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Dolichonyx oryzivorusbobolink

By Amber Simon

Geographic Range

Bobolinks (Dolichonyx oryzivorus) have breeding grounds across much of the northern United States and southern Canada, from 40° N to 50° N. Each year, many of the same birds return to the same fields for nesting. During the winter, bobolinks migrate to South America; they can be found from 8° S to 32° S, in Brazil, Uruguay, Paraguay, and northern Argentina. Around early August, bobolinks begin their fall migration south to their winter grounds, nearly 9,500 km from their nesting grounds, one of the longest migration routes of all Western Hemisphere passerines. Eastern populations typically head southeast, while western populations are smaller and very little is known of their migration patterns. Their migration occurs across the southeastern United States, down through the Caribbean, and into South America. Bobolinks can be found in their breeding region from about late April to September, depending on their range. (Gavin, 1984; Hamilton, 1962; Martin, 1973)

Habitat

Bobolinks are found in grassy fields and wetlands, earning them the nickname, “reedbirds”. They nest in hay fields, primarily in the eastern and Midwestern portion of the United States. Their winter region includes the grassy fields of Brazil, Uruguay, Paraguay, and northern Argentina. During migration, they stop along the way in rice fields, which has also earned them another nickname, “rice-birds”. Nesting survival rate is greater in areas near old fields and pastures. These birds select areas with tall grasses, away from woodlands, and often nest in the same areas each year. (Bollinger and Gavin, 2004; Bollinger, et al., 1990; Dechant, et al., 2001; Gavin, 1991; Lawyer, 1918)

  • Aquatic Biomes
  • lakes and ponds

Physical Description

Bobolinks exhibit sexual dimorphism during the breeding season. Because male breeding plumage is black, they blend into their tall grass habitat. In breeding plumage, males display an extensive white patch down their backs with a buttery rear crown and shiny black bill. When they are not in breeding plumage, males look very similar to females. Females and immature males have pale bills. All sexes and age-classes have short, cone-shaped bills. Female and immature male bobolinks are yellowish brown with black stripes falling behind the eyes and continuing down their back. There is a stripe above their eyes and in the center of their crown. Their wings are brown with stripes and their tails are short, pointy, and brown. (Chapman, 1890; Sibley, 2003)

  • Sexual Dimorphism
  • sexes colored or patterned differently
  • male more colorful
  • Average mass
    43 g
    1.52 oz
  • Average length
    17.78 cm
    7.00 in
  • Average wingspan
    29.21 cm
    11.50 in

Reproduction

Polygyny has been observed in many grassland bird species, including bobolinks. Males may be able to mate with up to 4 females. Polygyny often occurs when food sources are available in the surrounding area and there is ample vegetation for protection. The first mated females are called “primary females”, while the second mated females are “secondary females”. Male bobolinks perform flight displays as advertisements, which correlate with their health and the number of offspring produced. Males that continue their displays the longest are usually preferred by females. Bobolinks may also engage in extra-pair fertilizations. In such cases, members of the same brood are sired by different males. Extra-pair fertilizations are most frequently committed by younger males and older females. (Bollinger and Gavin, 1991; Gill, 2007; Mather and Robertson, 1992; Semenchuck, 1992; Wittenberger, 1980)

Bobolinks return to breeding grounds in late April to early June, depending on their range. These birds often return to the same breeding sites each year, although they may select a new breeding area if their previous area is no longer optimal. Females build shallow cup nests made of grasses and other plant materials, generally on the ground in grassland areas. These birds typically have only one brood per year, with 3 to 7 splotchy, gray or cinnamon colored eggs. The eggs are incubated by the female for about 10 to 13 days. Nestlings fledge in about 10 to 14 days, but are not able to fly for several additional days, in that time; nestlings hide in the tall grass. (Dechant, et al., 2001; Engels, 1962; Gavin, 1991; Petersen and Meservey, 2003; Semenchuck, 1992)

