Distribution: The breeding range of the bobolink, Dolichonyx oryzivorus, is an east-west band across the northern United States and southern Canada between the 50th and 39th parallels, from British Columbia, Washington, and Oregon, to Newfoundland, Nova Scotia, and Maine. Its distribution is fairly continuous in the East but patchy in the West. Isolated breeding populations occur in northern Utah and Nevada, central Washington, and eastern Arizona (Martin and Gavin 1995). Bobolinks do not breed in most of Utah. They occur in low abundance and in isolated patches primarily in the northern half of the state. Bobolinks have been found consistently and are likely to breed or have bred near Logan, Brigham City, Kamas, Heber, Morgan, Mountain Green, Huntsville, West Layton, Provo and at the south end of Bear Lake (Hayward et al. 1976, Smith 1995). Bobolinks have also been reported from Deseret Ranch, Kaysville, West Springville, Goshen, Ibapah, Callao, Fish Springs, Skull Valley, Beaver County (Kaufmann Ranch), Washington Fields, and Lytle Ranch (Hayward et al. 1976, M. Webb pers. comm.), though the breeding status of birds at these sites is uncertain. Bobolinks were historically common in northern Utah; Hayward et al. (1976) indicated that "all of the early investigators visiting Utah prior to the turn of the century found this bird present and in considerable numbers." Bobolinks are now considered to be rare (Walters and Sorensen 1983) and somewhat erratic, probably not occurring during drought periods (Behle et al. 1985). Bobolinks winter primarily in southern South America from eastern Bolivia and southwestern Brazil through Paraguay and Argentina to Buenos Aires; wintering birds have also been recorded in portions of western South America (Martin and Gavin 1995).
Ecology: Bobolinks have one of the longest annual migrations of any North American songbird. These Neotropical migrants travel about 20,000 km (12,500 mi) from their North American breeding grounds to their "wintering" grounds in southern South America. Their nonbreeding season actually occurs in the spring of the southern hemisphere. Bobolinks spend approximately half of each year in migration. Bobolinks typically arrive in Utah in early to mid May and probably begin southerly migration around mid August, though some birds may still be present through September (Behle and Perry 1975). Pettingill (1983) commonly noted wintering birds on the Galapagos Islands and hypothesized that bobolinks that breed in western United States might winter in western South America. However, this has not been researched.
Males arrive on the breeding grounds in early to mid May about one week before females. Courtship generally takes less than 3 days and all pairs within a patch are formed within a few days, some within a few hours. Males are strongly polygynous often taking 2 (sometimes 3, rarely 4) females. The occurrence and degree of polygyny may depend on habitat quality and/or food abundance.
Nest construction begins about a week after female arrival and takes one to two days to complete. Females build nests on the ground by first clearing a nest-sized area of vegetation, exposing the bare ground beneath; if not in a natural depression, the area is often scraped by the female. The depression is then filled with a cup of coarse grasses and weed stems, with an inner lining of finer grasses and sedges. Beginning one to two days after the nest is complete, eggs are layed at a rate of one per day. Average clutch size is five, though three to seven eggs are not uncommon. Incubation begins with the second to last egg and is done by the female for about 11-13 days. Hatching occurs over a 20-30 hr period, with most eggs hatching in the first two to five hourrs (hatching of the last egg layed may be delayed for many hours). Nestlings are fed exclusively invertebrates by both males and females. Male contributions may focus primarily on the nest of his first mate, or may be spread among nests of all mates (usually 2). Fledging occurs in 10-11 days (8-9 days if disturbed), though short flights are not performed until day 13. Both adults feed fledglings. Pairs will often renest after failure and double brooding is unusual but has been recorded. Often within about 6 days of fledging, pairs and their broods will flock together with other family units. Adults feed their own young in the flock, and the flock grows throughout the season as more nestlings fledge. The flock remains relatively coherent until, and possibly after, migration has begun.
Habitat Requirements: Bobolinks in the West nest and forage in wet meadow (grasses and sedges), wet grassland, and irrigated agricultural (primarily pasture and hay fields) areas. These habitats, particularly wet meadows, tend to be associated with riparian or wetland areas. Precise habitat characteristics have not been well studied in the West. Bobolinks nesting in the East appear to be most successful in large (30 ha or more), old (8 years or older) hay fields (Bollinger and Gavin 1992). Old hay fields typically have high proportions of grass (or grass and forbs) and low proportions of alfalfa; pure alfalfa fields were not considered suitable breeding habitats. Nest sites tend to be in wet habitats, but also occur in transitional areas between wet and dry areas. Nests are almost always built on the ground and are often located at the base of large forbs. Although grass usually makes up a large portion of the general nesting area, nests are rarely located in grass, but are instead located in forbs and sedges.