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Nesting Ecology and Nesting Habitat Requirements of Ohio's Grassland-nesting Birds: A Literature Review

Results and Discussion


Dickcissel populations are renowned for dramatic fluctuations (Gross 1956, Hurley and Franks 1976, Fretwell 1986, Janssen 1988, Herkert 1991). In Ohio, at the eastern edge of their breeding range, population fluctuations are quite noticeable. Sizable breeding populations are often followed by precipitous declines and populations may remain low for 15 years or more (Peterjohn 1989, Peterjohn and Rice 1991).

Breeding dickcissels return to Ohio during the last half of May and early June. Most nests are constructed in June and most young fledge in July and early August. Dickcissels begin leaving Ohio during August and most have migrated south by the first half of September (Peterjohn 1989).

Dickcissels spread eastward from the Great Plains during the nineteenth century, and became established in Ohio during the mid-1800s. Throughout the twentieth century, dickcissels have been rare to locally uncommon summer residents in the western half of Ohio (east to Scioto, Pike, Ross, Pickaway, Fairfield, Licking, Knox, Richland, Huron, and Erie counties) and casual visitors to the eastern half. Although the statewide population was unusually large during the Ohio Breeding Bird Atlas Project (1982-87), exceeding 500 singing males, <100 dickcissels reside in Ohio during most years (Peterjohn and Rice 1991).

In Ohio, most dickcissel males established territories in clover and alfalfa hayfields, weedy undisturbed fields, grassy pastures, and reclaimed surface mines planted to mixed grasses and sweet clover (Peterjohn 1989, Peterjohn and Rice 1991). Several researchers reported dickcissels nesting in hayfields (Gross 1921, Stoddard 1922, Tabor 1947, Graber and Graber 1963, Emlen and Wiens 1965, Hurley and Franks 1976, Fretwell 1977, Brooks 1988, Sample 1989), undisturbed (idle) grasslands (Gross 1921, Wetmore and Lincoln 1928, Graber and Graber 1963, Meanley 1963, Brooks 1988, Brown 1988, Sample 1989), old fields (Kendeigh 1941; Zimmerman 1966, 1971, 1982, 1983; Harmeson 1974; Finck 1984), CRP grasslands (Sample 1989; Lauber 1991; Johnson and Schwartz 1993a,b; Reynolds et al. 1994), and pastures (Gross 1921, Emlen and Wiens 1965, Zimmerman 1971, Harmeson 1974, George et al.1979). Kendeigh (1941) reported that dickcissels were not characteristic of the tallgrass prairie but instead preferred seral stages and disturbed areas with sparser vegetation. However, many studies reported dickcissels nesting in native and restored tallgrass prairie (Aldrich 1948; Overmire 1962; Wiens 1963; Hurley and Franks 1976; Fretwell 1977; Brooks 1986; Blankespoor 1980; Zimmerman 1983; Finck 1984; Laubach 1984; Sample 1989; Herkert 1991; Volkert 1992). Dickcissels also were reported nesting in meadows (Dambach and Good 1940, Good and Dambach 1943, Hergenrader 1962), woodlands and shrublands (Graber and Graber 1963, Wiens 1963, Zimmerman 1971, Brooks 1988), railroad rights-of-way (Braband 1984), roadside rights-of-way (Hergenrader 1962, Meanley 1963, Fretwell 1977, Warner 1992), grassed waterways in rowcrop fields (Bryan and Best 1991, 1994), marshes (Tabor 1947), small grains (Gross 1921, Graber and Graber 1963, Emlen and Wiens 1965, Hurley and Franks 1976, Laubach 1984), and cultivated cropland (Gross 1921; Good and Dambach 1943; Emlen and Wiens 1965; Bryan and Best 1991,1994). Johnson and Schwartz (1993b) reported that dickcissel abundance was significantly higher in CRP fields than in adjacent cropland.

Male dickcissels established nesting territories in areas with the tallest, densest vegetation (Rotenberry and Wiens 1980, Sample 1989) and density of territorial males was positively related to the volume (height x cover) of herbaceous vegetation (Zimmerman 1971). Zimmerman (1971) reported that the vegetation within dickcissel nesting territories was taller and/or denser than the vegetation outside territories. Vegetation in bachelor territories was shorter and sparser, and percent forb cover was lower, than that in mated male territories (Zimmerman 1966).

Dickcissels sang from herbaceous or woody perches that extended above the average layer of the vegetation (Zimmerman 1971). In Wisconsin, dickcissels preferred singing from tall (>3 m) trees or shrubs, but also sang from tall forbs and utility wires (Sample 1989). Height and density of woody vegetation did not influence male dickcissel density in Kansas, but the absence of perches above the general vegetation canopy precluded use of an area by this species (Zimmerman 1971).