  • Breeding interval
    Bobolinks breed once a year.
  • Breeding season
    Their reproductive season occurs from March to August.
  • Range eggs per season
    3 to 7
  • Average time to hatching
    12 days
  • Average fledging age
    1 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Due to weather conditions and food availability, time spent with nestlings is divided between male and female bobolinks. When food is scarce, males tend to brood less and feed nestlings more, while females maintain feeding rates and brood nestlings more when food is scarce and weather is unfavorable. However, females brood nestlings less and feed them more when weather conditions are favorable, to compensate for the food scarcity. Nestlings coincide with the hatching of primary nestling food sources, such as caterpillar hatching. Bobolinks feed their young for 10 to 13 days. They have a mean clutch size of 5 eggs; there is no significant difference in the clutch sizes of primary and secondary females. The average number of fledglings from a primary nest is 3.4, while the average number of fledglings from a secondary nest is 2.3. (Wittenberger, 1978; Wittenberger, 1982)

  • Parental Investment
  • male parental care
  • female parental care
  • pre-fertilization
    • protecting
      • male
      • female
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
  • pre-independence
    • provisioning
      • male
      • female

Lifespan/Longevity

Bobolinks often live 4 to 6 years and generally survive beyond 5 years. (Martin, 1973; Martin, 1974)

  • Range lifespan
    Status: wild
    2 to 9 years
  • Average lifespan
    Status: wild
    5 years

Behavior

As male bobolinks enter their breeding grounds, they quickly establish territories by song. Much of their behavior is linked to song. When attracting a mate, a male sings and shows off with aerial displays, to prove he has the best genes to ensure the next generation's survival. During nesting season, females often hide. If they are startled when they are near their nest, they often run through the grass, presumably to lead a predator away from their nestlings. Likewise, females do not land directly in their nests, but instead land several meters away and walk to their nest. Although these birds are territorial during nesting and breeding season, they are generally very gregarious and may be found in large flocks. During migration, bobolinks flock to roosting sites within one hour of dusk, particularly in areas near rice fields. Flocks include hundreds to thousands of individuals, which all depart about an hour from dawn. (Avery and Oring, 1977; Mather and Robertson, 1992; Petersen and Meservey, 2003; Renfrew and Saavedra, 2007; Semenchuck, 1992)

  • Range territory size
    4500 to 25,000 m^2

Home Range

Their territory size varies from habitat to habitat. In a mixed hayland, their territory can be from 0.45 to 0.69 ha, but it can increase to 2.5 ha in dry, sparsely vegetated pastures. (Dechant, et al., 2001)

Communication and Perception

Bobolinks produce songs that sound like a bubbly laugh that warbles with short notes on a wide pitch range. Their call is a soft "chuk" and their flight call is a musical "bink" or "bwink". Song variations are based on male-male and male-female interactions. Evidence suggests aggression or sexual motivation affects song switching and song frequency. Each male sings the same two stereotyped song types, known as alpha and beta songs; the alpha is about 7 seconds, while the beta is 4.5 seconds. Each song ends with a series of warbled notes. While the alpha begins with alpha introductory notes leading into a series of interior notes, the beta song begins with its own beta introductory notes. Males flutter in fields, singing their song and exhibiting flight pattern displays. Bobolinks are also extraordinary due to their long distance migrations. This is partially achieved by their ability to navigate magnetic fields, due in part to magnetite (iron oxide) present in their skulls. (Ammer and Capp, 1999; Avery and Oring, 1977; Capp and William, 1991; Capp, 1992; Gavin, 1991; Gill, 2007; Mather and Robertson, 1992; Sibley, 2003)

Food Habits

Feeding young depends on food availability and weather conditions. Male bobolinks spend most of their time at the primary females' (first mated) nests, as opposed to the secondary female's nests. The food delivered to nestlings consists of Lepidoptera, sawfly, and arctiid larvae, as well as mayflies. In May, male bobolinks gorge themselves on dandelion seeds and occasionally eat cutworms. By June, males begin eating cinquefoil seeds, yarrow, Canadian thistle, false lupine, dock, and mallow; habitat permitting. While migrating, bobolinks make extended pit stops to feed in rice fields. Bobolinks are diurnal foragers and have night-time roosts on their migration routes. Bobolinks are ground predators, foraging for insects and seeds. (Lawyer, 1918; Renfrew and Saavedra, 2007; Wittenberger, 1978; Wittenberger, 1980; Wittenberger, 1982)

