Lesser Scaup

A regular yet rare breeding resident and migrant; occasionally reported during the winter months where there is open water, particularly along the Lower Mississippi River. The Lesser Scaup was a rare species during the Minnesota Breeding Bird Atlas (MNBBA).

A northern boreal species, the Lesser Scaup’s breeding range extends from Alaska across Canada and south into the northwestern and north-central states. The boreal forest regions of western Canada are believed to support the highest densities of breeding birds, followed by the Prairie Pothole Region. Its distribution and relative abundance in southern Canada and the United States, as depicted by the federal Breeding Bird Survey (BBS), are shown in Figure 1.

A game species, the Lesser Scaup has been assigned a High Continental Priority by the North American Waterfowl Management Plan, and assigned a Continental Concern Score of 11/20 by Partners in Flight; designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.

A short- to medium-distance migrant that winters throughout the southern United States and Pacific coast, the Caribbean islands, and Central America. The vast majority of birds, however, winter along the Gulf coast of the United States.

Omnivorous diver feeding on aquatic invertebrates and plants.

A shallow bowl on the ground or in a mound of aquatic vegetation over water.

Roberts’s (1932) account of the species in the early 1900s focuses almost entirely on the Lesser Scaup’s status as a common spring and fall migrant, particularly in western Minnesota. His comments regarding the species’ breeding status were limited. After describing detailed accounts of the species’ abundance during the fall flight that were submitted by observers throughout the state, he went on to question whether Lesser Scaup could ever have ever been very abundant during the breeding season and been missed by so many observant individuals:

From such reliable records as exist it seems improbable that the Scaup ever nested in considerable numbers anywhere in Minnesota, except, perhaps, in the northwest corner, where so many other Ducks spent the summer. There are no recent reports of nests or young, though pairs may be seen in the breeding-season throughout the state, suggesting nesting, but such occurrences cannot be taken as conclusive evidence.

Although he reported on records he received of pairs and multiple birds from several widely scattered western counties, confirmed nesting records (nest with eggs or flightless young) were limited to Marshall County (1891), Meeker County (1903), Otter Tail County (1893), and Itasca State Park (1919). In addition to these records, there was a report in June 1901 at Mud Lake in Marshall County that Lesser Scaup were one of the common ducks observed and “evidently breeding,” although no young or nests were seen. Many years later, when Breckenridge surveyed western Minnesota in the summer of 1929, he found only scattered pairs of birds and some lone males, from Lincoln County north to Kittson County. The largest number of birds was just 3 to 4 pairs at Twin Lakes in Kittson County (Roberts 1932). With the scarcity of records and accounts, it is a bit surprising that Roberts made the statement that the Lesser Scaup was “formerly a more common summer resident, now much reduced in numbers in the nesting season.” Little detail to support that premise is provided in his account.

In 1975, Green and Janssen reported the species was the rarest breeding duck in the state and limited to the northwest counties. The only confirmed nesting report (e.g. nest with eggs or flightless young) since Roberts wrote his account was in 1942 in Kandiyohi County. Records maintained by the Minnesota Ornithologists’ Union also include reports of several broods seen during the summer of 1963 in Clearwater County (1 pair with 7 young) and Mahnomen County (several pair with young) (Minnesota Ornithologists’ Union 2016). Reports of nonbreeding individuals elsewhere in the state were not uncommon. Nevertheless, when Janssen (1987) and Hertzel and Janssen (1998) published their maps of counties where nesting had been confirmed since 1970, Marshall County was the only county where breeding had been documented.

The species’ status as a rare breeder has changed little over the years. To date, the Minnesota Biological Survey has reported only 13 breeding season locations in 6 counties: Clearwater, Kittson, Marshall, Pennington, Pope, and St. Louis (Minnesota Department of Natural Resources 2016).

