Dolichonyx oryzivorus

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.

• Biogeographic Regions
• nearctic nearctic
  • native native
• neotropical neotropical
  • native native

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.

• Habitat Regions
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

• Aquatic Biomes
• lakes and ponds

• Wetlands
• marsh marsh

• Other Habitat Features
• agricultural agricultural

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.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes colored or patterned differently
• male more colorful

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.

• Mating System
• polygynous polygynous

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.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• oviparous oviparous

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.

• Parental Investment
• male parental care male parental care
• female 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.

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.

• Key Behaviors
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• territorial territorial

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.

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.

• Communication Channels
• visual visual
• acoustic acoustic

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• magnetic magnetic

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.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
• herbivore herbivore
  • granivore granivore
• omnivore omnivore

• 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.

• Anti-predator Adaptations
• cryptic 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.

• Ecosystem Impact
• disperses seeds

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.

• Positive Impacts
• controls pest population

Economic Importance for Humans: Negative

Bobolinks may consume rice from agricultural fields and may generally act as agricultural pests.

• 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.

Additional Links

Encyclopedia of Life

Contributors

Amber Simon (author), Northern Michigan University, Alec Lindsay (editor), Northern Michigan University, Leila Siciliano Martina (editor), Texas State University.

References

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