  • Animal Foods
  • insects
  • Plant Foods
  • seeds, grains, and nuts

Predation

The rate at which nests are predated upon varies across their range. Predation rates are low in Oregon and high in Wisconsin. Likewise, nests located near the forest's edge, tend to have a high mortality rate. Nests are protected primarily by vegetation, consisting of tall grasses and shrubs. Along with other grassland birds, bobolinks' primary predators are other birds, snakes, and mammals. (Vickery, et al., 1992; Wittenberger, 1978; Wittenberger, 1980)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

Bobolinks influence insect populations within grassland ecosystems. They are also affected by the brood parasitism of brown-headed cowbirds. Bobolinks exhibit aggressive behavior towards female brown-headed cowbirds to prevent the brood parasitism. (Capinera, 2010; Robertson and Norman, 1976)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species

Economic Importance for Humans: Positive

Bobolinks are beneficial to farmers because they primarily consume insects while they care for their young. From May to August, when they are found in North America, their stomach contents are composed of 70 to 90% pest insects and 5% useful insects. Outside of the breeding season, bobolinks consume plant material. (Capinera, 2010; Dechant, et al., 2001)

  • Positive Impacts
  • controls pest population

Economic Importance for Humans: Negative

Bobolinks may consume rice from agricultural fields and may generally act as agricultural pests. (Lawyer, 1918)

  • Negative Impacts
  • crop pest

Conservation Status

Currently, bobolinks have a conservation status of 'least concern' according to the IUCN Red List of Threatened Species. This has changed over the past 100 years, as these birds were previously hunted in very large numbers due to their propensity for stealing crops; fortunately, this form of large scale hunting of bobolinks is generally no longer occurring. However, several threats exist for the species such as habitat destruction and climate change. Before European settlement, North America’s grasslands were vast (around 162 x 106 ha). The grasslands made up three regions: tallgrass prairie, shortgrass prairie, and mixed-grass prairie; which all but disappeared since European settlement, having been replaced with farms and croplands. The grasslands developed from natural fires and fires set by Native Americans. Bobolinks respond to the fires by inhabiting a site 2 years after a fire, prior to woodland growth. Habitat loss, fire prevention and development have impacted all grassland birds, leaving pockets of protected areas throughout North America. Climate change has also impacted bobolinks; global warming can cause major shifts in North American bird species, causing southern birds to replace bobolinks in parts of southern Minnesota. Grassland conservation benefits bobolinks and other fellow inhabitants. To protect the nesting grounds of grassland birds, a strategy of mowing half of large grasslands and leaving the other half idle has been proposed. This strategy encourages ecosystem diversity, depending on where the birds prefer to nest. (Azpiroz, et al., 2012; Brawn, et al., 2001; Gill, 2007; Horn and Koford, 2000; Petersen and Meservey, 2003)

Contributors

Amber Simon (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University, Leila Siciliano Martina (editor), Animal Diversity Web Staff.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

acoustic

uses sound to communicate

agricultural

living in landscapes dominated by human agriculture.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

insectivore

An animal that eats mainly insects or spiders.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

magnetic

(as perception channel keyword). This animal has a special ability to detect the Earth's magnetic fields.

male parental care

parental care is carried out by males

marsh

marshes are wetland areas often dominated by grasses and reeds.

migratory

makes seasonal movements between breeding and wintering grounds

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

visual

uses sight to communicate

References

Ammer, F., M. Capp. 1999. Song versatility and social context in the bobolink. The Condor, 101: 686-688.

Avery, M., L. Oring. 1977. Song dialects in the bobolink (Dolichonyx oryzivorus). The Condor, 79: 113-118.

Azpiroz, A., J. Isacch, R. Dias, A. Di Giacomo, C. Fontana, C. Palarea. 2012. Ecology and conservation of grassland birds in southeastern South America. Journal of Field Ornithology, 83: 217-246.

Bollinger, E., T. Gavin. 1991. Patterns of extra-pair fertilizations in bobolinks. Behavioral Ecology and Sociobiology, 29: 1-7.

Bollinger, E., P. Bollinger, T. Gavin. 1990. Effects of hay-cropping on eastern populations of the bobolink. Wildlife Society Bulletin, 18: 142-150.

Bollinger, E., T. Gavin. 2004. Responses of nesting bobolinks (Dolichonyx oryzivorus) to habitat edges. The Auk, 121: 767-776.