During the MNBBA, participants reported just 49 records of Lesser Scaup in 1.0% (46/4,734) of the surveyed atlas blocks and in 1.2% (29/2,337) of the priority atlas blocks. Confirmed breeding evidence was not found in any block (Figures 2 and 3; Table 1). In total, the birds were observed in 30 of Minnesota’s 87 counties. Although the majority of records were from the western half of the state, there were also scattered records in north-central, northeastern, and southeastern counties. Such reports may represent young, nonbreeding individuals, as Lesser Scaup may not breed their first year. Because the population has a skewed sex ratio in favor of males, not all males can find females. Various reports place the ratio anywhere from 57% males to as high as 87%. In addition, females may delay breeding until their second or third year, especially if wetland conditions are poor (Baldassarre 2014).

The increasingly wide dispersion of observations during the summer months appears to be a long-term trend in Minnesota. An examination of all the summer reports submitted to the Minnesota Ornithologists’ Union since the 1960s shows a steady and marked increase in the number of counties where the birds are reported each summer, particularly in the past five years (Figure 4). These birds may be young dispersers from increasing breeding populations recently documented in the Dakotas (Anteau et al. 2014).

In their review of the species, Anteau and his colleagues (2014) commented that “there is no compelling evidence of historical changes in the range of Lesser Scaup. However, there is new evidence that the breeding range is larger than was previously thought (Schummer et al. 2013).” They specifically point out that areas along the southern periphery of its breeding range, where the species is thought to have decreased in abundance, are now being reoccupied, including in North and South Dakota. The species may also have expanded eastward in Ontario and Quebec since the middle of the 20th century (Anteau et al. 2014).

*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.

Typical breeding habitat, particularly in the Great Plains, consists of seasonal, semipermanent, and permanent wetlands with stands of emergent vegetation, including sedges, bulrushes, and cattails (Figure 5). Such wetlands are embedded in a landscape surrounded by native prairie, restored grasslands, and hayfields. In neighboring North Dakota, Lesser Scaup used seasonal wetlands to a greater extent than any other diving duck in the region (Kantrud and Stewart 1977). To the north, in Manitoba, studies show the birds usually select small wetland basins, averaging less than 0.8 ha in size (Hammell 1973). As the young become older, the female moves the broods from the smaller, seasonal wetlands to larger, more permanent wetlands (Sugden 1973).

Scaup are included in the annual Waterfowl Breeding and Habitat Survey that is conducted by the U.S. Fish and Wildlife Service and the Canadian Wildlife Service. But given the difficulty of distinguishing Greater Scaup and Lesser Scaup, especially from the air, the counts are simply reported as a combined estimate for both species. In 2015, the total estimated population of scaup was 4.4 million birds in the Traditional Survey Area, which covers central and western Canada and the U.S. northern Great Plains, where the core of the Lesser Scaup population occurs (Zimpfer et al. 2015). This number is well below the continental population objective established by the North American Waterfowl Management Plan in 2004 of 6.3 million birds (North American Waterfowl Management Plan 2004). Overall the population declined from the 1980s through 2005 but has increased and stabilized in subsequent years (Figure 6).

The decline in numbers was most prevalent in the northern boreal forests of Alaska, the Yukon, and the Northwest Territories, a region where Lesser Scaup are more abundant than Greater Scaup. In addition, biologists have estimated that nearly 90% of the continental scaup population is comprised of Lesser Scaup (Bellrose 1980), further pointing to its decline. Although populations in the U.S. Great Plains have increased, they contribute such a small percentage to the continental population that the increase is insufficient to offset the larger-scale, more widespread decline in Canada (Anteau et al. 2014). The BBS also shows a significant population decline survey-wide from 1966 to 2015 of 1.84% per year, with the largest, statistically significant declines in the Boreal Taiga Plains of the Northwest Territories and northern Alberta. Similar to the data from the Waterfowl Breeding and Habitat Survey, BBS data also suggest an increase from 2005 to 2015 (Sauer et al. 2017).

