Lark Buntings are one of the most striking sparrows in North America with their contrasting plummage and have a very impressive song flight.
Lark Buntings are heavyset sparrows with a very large, conical bill, and a compact, robust body. The bill and overall shape are similar to a grosbeak or bunting. Breeding males are an unmistakable black with white wing patches. Nonbreeding males, as well as females and immatures, have brownish upperparts and pale with brown streaking in their underparts, with extensive white in the upperwing coverts and small white tips to the inner tail feathers. The bill is a distinctive pale blue-gray.
Lark Buntings are larger than a Song Sparrow and slightly smaller than a Fox Sparrow . They have a length of 5.5-7.1 inches (14-18 centimeters) and weigh 1.3-1.5 ounces (35.3-41.3 grams) with a wingspan of 9.8-11.0 inches (25-28 centimeters).
Lark Buntings are endemic to the grasslands and shrubsteppe of North America —they occur nowhere else. When breeding, they are most likely to be found in large areas of native grassland vegetation. Lark Buntings avoid bare ground when nesting (Horned Larks are often found there), preferring shortgrass and taller habitats. They usually nest at the base of a small shrub or cactus, so pure grassland is usually not suitable for breeding habitat. Habitats with too little grass or grass too short are not typically used. They are medium distant migrants, migrating from central North America (breeding grounds) to Mexico and southern U.S (wintering grounds). While wintering and migrating Lark Buntings usually occur in flocks, sometimes with other sparrows, in many types of open habitats. Most are observed in open lowland areas, but they have been seen at elevations in the Rockies as high as 12,900 feet during migration. Across large areas of their wintering range, abundant natural food is available chiefly where unpredictable summer rains have fallen. This unpredictability means that Lark Buntings wander during winter, and they frequently show up in human -modified habitats such as cattle feedlots and weedy roadside edges.
Like other sparrows, Lark Buntings feed on seeds, invertebrates, and some fruits. They likely eat more insects than seeds from spring through autumn since about two-thirds of the summer diet is composed of invertebrates. Their young are fed mostly insects. Foraging Lark Buntings take seeds while feeding on the ground or strip seeds from grasses and other plants, much in the manner of other sparrows. In pursuit of insects, Lark Buntings are agile and versatile predators, stalking, then chasing them down on foot, pursuing them in flight (females more so than males), and gleaning them from vegetation. One study found that females foraging on the ground moved more quickly than males.
The female selects the site for the nest, indicating her preference by scraping the site with her feet. The nests are built on the ground by both members of the pair. It is a loose cup formed of fine plant material. The nest’s upper rim is even with surrounding ground or just above it. Nests measure about 3.7 inches across, with the interior of the cup being 3 inches across and 1.5 inches deep. The height of the nest varies from about 1.5 to 3 inches.
Lark Buntings have one to two broods with two to five eggs in each per year. The eggs are an unmarked light blue with a length of 0.8-1.0 inches (2-2.5 centimeters) and a width of 0.6-0.7 inches (1.5-1.8 centimeters). Incubation period 10-12 days and nesting period is 7-9 days. At hatching, hatchlings are helpless with sparse gray down.
Male Lark Buntings sing in flight or from a tall perch. Singing males are most evident in flight as they ascend rapidly, then glide earthward, with most of the song given as they slowly descend.
Males arrive on the breeding grounds earlier than females and begin to establish territories where suitable nesting sites (shade-providing plants) are plentiful. At this time, before the arrival of the females, males frequently deliver a flight-song containing more pauses and harsh notes than the song they give later in the season. This different song seems to indicate aggression toward other males, as the males establish individual territories. Males that clash early in the nesting season also communicate aggression by flicking their wings, ruffling the feathers, or contorting the body. Because the birds’ territories are relatively small and thus close together, some observers have assumed that Lark Buntings are colonial nesters that don’t hold individual territories, but this is not true. Females also show aggression toward other females that enter their territory, and in a few cases, observers have seen Lark Buntings chase sparrows that approached the nest too closely. Once young hatch, the parents forage away from the territory.
After breeding, Lark Buntings gather into flocks that migrate, both day and night, southward toward wintering areas.
In spring and summer, males sing two different songs, both composed of repeated notes, given either slowly and distinctly or more rapidly, as trills. Songs are delivered in distinct phrases and can last up to 8 seconds. When the males arrive on the breeding territory, ahead of the females, they tend to sing an “aggressive flight song,” marked by harsher notes and pauses between phrases. As males establish territories and pairs form, males switch to singing a sweeter, faster song, from a perch or in flight.
The most common call note, often given by birds in flight, is a distinctive, gentle hweee, given by both males and females. Parents returning to the nest give a chittering call and while feeding their young they give a whert call. Begging young sometimes give an insectlike buzzy call.
Lark Buntings are common, but their numbers are facing a steep decline. This decline may be due changes in their habitats caused by humans.
- The Lark Buntings' song flight is similar to some Eurasian lark species (especially the Eurasian Skylark), and is the reason the buntings have "lark" in their common name, despite being unrelated taxonomically.
- Lark Buntings have interesting domestic arrangements. Pairs often nest close to one another in a loose “colony,” much as Dickcissels do. Most are monogamous, but some males breed with multiple partners (a mating system known as polygyny). In other areas, when males outnumber females, unmated males seem to serve as “nest helpers,” bringing food to young at the nest.
- Lark Buntings sing from a perch or in a flight display, and they appear to be unique among birds in having two different flight-song types.
- These birds may be able to survive periods of drought without drinking water, taking moisture from grasshoppers and other insects, their chief food during summer.
- The oldest recorded Lark Bunting was a male, and was at least 4 years and 10 months old when he was found in Arizona, the same state where he had been banded.
- Lark Butnings are also called Chingolo Albinegro (in Spanish) and Bruant noir et blanc (in French).