Dickcissel Spiza americana

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Life History Groupings:

Breeding Habitat:Grassland

Nest Type:Open-cup nesting passerine

Migration Status:Neotropical migrant

Nest Location:Ground-low nesting

Species Account:

The Dickcissel is an enigmatic grassland bird, whose status and distribution have always been confounded by its pattern of irregular movements. This species is believed to have originally occupied the tall grass and mixed prairies of the eastern and central Great Plains. Historical changes in its breeding range have been associated with large-scale changes in agricultural land use practices (Hurley and Franks 1976). Deforestation allowed this species to spread eastward during the nineteenth century (Peterjohn and Rice 1991). Additionally, Dickcissels were well established summer residents along the Atlantic coastal plain during that century. This population largely disappeared late in the nineteenth century (Gross 1921), so little is known about its origins, status, and distribution.

Even though most native tall and mixed grass prairies have been destroyed, breeding Dickcissels remain most numerous on the eastern and central Great Plains from Iowa and southern South Dakota south to Missouri and Texas (Relative Abundance Map). Their abundance declines rapidly towards the eastern and western edges of this range. A few records are scattered along the Atlantic coastal plain, where this species remains a rare and sporadic summer resident.

While Dickcissels tend to be scarce and locally distributed at the peripheries of their range, periodic influxes from elsewhere in their range can cause these populations to exhibit considerable annual fluctuations in abundance. These influxes near the periphery of the range are inversely correlated with habitat suitability in the southern portion of their normal breeding range (Fretwell 1986). An example of these population movements occurred during 1988, when a severe drought in the Great Plains produced a noticeable influx into Michigan, Pennsylvania, and other eastern states (Brauning 1992, Brewer et al. 1991). Additionally, Fretwell (1986) theorized that some females may be double-brooded, breeding in the southern Great Plains during late spring and again farther north during the summer. Such movements would also complicate the analyses of population trends, especially if they do not occur every year.

Regional influxes and other large-scale population movements can obscure the overall trends of this species, especially in states/provinces and physiographic strata. However, Dickcissel populations have generally declined since the mid-1960s. Over the entire survey period, significant increases are restricted to Arkansas, Oklahoma, and the Drift Prairie (S37) stratum; populations in 6 states, 10 strata, the Eastern and Central BBS regions, U.S., and survey-wide have declined (Trend List). During the 1966-1979 interval, all significant trends in states/provinces, strata, and regions with adequate sample sizes are declines. After 1980, declines are limited to Missouri and 3 strata while 6 states, 6 strata, the Central BBS Region, U.S., and survey-wide populations increased. The geographic patterns to the long-term trends are not uniform (Trend Map). Declines are most prevalent in the northern portion of the range, particularly from Ohio west to Minnesota, Iowa, and Missouri, and also from Nebraska north into North Dakota. Declines also prevail in central Texas. Increases predominate from northern Texas through Oklahoma into Kansas, and from Arkansas and Louisiana east into Alabama and Tennessee.

The survey-wide annual indices exhibit a distinct decline through the late 1970s, followed by variable but fairly stable counts (Survey-wide Annual Indices). Declines during the first 10 years of the BBS are evident in the Eastern and Central BBS regions, but populations in both regions have been reasonably stable since the early 1980s (Eastern BBS Region Annual Indices) (Central BBS Region Annual Indices). States/provinces and physiographic strata show a variety of temporal patterns in population trends. Some states mimic the regional trends with declines through the late 1970s or early 1980s, followed by fairly stable trends; Illinois and Louisiana are examples (Illinois Annual Indices) (Louisiana Annual Indices). States such as Arkansas, Kansas, and Oklahoma show several periods of increases and declines since 1966, but the population "highs" and "lows" are not correlated between these states (Arkansas Annual Indices) (Kansas Annual Indices) (Oklahoma Annual Indices). The Iowa population declined through the early 1980s, then markedly increased followed by another decline (Iowa Annual Indices). Even trends in adjoining strata tend to be variable with no apparent correlations between increases and declines, as shown by the Osage Plain-Cross Timbers (S33), High Plains Border (S34), and Rolling Red Prairies (S35) strata (Osage Plain-Cross Timbers Annual Indices) (High Plains Border Annual Indices) (Rolling Red Prairies Annual Indices).

Most Dickcissels winter in northern South America and sporadically in Central America. While stragglers are regularly encountered on CBCs, especially in eastern and central North America, these limited data are insufficient to establish population trends during that season.

A number of factors have contributed to the trends in Dickcissel populations. This species is well adapted to residing in agricultural landscapes, inhabiting hayfields, pastures, weedy fallow fields, and the weedy margins of ditches and roadsides. However, the conversion of these habitats into cultivated fields and the more frequent mowing of hayfields contributed to the declines in some areas (Fretwell 1986). Brood parasitism by Brown- headed Cowbirds has been shown to negatively impact recruitment of Dickcissels, as could increased nest predation in certain habitats (Zimmerman 1983, 1984). Factors on their winter range are also believed to be important (Fretwell 1986). Fretwell (1977) indicated that food availability on the winter range influences the numbers of Dickcissels returning the following spring, and may favor the survival of males over the survival of females. Changing land use practices as well as persecution may also be affecting Dickcissels during the winter months in northern South America.

Literature Cited

Brauning, D.W., ed.  1992. Atlas of breeding birds in Pennsylvania.                   
     Univ. of Pittsburgh Press, Pittsburgh, PA.  484 pp.                              
Brewer, R., G.A. McPeek, and R.J. Adams, Jr.  1991.  The atlas of                     
     breeding birds of Michigan.  Michigan State Univ. Press, East                    
     Lansing, MI.  594 pp.                                                            
Fretwell, S.D.  1977.  Is the Dickcissel a threatened species?  Am.                   
     Birds 31: 923-932.                                                               
Fretwell, S.D.  1986.  Distribution and abundance of the                              
     Dickcissel.  Current Ornith. 4:211-242.                                          
Gross, A.O.  1921.  The Dickcissel (Spiza americana) of the                           
     Illinois prairies.  Auk 38:1-26, 163-184.                                        
Hurley, R.J., and E.W. Franks.  1976.  Changes in breeding ranges                     
     of two grassland birds.  Auk 93:108-115.                                         
Peterjohn, B.G., and D.L. Rice.  1991.  The Ohio breeding bird                        
     atlas.  Ohio Dept. Natur. Resour., Columbus, OH.  416 pp.                        
Zimmerman, J.L.  1983.  Cowbird parasitism of Dickcissels in                          
     different habitats and at different nest densities.  Wilson                      
     Bull. 95:7-22.                                                                   
Zimmerman, J.L.  1984.  Nest predation and its relationship to                        
     habitat and nest density in Dickcissels.  Condor 86:68-72.