Grasshopper sparrow

The grasshopper sparrow (Ammodramus savannarum) is a small New World sparrow. It belongs to the genus Ammodramus, which contains three species that inhabit grasslands and prairies. Grasshopper sparrows are sometimes found in crop fields and they will readily colonize reclaimed grassland. In the core of their range, grasshopper sparrows are dependent upon large areas of grassland where they avoid trees and shrubs. They seek out heterogenous patches of prairie that contain clumps of dead grass or other vegetation where they conceal their nest, and also contain barer ground where they forage for insects (especially grasshoppers), spiders, and seeds. When the German naturalist Johann Friedrich Gmelin revised and expanded Carl Linnaeus's Systema Naturae in 1789 he included the grasshopper sparrow. He placed it with the finches in the genus Fringilla, coined the binomial name Fringilla savannarum and cited the earlier authors. The grasshopper sparrow is now placed with two other American sparrows in the genus Ammodramus that was introduced by William Swainson in 1827.

Twelve subspecies are recognised: The spatial distribution of territories on the landscape can be clumped with several individuals defending territories near to one another interspersed by large areas of unused and apparently suitable habitat. The reasons for this clumping are elusive; aggregation is not related to group defense against predators or brood parasite, cooperative care, extra-pair matings, or kin selection. Appropriate habitat is strongly influenced by plant structure and precipitation amounts during previous seasons. Grasshopper sparrows avoid woody vegetation, and in the wetter parts of their range, prefer fields that are burned every 2–3 years (which reduces encroachment of trees and shrubs) and seek out areas that are moderately grazed by cattle or bison.

Behavior

Movement

Migration

Subspecies of grasshopper sparrows differ in their migratory behavior. The birds breeding in most of the eastern US and southern Canada (A. s. pratensis) migrate latitudinally up to several thousand kms each year, spending winters along the Gulf of Mexico and the Caribbean. The birds breeding through most of the Western part of their North American range (A. s. perpallidus) winter from Texas west to California, and south into the highland desert grasslands of northern and central Mexico. A. s. ammolegus, which breeds in the desert grasslands of SE Arizona, SW New Mexico, and adjoining states in northern Mexico, appears to be a short-distance, partial migrant, with some birds remaining resident year-round, and others likely moving further south in winter. Birds of multiple breeding populations and subspecies winter together in SE Arizona. Grasshopper sparrows breeding outside of North America, including those living in the Caribbean, Central America, as well as the Florida grasshopper sparrow are not known to migrate.

Males typically migrate north in the spring a week or two earlier than do females. Data from light level geolocators indicate that males are present on the breeding grounds from April to October, Individuals migrated an average of ~2,500 km over ~30 days. However, relatively few movement tracks for this species exist so far, potentially due to the sparrows' secretive behavior during most of the year other than the breeding season. Few recoveries of banded birds have ever been made, especially at sites other than a birds' initial banding location. In Oklahoma, grasshopper sparrows are one of the species most frequently found dead after colliding with windows, despite rarely being detected in migration.

Dispersal

In Maryland, a study of natal dispersal (the movement from a natal site to the site of first reproduction) revealed that most fledglings remained within their natal habitat during the summer months after fledging, and most recaptured fledglings were encountered within a couple hundred meters of their natal nests. Although distances recaptured from the nest increased with time, the average fledgling was recaptured only 346 meters from its nest and recaptured 33 days after fledging. The longest distance detected was 1.6 kilometers, which was accomplished in less than 20 days.

Grasshopper sparrows are unusual in their particularly high rates of breeding dispersal (i.e., one-way movements between successive breeding sites). Like some other grassland-dependent species, their dispersal movements lead them to be called semi-nomadic, as they opportunistically take advantage of suitable habitats as they appear on the landscape. Return rates of adult grasshopper sparrows to their previous breeding sites (site fidelity) differs widely between populations. Site fidelity is far higher in eastern parts of the breeding range, with >50% of adult males returning to breed in subsequent seasons at a site in Connecticut and over 70% in Maryland. In contrast, 0% of adult males in Nebraska returned to breed in subsequent years, 8.9% returned in Montana, In northeastern Kansas, individual birds also commonly disperse within seasons between nesting attempts. Between 30 and 75% of birds move over 100 m within season, and individuals were detected defending new territories or nesting up to 8.9 km from areas they occupied earlier in the season. Little is known about the movements of birds during winter, but inter-annual variation in abundance in northern Mexican grasslands is positively related to related to broad-scale variation in vegetation, rainfall the previous summer, and plant productivity. Grasshopper sparrows build inconspicuous, dome-shaped nests on the ground, typically very well hidden amongst grasses and forbs. The nests have a small side opening and are usually made of a mix of dead and live grasses. Nests are built on the breeding pair's territory in areas away from shrubs and trees.

