- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
Regular breeding resident and migrant; occasionally a late migrant will linger in the state through the early winter months. The Great Egret was an uncommon species during the Minnesota Breeding Bird Atlas (MNBBA).
The Great Egret is largely restricted to the southern United States, with year-round populations found in the southeastern states, California, the Caribbean Islands, and along the coasts of Central America and the west coast of South America. Small populations are present throughout the upper Mississippi River valley and central states, in southern Manitoba, Ontario, and Quebec, and in the Pacific Northwest. The egret reaches its highest breeding densities in the lower Mississippi River valley (Figure 1).
Assigned a Continental Concern Score of 7/20 by Partners in Flight and designated a species Not Currently at Risk by the North American Waterbird Conservation Plan.
A year-round resident to medium-distance migrant; the distance travelled south by northern populations may vary from year to year.
Small fish, aquatic invertebrates, amphibians, reptiles, small mammals, and birds.
Usually a stick platform on tall trees and shrubs; occasionally nests on the ground. A colonial nesting species.
Prior to the species’ near extinction by plume-hunters in the late 1800s and early 1900s, the Great Egret was not known as a breeding species in Minnesota. Roberts (1932), however, remarks that it was an occasional straggler into the state. Specific records included sightings in Fillmore County in the 1880s by Dr. Hvoslef; records along the Minnesota River above Fort Snelling during the 1880s by Dr. Hatch (1892); and a record of two birds seen at Heron Lake in 1894. Indeed, more than one hundred years ago, biologists already recognized that juvenile egrets had a propensity to disperse northward once they fledged, with peak numbers often observed during the months of August and September (McCrimmon et al. 2011). Roberts (1932) quoted the following from Cooke and Widman’s 1883 book on bird migration in the Mississippi valley regarding the Great Egret: “The greatest wanderers are the young which in the fall often stray northward into regions where the species is not known to breed.”
By the early 1900s, however, population numbers had plummeted and the late summer stragglers were no longer seen in Minnesota. It would take the birth of a national conservation movement to bring plume hunting to an end, and nearly 25 years of recovery, before the Great Egret returned once again to Minnesota.
The first reports of observations were in August of 1937 at several locations: the Bass Ponds in Hennepin County, near a wetland in Fairmont in Martin County, and at Lake Shetek in Murray County (Rysgaard 1937). Late summer reports would continue to accumulate through the years, with numerous reports from scattered locations throughout southern Minnesota in the 1940s and 1950s. Reports from several northern counties were noted in later years, including Carlton County in 1960 (Gullion 1961), Clearwater County in 1968 (Marshall 1969), and Cook County in 1986 (Webb 1986).
It was not long before the first nesting was reported in the summer of 1938 on East Chain Lake in Martin County (Erickson and Upson 1938). Although this report was a secondhand account, a well-documented report of egrets nesting along the Mississippi River near Winona was investigated by Walter Breckenridge the following year. He found three egret pairs nesting in a mixed-species colony with Great Blue Herons, Double-crested Cormorants, and Black-crowned Night-Herons (Breckenridge 1939).
In the years that followed, Green and Janssen (1975) would report nesting in 17 counties south of a line that stretched from Pelican Lake in Grant County east to Anoka and Washington Counties. Included were nesting reports from well-known, mixed-species colonies at Shields Lake in Rice County (Hanlon 1956) and Lake Johanna in Pope County (Tvrdik 1966). Summer reports of birds seen even further north, including in Clearwater, Otter Tail, and Marshall Counties, led the authors to conclude that the birds would continue to expand northward. Just 12 years later, Janssen wrote that nesting had been confirmed in 29 counties since 1970, including Becker, Marshall, and Otter Tail (Janssen 1987).
About the same time, the Minnesota Nongame Wildlife Program of the Minnesota Department of Natural Resources (MNDNR) issued a series of four technical reports that were 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 a compilation of reports from MNDNR field staff as well as data gathered by local and federal resource agencies and colleges and universities. Published accounts also were compiled. The combined results were summarized by Guertin and Pfannmuller (1985), who reported a total of 22 active Great Egret colonies in the state distributed across 21 counties located primarily in central, southeastern, and northwestern Minnesota from 1981 to 1983. The birds were entirely absent as a breeding species from southwest, north-central, and northeastern Minnesota.
All Great Egret nesting sites were located within mixed-species colonies; 21 were in association with Great Blue Herons and often included Double-crested Cormorants and Black-crowned Night-Herons. A colony that was active for many years on Lake of the Isles was the only site where Great Egrets did not nest with Great Blue Herons but instead nested within a colony of Black-crowned Night-Herons. Of the 22 colonies, 17 supported 50 or fewer Great Egret nests; 3 sites supported 51–200 nests; and 2 sites supported 501–1,000 nests. The 2 largest colonies were on Long Lake in Kandiyohi County (860 nests in 1981) and Egret Island on Pelican Lake in Grant County (743 nests in 1981).
