platform of nesting material on which to safely deposit their eggs.
Redheads and canvasbacks, which largely breeding in the Prairie Pothole Region, typically establish breeding territories on relatively deep, semipermanent wetlands ringed by a thick wall of tall cattails. The bottom third of these six- to eight-foot plants is often underwater. Female redheads and canvasbacks make floating nest bowls by folding cattails down into a cup-shaped raft.