Offspring

thumb|Nestling grasshopper sparrow within an hour or so of hatching (handled as part of permitted research) at the Konza Prairie, Kansas.

Females typically lay between 4–5 eggs per clutch. Grasshopper sparrow eggs are smooth and oval-shaped. They are a cream-white color, with reddish-brown speckling that is concentrated towards the larger end of the egg. and feeding young, but this behavior is apparently not ubiquitous. Upon leaving the nest, the offspring often remain in the area. Parents provide post-fledging care, but the duration and level of care is unknown.

thumb|Grasshopper sparrow nest with four cowbird eggs & one host egg

Brood parasitism

Grasshopper sparrows are a common host of the brown-headed cowbird, a brood parasite which lays their eggs in the nests of other species. Cowbirds can be detrimental to host species because they often remove host eggs and nestlings or destroy nests to initiate another nesting attempt, allowing for future parasitism. However, they do not necessarily reduce the chances of nests successfully fledging young. The rate of brood parasitism by brown-headed cowbirds varies across the grasshopper sparrow's range and depends on habitat characteristics such as the amount of woody vegetation and whether the land is grazed. In surveyed populations, 2–65% of nests were parasitized by cowbirds. Snakes, small mammals such as rats, larger mammals such as skunks, armadillos, hogs, and opossums, and even ants have been observed eating eggs and nestlings. Other causes of nest failure include flooding of the nest cup due to rainfall, trampling by livestock or humans, and abandonment by the parents.

In Florida, grasshopper sparrows may be eaten by some growth stage of invasive snakes such as Burmese pythons, Reticulated pythons, Southern African rock pythons, Central African rock pythons, boa constrictors, yellow anacondas, Bolivian anacondas, dark-spotted anacondas, and green anacondas.

Vocalizations

thumb|right|Grasshopper sparrow singing

thumb|right|Vocalizing, [[Suffield, CT]]

Primary song

The grasshopper sparrow's "primary" or "buzz" song has one to four introductory notes followed by a long high pitched trill,'tup zeeee' or 'tip tup zeee', and because of its similarity to a grasshopper sound, accounts for the name of the bird. There are small variations in the song between individuals, populations, and subspecies. The males will mainly use the primary song from mid-April, when they get to the breeding ground, to mid-August, when they are about to leave the breeding grounds. The song consists of a 5–15 second series of short notes varying slightly in pitch, and the entire sequence may be repeated two to four times. The leading cause of population decline across its range is linked to habitat loss and management, particularly conversion of grasslands to intensive agriculture and encroachment of shrubs and trees. Despite declining population sizes, grasshopper sparrows are classified as Least Concern by the IUCN and are also not included as a "Bird of Conservation Concern" by the U.S. Fish and Wildlife Services (USFWS) on a national level. The Florida grasshopper sparrow subspecies (Ammodramus savannarum floridanus) is classified as endangered by the USFW. This subspecies hit an all time population low of 15 breeding pairs in 2017, and reported a population of 120 in 2022.

Habitat management

The majority of the former breeding range of grasshopper sparrows in North America has been converted to intensive agriculture or encroached by shrubs and trees. Likewise, these birds are experiencing a loss of wintering habitats, particularly within the Chihuahuan grasslands, due to similar impacts (conversion to agriculture and woody encroachment). Because grasshopper sparrows require areas of dense dead grass for nesting, sparse vegetation for foraging, and little to no woody plants, they are vulnerable to management practices such as high-intensity grazing accompanied by annual burning, fire suppression leading to woody encroachment, and haying that can destroy nests if it occurs during the breeding season. Ideal grazing intensities and fire frequencies vary across their range depending on climate, but areas with moderate grazing by cattle or bison, prescribed burning every 2–3 years, and removal of woody plants tend to support the highest densities of grasshopper sparrows in the Southern great plains.

Gallery

File:Grasshopper Sparrow, Gerald R. Ford Int'l airport, 13 July 2014 (14691040876).jpg|Grasshopper sparrow

File:Grasshopper Sparrow Pawnee National Grasslands CO 2018-06-06 17-33-21 (40892558283).jpg|Grasshopper sparrow flying

File:Juvenile Grasshopper Sparrow in hand.jpg|Juvenile grasshopper sparrow

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References

External links

Grasshopper sparrow Species Account - Cornell Lab of Ornithology
Grasshopper sparrow - Ammodramus savannarum - USGS Patuxent Bird Identification InfoCenter

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Grasshopper sparrow

Behavior

Movement

Migration

Dispersal

Vocalizations

Primary song

Habitat management

Gallery

References

External links

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