Several years later, Hertzel and Janssen (1998) identified 29 counties where nesting records had been confirmed since 1970. The majority of counties remained in southeastern, central, and northwestern Minnesota.
MNBBA participants reported 815 Great Egret records in 10.2% (483/4,744) of the atlas blocks that were surveyed and in 11.8% (276/2,337) of the priority blocks. Breeding evidence was reported in less than 1% (24) of the surveyed blocks. Two of these blocks actually represented just one breeding locality: Egret Island on Pelican Lake (Figures 2 and 3; Table 1). The birds were reported in 54 of Minnesota’s 87 counties and were confirmed breeding in 19 counties. Two colony sites along rivers were in blocks that straddled multiple counties (the Marsh Lake colony on the Minnesota River and the Pig’s Eye Island colony on the Mississippi River). Colonies were restricted primarily to the central region of the state; none were located north of Becker County. Four breeding counties reported by the MNBBA were additions to Hertzel and Janssen’s 1998 list: Becker, Carver, Lincoln, and Renville. Unlike surveys conducted in the 1980s, several of the colonies where Great Egrets nested did not include Great Blue Herons
Although MNBBA participants originally reported more probable and possible records than are displayed in Figure 3, the vast majority of those records were changed to observed unless documentation supported other breeding evidence codes. Great Egrets can travel far from the breeding colony to their primary foraging territories. Collectively, several studies have reported that the mean distance traveled from the colony site ranges from about 3 km to 12 km (McCrimmon et al. 2011). One study along the Mississippi River reported an average foraging distance of 8.4 km; a study at the Peltier colony in Anoka reported an average foraging distance of 13.5 km (Thompson 1978; 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 in the locality where the birds were observed.
Notable among the atlas results was the report of only one egret colony (Dakota County) along the entire lower Mississippi River, from the Twin Cities south. This may represent a decline in egret colonies along this stretch of the river and/or their inaccessibility to atlas observers. There was evidence of an earlier decline between 1977 and 1988. The number of Great Egret nests along the portion of the Upper Mississippi River National Wildlife and Fish Refuge that borders Minnesota and adjacent waters in Wisconsin declined nearly 50%, from 466 nests in 4 colonies to 276 nests in 6 colonies (Sauer 1991). Yet many of these sites are in backwater sloughs that are difficult to observe and access. Unfortunately no systematic survey of waterbird colonies along the river is regularly conducted, so their current status in this region is unknown.
The MNBBA does provide a reasonable dataset to compare with the compilation prepared by Guertin and Pfannmuller in 1985 to assess changes that may have occurred in the intervening years. The MNBBA data shows that the Great Egret had a nearly identical distribution during the atlas as it did in the 1980s. Guertin and Pfannmuller (1985) reported 22 active colonies that were distributed across 21 counties; the atlas documented 23 breeding localities distributed across 17 counties.
Elsewhere within its breeding range, the Great Egret’s population range has expanded in some areas. Originally decimated by plume hunting over a century ago, the population quickly recovered and the species reoccupied portions of its former breeding range once it was afforded protection through the Migratory Bird Treaty Act. Beginning in the latter half of the twentieth century, the egret expanded further north in New England, the Great Lakes (including Minnesota), and central Canada, and west in Idaho and Oregon (McCrimmon et al. 2011).
*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.
|Breeding status||Blocks (%)||Priority Blocks (%)|
|Confirmed||24 (0.5%)||7 (0.3%)|
|Probable||1 (0.0%)||1 (0.0%)|
|Possible||0 (0.0%)||0 (0.0%)|
|Observed||458 (9.7%)||268 (11.5%)|
|Total||483 (10.2%)||276 (11.8%)|
Like other members of the heron family, the Great Egret requires suitable nest sites located in a landscape with sufficient, high-quality foraging sites. Secluded woodlands with mature trees and surrounded by abundant shallow water habitats, including wetlands, shorelines of lakes and rivers, ditches, and flooded fields, are ideal. Protection from predators also is important, so islands and remote wetlands are preferred (Figure 4).
A highly social species, the majority of Great Egrets in the Upper Midwest nest in mixed-species colonies They frequently nest in the same trees as other waterbirds, especially Great Blue Herons. Two different studies of heron and egret colonies in Minnesota demonstrated that the Great Egret showed a strong preference for tall, mature American Elm trees, selecting some of their highest limbs for nesting (Hanlon 1956; Adams et al. 1973). Small trees and shrubs may be used if other conditions are suitable.