Little data exist on the vegetative characteristics of dickcissel nesting territories. Mean vegetative characteristics of habitats occupied by nesting dickcissels in Wisconsin were <1% woody cover, 74% herbaceous vegetation cover, 17% litter cover, 9% bare ground, 63-cm maximum vegetation height, and 19-cm vegetation height-density (Sample 1989). Rotenberry and Wiens (1980) found a positive correlation between dickcissel abundance and litter depth. Kendeigh (1941) reported that litter depth at dickcissel nest sites averaged 5-8 cm.

Nests are built on or near the ground, either in clumps of herbaceous vegetation or in crotches of woody vegetation. Forbs appear to be preferred over grasses as nesting substrate. High densities of nesting dickcissels were associated with high forb coverage in several studies (Gross 1921; Dambach and Good 1940; Kendeigh 1941; Tabor 1947; Emlen and Wiens 1965; Zimmerman 1966,1971,1982; Harmeson 1974; Zimmerman and Finck 1982; Finck 1984; Sample 1989). George et al. (1979) reported that a light scattering of forb in warm-season grass pastures greatly enhanced dickcissel nesting densities. In Iowa, Bryan and Best (1994) noted that the occurrence of a dickcissel nest was 3.9 times more likely in waterways with high forb cover than in those with low or no forb cover. In Kansas, Zimmerman (1966) noted that prior to the full development of forbs (15 Jun), most dickcissel nests were located in grass, but after 15 June, most nests were placed in forbs. Zimmerman (1971) attributed higher dickcissel nesting densities in old fields compared to tallgrass prairie to the former's greater forb cover. Harmeson (1974) and Rotenberry and Wiens (1980), however, associated nesting dickcissels with dense grass cover. Herkert (1991) found no correlations between dickcissel abundance and percent forb or grass cover.

Zimmerman (1982) reported that the net productivity (fledglings/nest) of dickcissels was higher in old fields than in tallgrass prairie. A higher volume of vegetation in old fields permitted higher nesting densities and a greater forb component increased food availability compared to tallgrass prairie. Schartz and Zimmerman (1971) reported that insect abundance was highest in forbs (118 individuals/m2), 38% lower in grasses (73 individuals/m2), and 53% lower in wheat (55 individuals/m2).

Since the mid-1900s, the dickcissel's breeding range has contracted largely because of increased hay harvesting during the nesting season (Hurley and Franks 1976). Dickcissels occurred in highest densities on recently mowed (cut Jan-Apr) grasslands with relatively short vegetation in Illinois (Herkert 1991). However, Bryan and Best (1994) reported that dickcissel nesting densities were higher in unmowed waterways (844 nests/100 ha) than in waterways mowed the previous year (114 nests/100 ha). They noted that dickcissels nested successfully only in the taller vegetation provided on unmowed waterways.

Fretwell (1977) and Herkert et al. (1993) recommended that areas managed for dickcissel nesting habitat not be grazed because of the species' preference for tall, dense vegetation. Grazing may increase the susceptibility of dickcissel nests to brown-headed cowbird (Molothrus ater) parasitism. The percentage of dickcissel nests parasitized by cowbirds ranged from 31-33% in ungrazed old field habitat (Overmire 1962, Wiens 1963) to 50-53% (Hergenrader 1962, Hill 1976), and even 95% (Elliott 1978), in grazed prairie.

Laubach (1984) concluded that burning tallgrass prairie prior to 15 April in Iowa did not delay nesting of dickcissels. Dickcissel abundance was similar on grasslands the first, second, and third or more growing season post-fire in Illinois (Herkert 1991, 1994a). In Kansas, however, dickcissel abundance was 12% higher on unburned than burned tallgrass prairie (Zimmerman 1992).

Based on data from Illinois and Missouri, Herkert et al. (1993) classified the dickcissel as having a low sensitivity to habitat fragmentation, being encountered on habitat fragments of all sizes. Dickcissel abundance was not related to grassland area in Illinois (Herkert 1994c). Samson (1980) estimated that 1-10 ha of contiguous grassland habitat represented the minimum area required to maintain a viable breeding population of dickcissels. In southwestern Ohio, dickcissels were found on 3 fields that averaged 12 ha (D. Nolin and J. Ritzenthaler, unpubl. data). Dambach and Good (1940) noted that dickcissels nested in large meadows but not in grassy strips within cultivated rowcrops in southern Ohio.

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