Grasshopper sparrow
The grasshopper sparrow 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, spiders, and seeds. Grasshopper sparrows are unusual among New World sparrows in that they sing two distinct song types, the prevalence of which varies with the nesting cycle. The primary male song, a high trill preceded by a stereotyped series of short chips, is reminiscent of the sounds of grasshoppers and is the origin of this species' name. Like some other birds of the central North American grasslands, this species also moves around a lot, not only via annual migrations, but individuals frequently disperse between breeding attempts or breeding seasons. Grasshopper sparrows are in steep decline across their range, even in the core of the breeding distribution in the tallgrass prairies of the central Great Plains. The Florida grasshopper sparrow is highly endangered.
Taxonomy
The grasshopper sparrow was described in 1713 by English parson and naturalist John Ray based on a specimen collected in Jamaica. It was described again and illustrated in 1725 by the naturalist and collector Hans Sloane. Both authors used the English name "Savanna bird". 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:A. s. perpallidus – southwest Canada and central, west USAA. s. ammolegus Oberholser, 1942 – south Arizona and northwest MexicoA. s. pratensis – southeast Canada and east USAA. s. floridanus – Florida A. s. bimaculatus Swainson, 1827 – central, south Mexico, Guatemala, Nicaragua and Costa RicaA. s. beatriceae Olson, 1980 – central PanamaA. s. cracens – north, east Guatemala, Belize, east Honduras and northeast NicaraguaA. s. caucae Chapman, 1912 – ColombiaA. s. savannarum – JamaicaA. s. intricatus Hartert, EJO, 1907 – HispaniolaA. s. borinquensis Peters, JL, 1917 – Puerto RicoA. s. caribaeus – Netherlands Antilles
Description
These small sparrows measure in length, span about across the wings and weigh from, with an average of. Adults have upper parts streaked with brown, grey, black and white; they have a light brown breast, a white belly and a short brown tail. Their face is light brown with a white eye ring and a dark brown crown with a central narrow light stripe. Adults sport bright yellow feathers at the crook of their underwing, and have a yellow-to-amber patch above their lores. Males and females cannot be distinguished by their plumage, and young birds molt into adult plumage within a few months of fledging.Distribution and habitat
Their breeding habitat is open fields and prairie grasslands across southern Canada, the United States, Mexico and Central America, the Caribbean. There is a small endangered population in the Andes of Colombia and Ecuador. In the central USA, birds are quick to locate newly available habitat, and can be attracted to sites by playing conspecific song. 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 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 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 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, consistent with birds completing their annual molt prior to migration. Individuals migrated an average of ~2,500 km over ~30 days. Birds migrate mostly over land, make few stop-overs of short duration, and travel at about 82 km/day. Data from the largely confirm the migratory patterns gleaned from prior work. 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 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. Data on first-year return rates is limited, but in NE Kansas, ~2% of young birds returned to the site to breed in the subsequent year.Grasshopper sparrows are unusual in their particularly high rates of breeding dispersal. Their high dispersal tendency may be due to the dynamic nature of the grassland environments on which they depend 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 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, and 20% returned in California. 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. Within-season breeding dispersal decisions relate to nest success; more birds moved following nest failure, and birds that dispersed experienced lower brood parasitism and higher nesting success following movements. 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.
Breeding
Grasshopper sparrows are a socially monogamous species, but rates of extra-pair mating can be high, and even instances of cooperative parenting have been documented. In the spring, males select and defend territories before being joined by a female. Over the course of the breeding season, birds can raise multiple broods, either with the same mate or a different mate. In the more southern regions of the species range, pairs may produce 2–4 broods while pairs further north are limited by shorter summers leading to 1–2 nesting attempts.Nest building
Females construct nests over the course of a couple of days. 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
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. Females incubate the eggs from 10 to 12 days, and nestlings fledge after 6–9 days. For the first few days of the nestling period, females primarily feed young, but both parents feed during the latter half of the nestling period. In one study, nonparental helpers were documented attending to broods and feeding young, but this behavior is apparently not ubiquitous. Nestlings are fed an arthropod rich diet, particularly prey ~15–40 mm long, and preferentially select acridid grasshoppers, spiders, and small beetles. 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.
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.
Causes of nest failure
Only 30–50% of nests successfully raise at least one or more nestlings that fledge the nest. The majority of grasshopper sparrow nests fail as the result of predation. 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.