- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; late migrants and overwintering birds are uncommon but regular in the winter months, especially in southern Minnesota. The Great Blue Heron was a common species during the Minnesota Breeding Bird Atlas (MNBBA).
Widely distributed across southern Canada and the United States, extending south into portions of Mexico; the Great Blue Heron reaches some of its highest breeding densities in eastern North America, especially from the Great Lakes states south to the Gulf coast (Figure 1).
Assigned a Continental Concern Score of 8/20 by Partners in Flight and designated a species Not Currently at Risk by the North American Waterbird Conservation Plan.
A partial migrant; some populations are nonmigratory, but most northern birds move south, some as far as Central America and northern South America, during the winter months.
Small fish, aquatic invertebrates, amphibians, reptiles, small mammals, and birds.
A platform nest built of sticks and usually placed in a tree, often 6 to 18 m above the ground. A colonial nesting species.
This majestic bird can be seen throughout the state during the summer season. Nesting colonies may range in number from just a few pairs, which can be difficult to locate, to large, mixed-species colonies that contain hundreds of nesting pairs. Often these are well known to local citizens and biologists alike.
When Roberts wrote his account of the species in 1932, there were records of 16 to 18 large Great Blue heronries in the files of the Bell Museum of Natural History. The majority of the colonies were located within the Eastern Broadleaf Forest and Laurentian Mixed Forest Provinces. They included heronries at several well-known nesting sites, such as Swan Lake in Nicollet County and Shields Lake in Rice County. Nesting records for the Shields Lake colony dated back to at least 1889 (Hanlon 1956). In addition to these large, well-known colonies, there were occasional reports of one or a few pairs nesting in trees along the edges of wetlands and lakes in western Minnesota, including the huge wetland complex at Heron Lake in Jackson County. At the time, however, breeding colonies (i.e., colonies in various stages of the nesting cycle) were documented in only 7 counties: Benton, Crow Wing, Hennepin, Murray, Nicollet, Polk, and Rice.
Because of its proximity to the Twin Cities, one of the best-known colonies was one located on Crane Island in Lake Minnetonka. A mixed colony of Great Blue Herons and Double-crested Cormorants, the colony had been active on the island since at least 1876. But in 1907 the construction of several homes prompted the birds to move to a larger, nearby island that was undeveloped. Unfortunately their eventual abandonment of the site was inevitable, as the lake’s rising popularity led to a dramatic increase in shoreline development and recreational activity, including the construction of a Boy Scout camp where the birds were nesting (Roberts 1932).
During the next 30 years, there were a few large colonies that were consistently visited and reported on by field biologists, bird clubs, and bird enthusiasts. These included a colony on the Rice Lake Refuge in Aitkin County (Bronoel 1951, 1958; Hofslund 1950, 1952), the Lake Koronis and Cold Spring colonies in Stearns County (Galati 1952, 1954, 1955; Partch 1990), and the Shields Lake colony in Rice County (Hanlon 1956; Rysgaard 1962). Three of the colonies were dominated by Great Blue Herons but also supported small numbers of Great Egrets and Double-crested Cormorants.
When Green and Janssen published their updated account of the species in 1975, they reported that the heron was a breeding resident throughout the state. At the time, however, no nesting colonies were known from the southwestern counties, and the few located in the northwest were small in size. A few years later, Janssen (1987) reported that nesting had been confirmed in 53 of Minnesota’s 87 counties since 1970. All the counties were north and east of the southwestern corner of the state. He also noted that colony size decreased as one moved north toward the state’s more densely forested landscape.
Several more comprehensive assessments of the species’ distribution and abundance began in the 1970s. First, both the Chippewa and Superior National Forests conducted forest-wide surveys of colonial waterbirds. Given that many of the colonies on these forests were small and in areas that were not very accessible, their work was a welcomed addition to knowledge of the species’ occurrence in these extensively forested landscapes. In 1976, 12 Great Blue Heron colonies were reported on the Chippewa National Forest (Mathisen and Richards 1978), and in 1979 and 1980, 15 and 14 colonies, respectively, were reported on the Superior National Forest (Siderits 1979, 1980).
