- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; the Black Tern was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
Global in distribution, in North America the Black Tern is broadly distributed across the northern United States and central Canada, ranging from British Columbia and eastern Oregon and Washington, east through the Great Lakes, southern Ontario, and southwestern Quebec. Scattered populations occur just to the south and east of this range. The core of the Black Tern’s breeding range occurs in the prairie potholes of the Dakotas and the Canadian Prairie Provinces (Figure 1).
Assigned a Continental Concern Score of 12/20 by Partners in Flight, and designated a species of Moderate Concern by the North American Waterbird Conservation Plan and a Common Bird in Steep Decline by the North American Bird Conservation Initiative. Designated a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources, and a Target Conservation Species by Audubon Minnesota.
A medium- to long-distance migrant that spends winters along the coasts of Central America and northern South America.
Feeds primarily on aquatic insects secured by dipping its bill to the water’s surface while in flight.
A shallow platform of aquatic vegetation built on a mat of floating vegetation or atop muskrat houses; occasionally found on floating debris, boards, mud patches, artificial nesting platforms, or nests abandoned by other marsh-nesting birds.
In the early 1900s, Roberts (1932) not only described the Black Tern as “an abundant summer resident, breeding throughout the state” but also wrote that “no other water-bird is more generally and abundantly distributed in Minnesota.” It could be found, he wrote, in suitable wetlands “in all parts of the state.” Knowing the rarity of the species’ marshy habitat in the far northeastern and north-central corners of Minnesota, one has to question Roberts’s broad assertion of its statewide abundance. Confirmed nesting records (nests with eggs) were available from only a handful of central and western counties and locations that Roberts and his colleagues visited most frequently: Hennepin (Minneapolis), Kittson, Morrison, and Sherburne Counties and Leech Lake. Birds constructing nests were observed in Marshall County.
Forty years later, Green and Janssen (1975) described the tern’s statewide distribution as including all but the extreme northeastern region of the state, with no confirmed nesting reports from Lake or Cook Counties. Janssen (1987) later noted the tern’s absence not only from Lake and Cook Counties but also from large portions of St. Louis and Koochiching Counties. He wrote that it was rare in southeastern Minnesota, in counties just west of the Mississippi River floodplain, and had declined in abundance throughout the river valley. Elsewhere in the state he delineated 30 counties where nesting had been confirmed since 1970. Hertzel and Janssen (1998) later added an additional 9 counties to the list.
Concern regarding the species’ status prompted the Minnesota Department of Natural Resources to conduct a statewide survey from 1990 through 1995. Observations were solicited in response to a “Black Tern Wanted” poster, which was widely distributed throughout the state. Observations were reported from 71 counties, and breeding was confirmed in 35 counties. Although there were reports from all but 1 northeastern county (Cook), nesting was confirmed only as far east as Itasca and Aitkin Counties (Baker and Hines 1996).
Similar results have been documented by field staff with the Minnesota Biological Survey. Since the late 1980s, they have identified 475 breeding season locations widely distributed across the state. Overall, the species was least abundant in southeastern Minnesota and was absent from the Arrowhead region, including Carlton and Pine Counties to the south (Minnesota Department of Natural Resources 2016).
During the MNBBA, participants reported 754 Black Tern records in 10.6% (503/4,751) of the surveyed atlas blocks and in 10.5% (245/2,337) of the priority blocks. Breeding evidence was confirmed in 88 (1.9%) of the surveyed blocks (Figures 2 and 3; Table 1). The species was observed in 72 of Minnesota’s 87 counties; breeding was confirmed in 38 counties. The latter included 15 counties not depicted in the county distribution map published by Hertzel and Janssen (1998): Carver, Clay, Cottonwood, Freeborn, Hubbard, Isanti, Kittson, McLeod, Meeker, Mille Lacs, Red Lake, Rice, Sibley, Stevens, and Wadena.
The landcover suitability model generated for the Black Tern using MNBBA data predicts that habitat is most suitable in the central regions of the state, from eastern Anoka County west to Big Stone County, and north to southern Beltrami and western Itasca County (Figure 4). Scattered pockets outside of this area are distributed throughout the state and include the extensive wetlands in eastern Marshall County and the Swan Lake wetland complex in Nicollet County.
Notwithstanding Roberts’s original assertion regarding the species’ statewide distribution, it appears that the overall distribution of the Black Tern has remained relatively unchanged over the past 100 years. The species is widely distributed across the state except in northeastern, north-central, and portions of southeastern Minnesota and the most intensively cultivated regions of the Red River valley. The same is true elsewhere in the tern’s breeding range. Although the southern edge of its distribution in North America has receded, the overall extent of the species’ distribution has changed very little since the late 1800s and early 1900s (Heath et al. 2009). Despite retaining the same overall distribution, other states and provinces in the region, including Michigan, Ontario, South Dakota, and Wisconsin, have documented significant population declines. In Michigan, 89 colony sites that were identified during the state’s first atlas (1983–1988) had been abandoned by the second atlas (2002–2008), and only 50 new colonies had been established, resulting in a net loss of 39 colonies (Chartier et al. 2013).
*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.