Dolichonyx oryzivorus

A 18-cm-long bird with a stout, relatively short, pointed bill and sharply pointed tail feathers; breeding male is black below, with a buff to whitish hind-neck, white scapulars, and white rump; early spring male has pale feather edgings; breeding female is buffy with dark streaks on the back, rump, sides, and head; juvenile resembles breeding female but lacks streaks below; fall adults and immatures resemble breeding female but are darker above and richer buff below (NGS 1983). Strongly sexually and seasonally dimorphic with respect to body mass; mean body weights: breeding females, 29.1 g; breeding males, 33.9 g; migrating females, 39.9 g; migrating males, 51. g (Martin and Gavin 1995).

Breeding habitat includes tall grass areas, flooded meadows, prairie, deep cultivated grains, and hayfields (AOU 1998). In New York, old hayfields, at least 8 years since planting and including a minimum of alfalfa, were important nesting habitat (Bollinger and Gavin 1992). Nests are on the ground in small hollows in areas of concealing herbaceous vegetation. Individuals tend to return to breed in the same area in successive years, especially if that site has had good bobolink productivity (Bollinger and Gavin 1989).

This species generally selects habitat with moderate to tall vegetation, moderate to dense vegetation, and moderately deep litter (Tester and Marshall 1961, Bent 1958, Harrison 1974, Bollinger 1995), lacking oody vegetation (Sample 1989, Bollinger and Gavin 1992). It is found in native and tame grasslands, haylands, lightly to moderately grazed pastures, no-till cropland, small-grain fields, oldfields, wet meadows, and planted cover (e.g., Conservation Reserve Program [CRP] fields, Permanent Cover Program [PCP] fields, and Dense Nesting Cover [DNC]) (Bent 1958; Speirs and Orenstein 1967; Birkenholz 1973; Harrison 1974; Skinner 1974, 1975; Stewart 1975; Joyner 1978; Johnsgard 1979, 1980; Faanes 1981; Kantrud 1981; Kantrud and Kologiski 1982; Renken 1983; Huber and Steuter 1984; Basore et al. 1986; Renken and Dinsmore 1987; Bollinger 1988, 1991, 1995; Sample 1989; Bollinger et al. 1990; Messmer 1990; Herkert 1991a, 1994a,1997; Bollinger and Gavin 1992; Bock et al. 1993; Johnson and Schwartz 1993; Dhol et al. 1994; Hartley 1994; Jones 1994; King and Savidge 1995; Madden 1996; Patterson and Best 1996; Prescott and Murphy 1996; Best et al. 1997; Dale et al. 1997; Delisle and Savidge 1997; McMaster and Davis 1998; Schneider 1998). Commonly it occurs in areas with high percent grass cover and moderate percent forb cover (Wiens 1969, Skinner 1974, Renken 1983, Renken and Dinsmore 1987, Sample 1989, Herkert 1994a, Madden 1996). Bollinger (1988, 1995) noted preference for haylands with high grass-to-forb ratios and avoidance of haylands with high legume-to-grass ratios; however, a forb component was beneficial for nesting cover.

Within mixed-grass pastures in North Dakota, abundance was positively associated with percent grass cover, litter depth, density of low-growing shrubs (western snowberry, Symphoricarpos occidentalis; silverberry, Elaeagnus commutata), vegetation density, and plant communities dominated by Kentucky bluegrass (Poa pratensis) and native grasses (Stipa, Bouteloua, Koeleria, and Schizachyrium) (Schneider 1998). Abundance was negatively associated with percent clubmoss (Selaginella densa) cover, bare ground, and plant communities dominated solely by native grass. Strongest vegetational predictors of the presence of bobolinks were decreasing bare ground, increasing litter, and increasing vegetation density. Madden (1996) found that the best predictors of occurrence in North Dakota mixed-grass prairie were increasing amounts of forb and grass cover, decreasing amounts of shrub cover, and decreasing frequency of native grasses.

In Illinois tallgrass prairie fragments, the best predictors of occurrence were mean number of live forb contacts, mean vegetation height, and mean grass height (Herkert 1994a). In another Illinois study, occurred only in patches of Kentucky bluegrass and were absent from tallgrass prairie (Birkenholz 1973).

In Nebraska, abundance in CRP planted to cool-season grasses was significantly and positively correlated with percent litter cover and negatively correlated with vertical density of vegetation (measured using a Robel pole) (Delisle and Savidge 1997). In tame CRP grasslands in Iowa, abundance was positively correlated with litter cover and grass canopy cover and negatively correlated with forb cover and the horizontal patchiness of vegetation (Patterson and Best 1996). Abundance in Wisconsin was highest in cool-season grasses, followed by wet pastures, bluegrass (Poa)/quackgrass (Agropyron repens) communities, and alfalfa (Medicago sativa/grass hayfields (Sample 1989). In New York tame hayfields, increased in abundance as the hayfields aged (Bollinger 1988, 1995). Older hayfields (more than 3 years old) were characterized by sparse, patchy, grass-dominated vegetation and high litter cover.

In Nebraska, boblinks nested in wet prairie, alfalfa, upland native prairie, domestic hayland, and wheat (Faanes and Lingle 1995). In Iowa they nested under or near native bluestem (Andropogon or Schizachyrium not specified) or Kentucky bluegrass (Kendeigh 1941). In Wisconsin boblinks nested at the bases of large forbs (Martin 1971). In Montana, nested in a wet-meadow pasture (Silloway 1904). In Ontario, they nested in a weedy meadow near a wetland; nests were built in the litter layer, had a canopy of dead grasses, and were surrounded by living vegetation 33-41 centimeters tall (Boyer and Devitt 1961, Joyner 1978). Boblinks have been found nesting in CRP fields in Iowa and Michigan (Best et al. 1997).

Boblinks occasionally nest in cropland. In Iowa, they nested at low densities in untilled fields of corn that were idle in the fall and spring and contained year-round crop residue, rather than in tilled fields or strip cover (Basore et al. 1986). In Wisconsin, a few were found in small-grain fields, but none were found in rowcrops (Sample 1989). Graber and Graber (1963) reported fairly heavy use of small grain fields in Illinois. The species was absent from cropland in Saskatchewan and Manitoba (Hartley 1994, Jones 1994).

During the nonbreeding season, boblinks also occur in rice fields, marshes, and open woody areas (AOU 1983).
In Argentina, bobolinks primarily use natural wet grassland habitats associated with main rivers and huge marshes (Di Giacomo et al. 2005).

Bobolinks often are in large flocks during northward migration.

Clutch size is four to seven (usually five to six). Incubation, by female, lasts 11-13 days. Young are tended by both parents, leave nest at 10-14 days (still unable to fly). In some areas, individual females very rarely may produce a second clutch (unsuccessful) after the first brood fledges (Gavin 1984).