In Minnesota, the annual waterfowl survey conducted each May shows a significant downward trend in scaup numbers (Figure 7). Unfortunately the survey does not cover the Lesser Scaup’s primary breeding range in the state, northwestern Minnesota. In addition, because scaup are late migrants, many birds are still passing through northern Minnesota in May. As a result, the survey may more accurately depict the status of migrant scaup. Figure 7 also depicts a contrasting scenario to the data presented in Figure 4, which documents more summer seasonal observations of Lesser Scaup in Minnesota. At least one analysis has demonstrated that the range-wide decline in the Lesser Scaup’s abundance has been driven by significant declines in northwestern Canada. In the United States, significant long-term increases have been documented in regions of North and South Dakota (Anteau et al. 2014). The increase in summer reports in Minnesota may be a consequence of the species’ increasing abundance farther west.

A rare breeding species in Minnesota, the Lesser Scaup is actually one of the most abundant and widely dispersed waterfowl species in North America. Nevertheless, like many boreal waterfowl species, it has not been well studied. This has made it challenging to understand the species rather dramatic population decline since 1978. Most waterfowl species experienced declines in the 1980s and 1990s due to drought conditions, but nearly all have since recovered. The continued decline of the Lesser Scaup represents, as Baldassarre (2014) notes, “a biological conundrum.” Intensive field studies are now underway to unravel the mystery. Among the theories postulated are (1) habitat loss due to increased agricultural development as well as expanded oil, mineral, and gas extraction; (2) increased timber harvesting; (3) climate change; (4) reduced food on important migratory stopovers; and (5) increased contaminants (Baldassarre 2014). Indeed, relative to food availability, an important study conducted in Minnesota documented that there were 94% fewer amphipods, an important food item for Lesser Scaup, in wetlands that were sampled in 2000–2001 than in the same wetlands almost 20 years earlier (Anteau and Afton 2006).

Given the Lesser Scaup’s decline, the North American Waterfowl Management Plan (2004) designated it a species of High Continental Priority in 2004. The U.S. Fish and Wildlife Service designated it a focal species in 2012 (U.S. Fish and Wildlife Service 2011), and in Minnesota it is a Species in Greatest Conservation Need (Minnesota Department of Natural Resources 2015). Partners in Flight (2017) assigned it a moderate Continental Concern Score of 11/20.

A harvested species, Lesser Scaup comprised approximately 2.1% (226,304 birds) of the total duck harvest in the United States in 2015. The 2015 fall harvest of Lesser Scaup in Minnesota comprised less than 6% (13,046 birds) of the total harvest in the United States, and only 2.3% of the total number of ducks harvested in Minnesota (Raftovich et al. 2016). Historically, scaup were extremely important in Minnesota’s duck harvest, and they were often one of the top three species harvested through the 1960s. Their importance has declined, especially in the past 10 years.

Numerous studies have examined the potential impact of a variety of contaminants on scaup populations, including organochlorines, mercury, lead, and selenium. The majority of studies, however, have demonstrated little if any population level impacts. Recent work in Minnesota is examining the factors responsible for large die-offs of thousands of migrant scaup from ingesting nonnative faucet snails, a host for several intestinal trematodes (Roy 2013).

The overall impact of these potential threats to Lesser Scaup populations is considered small compared to the large-scale loss and degradation of habitat. Even though it is a rare breeding species in Minnesota’s western grasslands, Lesser Scaup should benefit from continued actions to protect and restore the state’s wetlands and grasslands, which are spearheaded by the Minnesota Duck Recovery Program (Minnesota Department of Natural Resources 2006) and the Minnesota Prairie Landscape Conservation Initiative (Minnesota Prairie Plan Working Group 2011). These efforts will benefit both local populations and migratory populations.

Ultimately, the Lesser Scaup’s survival is tied to the protection of critical breeding habitat in Canada, where more than 65% of the population resides. Further development of these northern regions is a primary threat, as habitat is lost to logging, agriculture, and a rapid expansion in the oil and gas industry. A warming climate may further exacerbate the challenges. A recent study conducted by the National Audubon Society examined the impacts of a warming climate on nearly 600 North American birds, including the Lesser Scaup. Their results predicted a 65% loss of the species’ current breeding habitat by the year 2080, forcing the birds to move farther north into the Arctic regions now occupied by the Greater Scaup (Langham et al. 2015; National Audubon Society 2016). In lieu of the results, the species was classified as “climate threatened”.