- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; also regular during the winter months in southern Minnesota. The Double-crested Cormorant was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
The Double-crested Cormorant can be found along both coastlines during the breeding season as well as at inland breeding sites in the central Canadian provinces and the north-central region of the United States, from Montana east through the Great Lakes. The core of its breeding population is centered in the northern Great Plains, including southern Minnesota (Figure 1).
Assigned a Continental Concern Score of 8/20 by Partners in Flight and considered a species not currently at risk by the North American Waterbird Conservation Plan.
Although some birds are seen year-round in Minnesota, most cormorants that breed in Minnesota are medium-distance migrants, wintering along the southern Atlantic Coast, the Gulf Coast, and on inland lakes and reservoirs in the southeastern United States.
Almost entirely small fish, obtained by diving and pursuing prey underwater. The species’ fish-based diet is the source of considerable friction among commercial fishermen and recreational anglers.
Uses a variety of materials to construct an open platform that may be placed on the ground, in trees or shrubs, or on mats of emergent wetland vegetation. A colonial nesting species.
Maligned for centuries, this large black bird easily captured the attention of the region’s Native Americans and early European explorers. Blackduck Lake, Crowduck Island, and Cormorant Point are just a few examples of Minnesota sites that clearly reference the species’ abundance hundreds of years ago. The 1821 Cass expedition noted cormorants on Lake Winnibigoshish, and in 1832 Henry Schoolcraft recorded the species’ presence on Leech Lake (Mortenson, pers. comm.). When Hatch wrote the first comprehensive account of Minnesota birds in 1892, he explained:
Except when the water is frozen firmly, there is no time in the year when they may not be seen in almost every general section where the conditions are favorable to their habits of feeding.
Migrant flocks passing through the state in the spring and fall were often of an enormous scale. Roberts (1932) included a spring 1918 report from former game and fish commissioner Carlos Avery, referring to complaints he was receiving of ten thousand or more cormorants in the bottomlands of the Minnesota River. Concerned about the species’ impact on the local fisheries, neighbors were asking the commissioner to take action. An excerpt from an April 1926 account of the species’ migration north along the Mississippi River, south of La Crosse, provides another example of the sheer magnitude of the numbers of Double-crested Cormorants during migration (Grassett 1926):
The flight was so large that at times it was impossible to see the sunset sky through the mass …The number of birds is variously estimated … from 100,000 to 1,000,000 birds.
Widely perceived as a “menace” to local fish populations, the Double-crested Cormorant was routinely molested and shot at in its nighttime roosts during migration and in its nesting colonies during the breeding season. Permits to shoot the species were issued by the Minnesota Game and Fish Commission, primarily during spring migration. Given the species’ quick demise, it is likely that many citizens simply took action into their own hands. Numbers had declined so precipitously by 1930 that Roberts’s account only documented three active nesting colonies in the state: Gull Rock in Lake of the Woods, Crane Island in Lake Minnetonka, and Kawishiwi Lake in Lake County. Together the three sites supported less than a few hundred birds. Several large, well-known nesting colonies had been abandoned, including three sites on lakes in southwestern Minnesota: Heron Lake (Jackson County), Loon Lake (Jackson County), and Lake Shetek (Murray County).
Despite the paucity of nesting birds, pillaging of the unprotected cormorant continued. In 1948, the editor of the statewide bird journal, then known as The Flicker (Warner 1948), wrote:
Information on the wholesale slaughter of this species on its rookeries and elsewhere in Minnesota during 1948 by organized groups and shooting parties has reached the editor’s desk. Is this killing justifiable? Or are these people misinformed as to the true relationships of this species to fish and the fishing industries? Or is this unprotected bird being shot largely in the name of “sport” at times when the game seasons are closed?