At the same time, the Minnesota Department of Natural Resources’ Nongame Wildlife Program issued a series of reports in an effort to assemble a comprehensive inventory of all colonial waterbird nesting sites in the state (Henderson 1977, 1978, 1984; Henderson and Hirsch 1980). The reports were not based on a systematic, statewide inventory but were a compilation of reports from field staff as well as information compiled from other resource agencies, colleges, universities, and published accounts. The results were a good representation of the distribution of many species, particularly herons and egrets.
Using the data compiled by program staff, Guertin and Pfannmuller (1985) summarized the status of colonies that were active from 1981 to 1983. A total of 127 active Great Blue Heron colonies were reported, distributed across 46 counties. Thirty of the colonies occurred in the Arrowhead region of Cook, Lake, and St. Louis Counties; 78 of the colonies occurred in the northern forest region from Pine County west to Morrison County and north to Clearwater and Lake of the Woods Counties. Despite the large number of colonies in this region, the largest colonies, supporting the greatest number of nesting pairs, occurred farther south in the Eastern Broadleaf Forest and Prairie Parkland Provinces. Twenty-five of the 127 colonies were mixed-species colonies comprised primarily of Great Blue Herons, Double-crested Cormorants, Great Egrets, and Black-crowned Night-Herons. The majority of active colonies (75) supported from 1 to 50 Great Blue Heron nests, 2 colonies supported 500 to 1,000 nests, and only 1 colony numbered more than 1,000 nesting pairs. The latter was located on Long Lake in Kandiyohi County; in 1981 it supported 1,186 Great Blue Heron nests.
Nearly 15 years later, Hertzel and Janssen (1998) compiled confirmed nesting reports for 244 species known to have nested in the state since 1970. The Great Blue Heron was confirmed nesting in 54 counties. The fewest reports were from southwestern Minnesota and the Red River valley.
During the MNBBA, participants tallied 2,385 Great Blue Heron records in 34.1% (1,625/4,766) of the atlas blocks that were surveyed and in 39.4% (920/2,337) of the priority blocks. Breeding evidence was confirmed in 90 (1.9%) of the atlas blocks; 2 of these blocks, however, represent just 1 breeding locality (Egret Island on Pelican Lake in Grant County) (Figures 2 and 3; Table 1). The birds were reported in all 87 Minnesota counties and were confirmed breeding in 47 counties (1 block straddled Pennington and Marshall Counties). The list of breeding counties included 10 that were new to the list Hertzel and Janssen published in 1998: Benton, Blue Earth, Dodge, Jackson, Lyon, Mower, Pennington, Polk, Renville, and Steele.
Although surveyors originally reported far more probable and possible records than reported here, the vast majority of those records were changed to observed unless there was documentation that supported other breeding evidence codes. Great Blue Herons can travel far from the breeding colony to their primary foraging territories. Collectively, several studies have reported the mean distance traveled is from 2.3 to 6.5 km; others have reported that the birds range within 30 km of the colony, although most birds remain within 3 km (Vennesland and Butler 2011; Custer and Galli 2002). As a result, unless birds are seen on the nest, other observations cannot reasonably be assumed to indicate possible or probable breeding status.
Conducted approximately 30 years after the compilation prepared by Guertin and Pfannmuller in 1985, the MNBBA provides a reasonable data set to compare with the earlier data. MNBBA data suggest that the heron’s statewide distribution has changed very little. The number of nesting colonies, however, appears to have declined from the 127 reported in 1985 to the 90 confirmed MNBBA nesting reports. Data from the federal Breeding Bird Survey (BBS) also demonstrate a declining state population.
Little has been written about broad-scale changes in the distribution of Great Blue Herons in the past 100 years beyond changes in abundance at individual colonies. Nearby states and provinces that have conducted two breeding bird atlases, such as Ohio (Rodewald et al. 2016), Michigan (Chartier et al. 2013), and Ontario (Cadman et al. 2007), have noted little change in distribution but a decline in overall numbers in Ontario and Michigan and an increase in Ohio.
*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.