Brawn, J., S. Robinson, F. Thompson. 2001. The role of disturbance in the ecology and conservation of birds. Annual Review of Ecology and Systematics, 32: 251-276.

Capinera, J. 2010. Insects and Wildlife: Arthropods and Their Relationships with Wild Vertebrate Animals. UK: Chichester, UK: Wiley-Blackwell.

Capp, M. 1992. Tests of the function of the song repertoire in bobolinks. The Condor, 94: 468-479.

Capp, M., S. William. 1991. An experimental study of song type function in the bobolink (Dolichonyx oryzivorus). Behavioral Ecology and Sociobiology, 28: 179-186.

Chapman, F. 1890. On the changes of plumage in the bobolink (Dolichonyx oryzivorus). The Auk, 7: 120-124.

Dechant, J., M. Sondreal, D. Johnson, L. Igl, C. Goldade, A. Zimmerman, B. Euliss. 2001. Effects of management practices on grassland birds: bobolink. USGS Northern Prairie Wildlife Research Center, 124: 1-29.

Dunning, J., D. Scheiman, K. With. 2007. Metapopulation dynamics of bobolinks occupying agricultural grasslands in the Midwestern United States. The American Midland Naturalist, 158: 415.

Engels, W. 1962. Day-length and termination of photorefractoriness in the annual testicular cycle of the transequatorial migrant Dolichonyx (the bobolink). Biological Bulletin, 123: 94-104.

Gavin, T. 1984. Broodedness in bobolinks. The Auk, 101:1: 179-181.

Gavin, T. 1991. Why ask "why": The importance of evolutionary biology in wildlife science. Journal of Wildlife Management, 55:4: 760-766.

Gill, F. 2007. Ornithology, Third Edition. New York: W.H. Freeman.

Hamilton, W. 1962. Does the bobolink navigate?. The Wilson Bulletin, 74: 357-366.

Hamilton, W. 1962. Bobolink migratory pathways and their experimental analysis under night skies. The Auk, 79: 208-233.

Horn, D., R. Koford. 2000. Relation of grassland bird abundance to mowing of conservation reserve program fields in North Dakota. Wildlife Society Bulletin, 28: 653-659.

Lawyer, G. 1918. Federal Protection of Migratory Birds. Washington: Bureau of Biological Survey.

Loftin, H. 1958. Nature ramblings: The bobolink. The Science News-Letter, 73: 368.

Martin, S. 1974. Adaptations for polygynous breeding in the bobolink, Dolichonyx oryzivorus. American Zoologist, 14:1: 109-119.

Martin, S. 1973. Longevity surprise: The bobolink. Bird-Banding, 44: 57-58.

Mather, M., R. Robertson. 1992. Honest advertisement in flight displays of bobolinks (Dolichonyx oryzivorus). The Auk, 109: 869-873.

Perlut, N. 2011. A model for integrating wildlife science and agri-environmental policy in the conservation of declining species. Journal for Wildlife Management, 75: 1657-1663.

Petersen, W., W. Meservey. 2003. Massachusetts Breeding Bird Atlas. Amherst: Massachusetts Audubon.

Renfrew, R., A. Saavedra. 2007. Ecology and conservation of bobolinks (Dolichonyx oryzivorus) in rice production regions of Bolivia. Ornitologia Neotropical, 18: 61-73.

Robertson, R., N. Norman. 1976. Behavioral defenses to brood parasitism by potential hosts of the brown-headed cowbird. The Condor, 78: 166-173.

Semenchuck, G. 1992. The Atlas of Breeding Birds of Alberta. Alberta: Federation of Alberta Naturalists.

Sibley, D. 2003. Sibley Field Guide to Birds of Eastern North America. New York: Alfred A. Knopf.

Vickery, P., M. Hunter, J. Wells. 1992. Evidence of incidental nest predation and its effects on nests of threatened grassland birds. Oikos, 63: 281-288.

Wittenberger, J. 1980. Vegetation structure, food supply, and polygyny in bobolinks (Dolichonyx oryzivorus). Ecological Society of America, 61: 140-150.

Wittenberger, J. 1982. Factors affecting how male and female bobolinks apportion parental investments. The Condor, 84: 22-39.

Wittenberger, J. 1978. The breeding biology of an isolated bobolink population in Oregon. The Condor, 80: 355-371.

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