Dickcissel

Regular summer resident and migrant; the Dickcissel was a common species during the Minnesota Breeding Bird Atlas (MNBBA).

The Dickcissel is a grassland species whose breeding range is centered in the Great Plains. It has a history of periodic population irruptions, when birds disperse from their core breeding range in the central plains to grasslands hundreds of miles distant. During years of low abundance, the species is a regular resident in southern Minnesota; during years of high abundance, they may be found nearly statewide. Highest breeding densities are usually found from South Dakota and Iowa south to Oklahoma and Arkansas (Figure 1).

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 long-distance migrant that winters in Central America and northern South America.

An omnivorous species that feeds on arthropods and seeds captured while foraging on the ground and in low vegetation.

An open-cup nest located near the ground or in low forbs and woody shrubs.

The Dickcissel is best known among birders and field biologists as the state’s most irruptive summer resident. Roberts (1932) noted that this little meadowlark look-alike was probably “always present in the summer somewhere in the state” but varied greatly, playing an annual “game of hide and seek”:

There is always a pleasant excitement as to whether or not [the] Dickcissel can be found and where. When it leaves in the fall, after perhaps a season of abundance and intimate acquaintance, it may be lost almost entirely from that locality for no one knows how long.

He told of one such “irruption” that occurred during the summer of 1925. Reports describing a virtual “deluge” of Dickcissels came from all corners of the state, including within the city of Minneapolis, where “it overflowed from the country into the city and in all vacant places in the suburbs.” In more than 50 years of birding, Roberts had never witnessed the species in such abundance. Then, during the following summer of 1926, it was nearly absent from the entire eastern half of the state. Examining records dating back to 1874, he noted that there had been approximately 8 or 10 separate years of high abundance over a period of 55 years.

In the years that followed, there were several published reports noting years of particularly high Dickcissel numbers, including in 1939, 1940, and 1966 (Thompson 1939, 1940; Carlander 1939; Huber 1967). When Green and Janssen (1975) published their updated account of the species’ status, they described its distribution as primarily restricted to southern Minnesota north to Traverse County in the west, and to Chisago County in the east. During years of high abundance, it could be found as far north as Roseau and Lake of the Woods Counties in the northwest, and Pine County in the east.

In his 1987 updated account of the Dickcissel, Janssen noted that even in years of high abundance, the species rarely extended north of southern Crow Wing and Pine Counties. His distribution map identified only 4 southern counties where nesting had been documented since 1970: Martin, Murray, Rock, and Wabasha. Hertzel and Janssen (1998) later added Aitkin, Sherburne, and Winona Counties to the list.

In the winter of 1988, Janssen (1988) reported on a major irruption that occurred during the 1988 breeding season. Reports came in from nearly every county in the state with the exception of Cook, Itasca, Koochiching, Lake, and Lake of the Woods; in St. Louis County there were reports only from the most southern regions near Duluth. Janssen believed that this was the largest Dickcissel invasion he had ever witnessed during 40 years of active birding in the state. His account includes an overview of previous years of high abundance extending from 1952 through 1988. He concluded his review by noting the potential relationship between the extreme drought conditions in Minnesota in 1988 and the Dickcissel’s irruption. Indeed, the drought of 1988 extended throughout much of the western United States and was considered the worst drought since the Dust Bowl era (Minnesota Department of Natural Resources 1989).  Drought conditions in the core of the Dickcissel’s range had been identified by others as a major factor prompting major shifts in distribution (Emlen and Wiens 1965; Sealy 1976).

The Minnesota Biological Survey, begun in 1987, further confirmed that the species’ primary range in the state occurs south of the Minnesota River valley, extending north along the Red River valley into Wilkin, Clay, and Norman Counties. Although it was found as far east as southern St. Louis County, it was sparse outside of the state’s Prairie Parkland Province (Minnesota Department of Natural Resources 2017).

Although a few years of peak abundance occurred following the summer of 1988, it so happened that the summer of 2012, the fourth of five breeding seasons covered by the MNBBA, encompassed the largest Dickcissel irruption ever reported in the state. Not only was it evident in Minnesota, but Dickcissels were abundant across the Upper Midwest and southern Canada (eBird 2012). Documented in detail in an excellent overview by Svingen and Hertzel (2013), reports of Dickcissels came from 86 of Minnesota’s 87 counties; Cook County was the only county where they were not observed. Breeding was confirmed that year in 19 Minnesota counties. Documentation included records from the MNBBA as well as reports to eBird and the Minnesota Ornithologists’ Union. Once again, drought conditions in 2012 throughout the core of the species’ breeding range to the south appeared to be the impetus for peak numbers of Dickcissels to move northward. Svingen and Hertzel (2013) also provide a comprehensive account of former irruptions dating back to the one first reported by Roberts in 1925.

