Lark Bunting: The Unique Grassland Songbird of North America
The lark bunting (Calamospiza melanocorys) is a medium-sized American bunting native to the expansive grasslands of central and western North America. Known for its striking appearance and complex mating behaviors, this songbird holds a place of honor as the state bird of Colorado, a designation it has held since 1931.
Unlike many other songbirds, the lark bunting occupies a unique place in the avian family tree. It is a monotypic species, meaning it is the only member of its genus, Calamospiza, and is not closely related to any other genera.
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Key Facts
- Scientific Name: Calamospiza melanocorys
- Conservation Status: Least Concern (IUCN 3.1)
- State Bird: Colorado (since 1931)
- Primary Habitat: Prairies of central Canada and the mid-western United States
- Diet: Insects during summer; seeds during winter
- Unique Trait: Highly variable female mate preference that changes annually
Taxonomy and History
The lark bunting was first described in 1837 by J. K. Townsend as Fringilla bicolor following a trip with Thomas Nuttall. However, because that name was already in use for another species, Leonhard Hess Stejneger renamed it Calamospiza melanocorys in 1885. The genus Calamospiza had been established slightly earlier, in 1838, by Charles Lucien Bonaparte.
Physical Description
Lark buntings are small songbirds characterized by a short, thick, bluish bill. Their most distinguishing feature is a large white patch on the wings and a relatively short tail with white-tipped feathers.
Appearance varies significantly based on sex and season:
- Breeding Males: Feature an all-black body with a prominent white wing patch.
- Females and Nonbreeding Males: Display a more muted grayish-brown plumage with white stripes.
| Metric | Measurement (Imperial) | Measurement (Metric) |
|---|---|---|
| Length | 5.5–7.1 in | 140–180 mm |
| Weight | 1.3–1.5 oz | 37–43 g |
| Wingspan | 9.8–11.0 in | 250–280 mm |
Distribution and Habitat
The lark bunting is the most prevalent passerine (perching bird) species found in the North American grasslands. During the breeding season, they inhabit the prairie regions of the mid-western United States and central Canada.
As the seasons change, these birds migrate in large flocks to spend their winters in southern Texas, Arizona, and the high plateaus of northern Mexico.
Behavior and Breeding
Nesting and Courtship
Lark buntings typically nest in dispersed colonies, building open-cup nests directly on the ground in grassy areas. To establish territory, males fly high above their domain and sing a mixture of trills and whistles while descending. Their standard call is described as a soft "hoo."
Complex Mating Systems
While the species is socially monogamous, they engage in extensive extra-pair mating. This means that while a pair may maintain a social bond, paternity often comes from males outside that pair. This behavior is often linked to a male-biased breeding sex ratio, where many males are unable to find a social mate.
The Plasticity of Female Choice
One of the most fascinating aspects of the lark bunting is the plasticity (flexibility) of female mate choice. Unlike many species where a specific trait is always preferred, female lark buntings change their preferences from year to year. In any given year, they may favor males based on:
- The intensity of black coloring
- The size of the wing patch
- The size of the beak
- Overall body size and residual mass
This temporal flexibility prevents any single male trait from becoming overly exaggerated and helps maintain genetic variation within the population, similar to the natural selection patterns seen in Darwin's finches.
Diet and Foraging
Lark buntings are primarily ground-foragers. Their diet shifts with the seasons: they consume mainly insects during the summer and switch to seeds in the winter. While they mostly feed on the ground, they are known to take short flights to capture insects in mid-air. Outside of the nesting season, they are highly social and typically feed in flocks.
Conservation Status
The lark bunting is currently classified as Least Concern by the IUCN. However, there has been a noted decrease in their population due to the ongoing loss of their natural prairie habitats.
Frequently Asked Questions
What is the state bird of Colorado?
The lark bunting has been the official state bird of Colorado since 1931.
How can you tell a male lark bunting from a female?
During the breeding season, males are entirely black with a large white wing patch, while females and nonbreeding males are grayish-brown with white stripes.
What do lark buntings eat?
Their diet is seasonal; they primarily eat insects during the summer months and seeds during the winter.
Why is the mating behavior of the lark bunting unique?
They exhibit extreme variation in female mate choice, where the traits females prefer in males (such as beak size or color) change radically from one year to the next.
Where do lark buntings migrate for the winter?
They migrate in flocks to southern Texas, Arizona, and the high plateau regions of northern Mexico.