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Photo by Nicky Davis
Photo Copyright Nicky Davis
Bobolink
Dolichonyx oryzivorus
NatureServe conservation status
Global (G-rank): G5
State (S-rank): S2B
- Reason: Six occurrences with confirmed breeding by this species are known in Utah. 15 other occurrences perhaps suggestive of possible breeding in Utah are also known.
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General information
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.
Species range
Hayward et al. (1976) stated that in Utah this species is "seemingly confined mainly to the valleys west of the Wasatch Front" in north-central Utah. Walters and Sorensen (1983) similarly indicated its brreeding occurrence in extreme north-central Utah as well as summer records from the extreme northwest corner of the state (extreme northwestern Box Elder County), but without documented breeding. Confirmed breeding occurrences of this species are known in six Utah counties, all in the north-central part of hte state: Cache, Morgan, Davis, Summit, Wasatch, and Utah.
Migration
Bobolinks arrive in northern nesting areas late April-early May; males arrive a few days to a week before females (Terres 1980). Bobolinks are uncommon migrants in fall in Puerto Rico and the Virgin Islands, rare in spring (Raffaele 1983). Migration occurs mostly via the West Indies; small numbers reach Middle America (Ridgely and Gwynne 1989). Bobolinks are rare fall migrants in Costa Rica, mid-September to October, and are basically absent in spring (Stiles and Skutch 1989). They are transient in Colombia, mainly early September-late November and early March to mid-May (Hilty and Brown 1986).
Habitat
Hayward et al. (1976) wrote of this species in Utah: "Its habitat is restricted almost entirely to wet, short grass fields and pastures." Behle et al. (1985) stated that in Utah this species "frequents wet pasturelands and fields and probably in perods of drought the species is not present."
Food habits
Diet includes insects, seeds, grain (Terres 1980); mainly seeds (Stiles and Skutch 1989).
Ecology
Bobolinks often are in large flocks during northward migration.
Reproductive characteristics
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).
Threats or limiting factors
Probably the greatest threats to this species in Utah are habitat loss and degradation through draining of wetlands and conversion to agricultural, industrial, and residential development. Other agricultural practices, such as pesticide use, may also be threats. Martin and Gavin (1995) considered hay-cropping (i.e., mowing) to be a serious threat to the species: ". . . [H]ayfields now are cut 2-3 wk earlier than they were in 1940s and 1950s, with mowing coinciding with peak nesting period." They cited one study in which "100% of nests with eggs and young nestlings affected by mowing were abandoned or destroyed . . .." These authors also considered flooding of lowland meadows and other nesting habitat to be an important threat to this species.
References
- Text modified from: Parrish, J. R., F. P. Howe, and R. E. Norvell. 1999. Utah Partners in Flight draft conservation strategy. UDWR publication number 99-40. Utah Partners in Flight Program, Utah Division of Wildlife Resources, Salt Lake City.