During the five-year span of the MNBBA, observers reported 1,672 Dickcissel records in 20.4% (973/4,774) of the surveyed atlas blocks and in 26.8% (626/2,337) of the priority blocks. Breeding evidence was gathered in 45 blocks (Figures 2 and 3; Table 1). MNBBA participants reported the birds in 78 of Minnesota’s 87 counties, and breeding was confirmed in 30 counties (2 blocks straddled 2 counties each). Svingen and Hertzel (2013) reported nesting in only 19 counties, because the Minnesota Ornithologists’ Union has a narrower list of criteria for accepting confirmed breeding reports than that used by breeding bird atlases (see the introductory section “Reading Species Accounts”). The majority of reports were from the southern portions of the Prairie Parkland and Eastern Broadleaf Forest Provinces. Indeed, with the exception of St. Louis County, all breeding evidence was gathered from counties south of Todd and southern Crow Wing.

Delineating the distribution of a species with such nomadic tendencies as the Dickcissel is challenging. Temple (2002) captured its behavior by delineating the core of the species’ range in the central Great Plains states of Kansas, Missouri, Nebraska, and Oklahoma, where approximately 70% of the population resides. He delineated a much larger peripheral area surrounding the core where the species breeds but usually in much lower numbers. The larger area includes the species’ primary breeding range in Minnesota. Outside of the peripheral area Dickcissels breed even more sporadically. Seasonal shifts in distribution and abundance are common throughout the species’ core and peripheral breeding range. In some years the birds may nest in the southern portion of their range early in the season and then shift northward and initiate a second nesting or renest if earlier attempts failed (Basili et al. 1997).

Svingen and Hertzel (2013) used historical data about the species’ distribution to delineate (1) the Dickcissel’s primary range in the state (the southern third of Minnesota), (2) its range during irruptions that preceded 2012 (the southern half of the state extending north through the Red River valley), and (3) the extent of its distribution during the 2012 irruption (statewide with the exception of the far northeastern and north-central counties).

MNBBA data were used to develop a map depicting the probability of observing Dickcissels statewide (Figure 4). Outside of the Twin Cities metropolitan region, the highest predicted densities are in the southern half of the state with pockets of higher abundance scattered throughout the region, especially south of the Minnesota River valley. In the northern half of the state the probability of detecting Dickcissels is highest in the Red River valley, although their predicted densities are quite low in all but a few areas.

The species’ nomadic tendencies complicate the ability to assess historical changes in distribution. It was established as a common breeding resident in New England and the mid-Atlantic states in the 19th century with records as far north as Canada’s Maritime Provinces and as far south as South Carolina. Now it is only sporadically reported in the region. Large-scale changes in land use are believed to be the primary factor responsible for the change. Clearing the eastern forests for agriculture initially created more habitat opportunities for Dickcissels. Years later, when those lands were either abandoned and succeeded to forest or were more intensively cultivated or developed, habitat opportunities declined (Temple 2002).

*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.

Dickcissels utilize a wide range of open grassland habitats, from hayfields and lightly grazed pastures to native prairies and restored grasslands. Planted cover, including Conservation Reserve Program (CRP) fields, also is suitable, as are roadside ditches and fencerows (Dechant et al. [1999] 2002; Hanowski 1995). During the 2012 irruption in Minnesota, the birds were found in grassy meadows, ditches, weedy patches adjacent to alfalfa fields, and in overgrown brush (Figure 5). They were even found in an open area near downtown St. Paul covered with invasive grasses and forbs (Svingen and Hertzel 2013). Figure 6 summarizes the primary habitats where Dickcissels were found during the MNBBA: croplands, upland grasslands, and developed lands.

Although the species is an obligate grassland species that is native to the prairies of the Great Plains, today native prairie appears to be one of the least preferred habitats. A study in Kansas found that the first sites occupied by territorial males each spring were fallow fields and unmown hayfields; native prairies were left for the later-arriving males (Zimmerman 1993).

Regardless of the type of cover, several structural features appear important for selecting suitable habitat: “dense cover (90–100%), moderate to tall (25–150 cm) vegetation, moderately deep (5–15 cm) litter, and many (>10/ha) elevated song perches” (Temple 2002). A high abundance of forbs seems particularly important, as they provide song perches, nesting cover, nest support, and insect prey (Dechant et al. [1999] 2002). Higher breeding densities are often observed on larger grassland tracts. Although the birds use small tracts, studies have demonstrated that reproductive success is much lower on sites smaller than 10 ha (Dechant et al. [1999] 2002; Temple 2002).