Warner ended his note with a call for more information about the species’ status. Observers throughout the state soon responded with reports of small colonies at widely scattered locations, including Rice Lake National Wildlife Refuge in Aitkin County (Hofslund 1950), Gull Rock in Lake of the Woods (Dobie 1956), and Shields Lake in Rice County (Hanlon 1956). Although the carnage continued and the species was not federally protected until 1972, populations in Minnesota and throughout North America were slowly rebounding.
Unfortunately, the new threat on the horizon in the 1950s was the widespread use of pesticides, which took its toll on many fish-eating species, including the Double-crested Cormorant. Contaminant levels were so high in the Great Lakes fish populations that they likely led to the cormorant’s extirpation on Lake Superior and Lake Michigan. But as contaminant levels gradually declined in the 1970s, this adaptable species once again bounced back. Populations not only stabilized, they began a slow and steady growth in numbers in the 1980s and early 1990s, followed by a period of rapid growth beginning in the late 1990s (Dorr et al. 2014; Sauer et al. 2017).
Just as populations were beginning to recover, the Minnesota Department of Natural Resources’ newly established Nongame Wildlife Program began to examine the status of all colonial waterbirds in the state. The program solicited reports from field staff working across the state and from other resource agencies, colleges, universities, and published accounts. Based on this information, program staff issued a series of five reports that tracked the distribution and abundance of all colonial-nesting species from the mid-1970s through 1985 (Henderson 1977, 1978, 1984; Henderson and Hirsch 1980; Guertin and Pfannmuller 1985).
These reports depicted the rapidly changing status of the Double-crested Cormorant. In 1977, 12 active colonies were identified in 8 counties: most colonies were located in central Minnesota and in the northwestern corner of the state. Just eight years later, 26 colonies were identified in 18 counties, including 7 colonies in Lake of the Woods. One of the latter sites, appropriately known as Crowduck Island, supported the state’s largest nesting colony, numbering 1,024 breeding pairs (Guertin and Pfannmuller 1985). During this period, both Green and Janssen (1975) and Janssen (1987) described the species as a statewide resident, common in all but the northeastern and north-central regions.
By 1998, Hertzel and Janssen would delineate confirmed nesting records in 28 Minnesota counties since 1970. When a statewide census was conducted in 2015, the Double-crested Cormorant was documented nesting at 36 sites distributed across 20 counties, stretching from Faribault County in south-central Minnesota north to Lake of the Woods, Itasca, St. Louis, and Lake Counties (Hamilton and Cuthbert 2016).
During the MNBBA, participants reported 1,165 Double-crested Cormorant breeding records from 12.7% (606/4,762) of the surveyed atlas blocks and from 13.5% (316/2,337) of the priority blocks. Breeding evidence was gathered in 57 atlas blocks (Figures 2 and 3; Table 1). The species was observed in 77 of Minnesota’s 87 counties and was confirmed breeding in 30 counties; the atlas block for the nesting colony located on Pig’s Eye Lake straddled 3 counties (Ramsey, Dakota, and Washington).
MNBBA surveyors originally reported over 400 “possible” breeding records and a handful of “probable” records for the Double-crested Cormorant. In the course of reviewing all MNBBA data, these records were changed to “observed.” Although the Double-crested Cormorant frequently feeds near its nesting colony (less than 10 km), some birds may travel up to 62 km to good foraging sites (Dorr et al. 2014). As a result, unless the birds are on or near the nest, observations away from the nesting colony cannot be assumed to indicate possible or probable breeding status where they are observed.
What Minnesotans have learned in the past 100 years, humanity has known for millennia: the Double-crested Cormorant is an extraordinary and very adaptable species (Wires 2014). The species has made a remarkable recovery from near decimation in the early 1900s, not only in Minnesota but throughout the Great Lakes and North America (Sauer et al. 2017). Given some of the reports of its abundance in the early 1900s, particularly during migration, it certainly has not recovered to its former level of abundance. In the face of increased calls for controlling local populations in the past decade, the challenge for wildlife managers is to sustain healthy populations while still addressing conflicts between burgeoning cormorant populations and concerns by local citizens about the species’ impact on local fisheries.
*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.