A recent study of the heron rookery on Peltier Lake in Anoka County described the different feeding habitats of the Great Blue Heron and the Great Egret. The heron preferred to feed in larger water bodies (<350 ha) closer to the rookery (median distance of 2.7 km), while the Great Egret demonstrated a preference for small ponds (<25 ha) that averaged 13.5 km from the rookery. The distance travelled reflects, in part, the fact that the smaller wetlands preferred by the egret were also more abundant further from the colony (Custer and Galli 2002).
The Great Egret’s dramatic population decline in the late 1800s and rather spectacular recovery are well documented. Range-wide, population numbers are thought to have plummeted nearly 95%. By 1911, only 1,000–1,500 breeding pairs remained, distributed among 13 colonies in seven states ranging from California to North and South Carolina (Allen 1958).
Once proper protections were in place, numbers began to rebound quickly. In 2002, the North American Waterbird Conservation Plan estimated the continental breeding population of the Great Egret was approximately 185,000 breeding adults (Kushlan et al. 2002).
Although the MNBBA documented colonies where Great Egrets were nesting, only a few observers noted the size of the colonies. An approximate estimate, however, is available from work conducted by Dr. Cuthbert and her colleagues at the University of Minnesota. Since 2004, they have been working with the Minnesota Department of Natural Resources to inventory American White Pelican and Double-crested Cormorant colonies across the state. Their interest was in monitoring how control activities at a handful of cormorant colonies may impact other colonial waterbirds. Because many of Minnesota’s Great Egret colonies also support cormorants, their work is an approximation of the species’ statewide population estimate and trend. Between 2004 and 2015, the number of cormorant colonies with Great Egrets has ranged from 13 to 17 and the number of Great Egret nesting pairs ranged from 2,573 to 3,338, or a total population size of at least 5,100 to 6,600 breeding adults (Hamilton and Cuthbert 2016). Given that only 22 active colonies were reported during the MNBBA, the colonies monitored by the University represent a significant portion of the statewide population.
Although biologists tend to think of the Great Blue Heron as the most abundant colonial waterbird in Minnesota, at the continental scale the Great Egret is believed to outnumber the Great Blue Heron by more than 2:1. Minnesota is on the northern periphery of the egret’s breeding range. Colonies are more abundant further south, and the number of egrets in each colony is considerably larger than found in the Upper Midwest (McCrimmon et al. 2002).
Great Egret populations are also increasing at a faster rate throughout North America than Great Blue Heron populations. The federal Breeding Bird Survey (BBS) has documented a significant average annual increase of 1.91% per year from 1966 to 2015, increasing even higher to 3.40% per year from 2005 to 2015 (Figure 5). Because the species is relatively uncommon in Minnesota, the statistics are less robust, but what information is available also suggests an increasing population (Sauer et al. 2017).
Beyond the initial protective measures that were enacted in the early twentieth century, factors responsible for the species’ continued increase are not well understood. Indeed, biologists have questioned why the egret has not been negatively impacted by the extensive loss and degradation of wetland habitats. This phenomenon has been particularly noticeable in the degraded Everglades ecosystem, where egrets have maintained relatively stable populations while other waterbirds have shown declines (McCrimmon et al. 2002). Overall, this long-lived species appears to show a high degree of adaptability and flexibility that has served it well over the past 150 years.
With steadily increasing populations, the Great Egret has been given a relatively low Continental Concern score of 7/20 and has been classified as a species “not at risk” (Kushlan et al. 2002; Partners in Flight 2017). The species’ vulnerability to warming temperatures has been deemed relatively low (North American Bird Conservation Initiative 2010). Yet as a wetland dependent species, more detailed studies are needed as increasingly arid conditions may threaten quality foraging sites.
Conservation measures for the egret focus primarily on protecting known colonies. The general recommendation is to reduce disturbances at colony sites during the nesting season by establishing buffers of at least 100 m around each colony. At least one study has suggested that such measures are more important at smaller colonies, which may be more sensitive to disturbance and more likely to be abandoned (Kelly et al. 2007). As a recent study at the Peltier Colony in Anoka County demonstrated, protection from predators can be an important conservation measure at rookeries where mammals, such as raccoons, can inflict significant damage and loss (Von Duyke 2006).
Unfortunately, interest in monitoring colonial waterbird populations has waned in many regions, including Minnesota, despite efforts to propose cost-effective and efficient monitoring approaches (Green 1985; McKearnan 1997). Limited conservation dollars are, by necessity, directed at those species deemed to be at greater risk. At present, data collected incidentally at cormorant colonies provides the only statewide index of Minnesota’s colonial waterbird population. Should this effort be discontinued, a small-scale monitoring program for the state’s largest mixed-species colonies would provide a valuable index for monitoring these important sentinels of our wetland communities, including the most striking waterbird of all, the Great Egret.
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