Data gathered from the federal Breeding Bird Survey (BBS) (Sauer et al. 2017) have been used to generate a breeding population estimate of 27 million breeding adults (Rosenberg et al. 2016). In 2013, when the continental estimate was significantly lower, the statewide estimate for Minnesota was 170,000 birds, or 0.9% of the continental population (Partners in Flight Science Committee 2013). Applying that same percentage to the most recent continental estimate yields a statewide estimate of 243,000 adults. MNBBA data generated a significantly higher estimate of 1.2 million adults. The high estimate, however, was based on data that included one major irruption, in 2012.

The average number of Dickcissels reported on BBS routes in Minnesota each year is 6. In the heart of their range in southern Minnesota, it is not uncommon to detect approximately 30 birds per route. Nonetheless, these numbers are still low compared to the number of birds detected farther south. In Kansas, an average of 186 birds are detected per route, 96 in Missouri, and 98 in Oklahoma. Immediately south of Minnesota, Iowa reports an average of 144 Dickcissels per route (Sauer et al. 2017). Local breeding densities in the central plains states average more than 50 nests per 40 ha (Temple 2002). Bryan and Best (1994) reported 110 nests per 40 ha in Iowa; Harmeson (1974) reported 67 nests per 40 ha in Illinois. Typically numbers are much lower in peripheral breeding areas such as Minnesota. On CRP lands in western Minnesota, Hanowski (1995) found 0.5 pairs per 40 ha.

Throughout its breeding range, the Dickcissel has demonstrated a long-term population decline of 0.36% per year since 1966. The decline was steepest in the first 20 years of the survey, declining nearly 30%, but appears more stable since the 1980s (Sauer et al. 2017; Temple 2002). In the late 1970s, some biologists were predicting the species’ demise, but its adaptability to restored grasslands and agricultural fields has resulted in a much more sustainable future. Current population numbers, however, are at least two-thirds of those seen in the late 1960s (Temple 2002).

Minnesota’s location on the northern periphery of the species’ range, where population numbers may vary significantly from year to year, is well illustrated by the statewide BBS trend. Overall, the species has experienced a statistically significant annual decline of 6.00% per year since 1966, and an even higher rate of decline of 10.40% per year from 2005 to 2015 (Figure 7). Throughout this time, however, numbers have fluctuated widely. The population trend in the core of the species’ breeding range is likely a better barometer of the overall population trend. The majority of the core breeding range occurs within the Eastern Tallgrass Prairie and Central Mixed Grass Prairie regions. In both regions, Dickcissels experienced a significant annual decline of 1.01% per year from 1966 to 2015 (Sauer et al. 2017). Throughout the BBS survey region, the population is estimated to have experienced a cumulative decline of 14% from 1970 to 2014 (Rosenberg et al. 2016).

More intensive agricultural practices that have converted grasslands and hayfields to row crops have certainly decreased the availability of suitable habitat for Dickcissels. Unfortunately, many suitable sites, such as hayfields and roadsides, may be mowed before the young have fledged. Because the Dickcissel is a late nester, this can be more problematic for them than for many other grassland species. Nests in roadsides and other edge habitats also may experience high rates of depredation (Dechant et al. [1999] 2002).

An even greater concern is the threat experienced on the species’ wintering grounds. The core wintering area is in central Venezuela, where Dickcissels are considered a major agricultural pest, feeding on fields of rice and sorghum. Although most farmers now use nonlethal methods to scare the birds away, lethal methods are still employed by some and can result in significant mortality (Temple 2002).

Although its future was in doubt nearly 40 years ago, today the Dickcissel’s future seems considerably more secure. Partners in Flight has assigned it a conservation score of 11/20 (Rosenberg et al. 2016). Threats on the wintering grounds are the primary factor contributing to this moderately high score. In light of its continued population decline, it also has been designated a Species in Greatest Conservation Need in Minnesota (Minnesota Department of Natural Resources 2015). As is the case with many species dependent on the Great Plains, warming temperatures may pose some challenges to the Dickcissel. The North American Bird Conservation Initiative (2010) has rated its vulnerability to climate change as moderate.

On the breeding grounds, specific management recommendations focus on minimizing disturbance during the nesting season, thus delaying mowing and burning activities until late summer. Management work should be conducted on a rotational system so a mosaic of habitats is always available at a given site. Dickcissels will tolerate some shrub cover, but woody vegetation needs to be controlled before a site becomes totally overgrown. The key to providing suitable habitat is to control succession and insure an abundance of dense, moderately tall vegetation with abundant forbs and a rich, deep litter layer (Dechant et al. [1999] 2002).