Grasshopper Sparrow (Ammodramus savannarum)
he Grasshopper Sparrow (Ammodramus savannarum) belongs to the Order Passeriformes, Family Emberizidae. B irds of the genus Ammodramus are typically small to medium sized sparrows with relatively short tails that prefer grassy habitats. They are rarely seen in trees or bushes except when flushed and chased to a perch (some occasionally perch on wires). The species name savannarum describes the preferred habitat. The name “grasshopper” refers to the insect-like song.
A chunky sparrow with short narrow tail, large flat head, scaly-looking rufous upperparts, buffy breast and sides (adults usually without obvious streaking on underparts), dark crown with a pale central stripe, narrow white eye ring, and (in most adults) a yellow-orange spot in front of the eye; juveniles have pale buff breast and sides, finely streaked with brown,; average length 13 cm. In flight, orange feathers can be seen at the bend in the wings. Grasshopper Sparrows have a rather weak song. The primary song has been described as 1 or 2 high-pitched chip notes followed by a long, dry, grasshopper-like trill; while the sustained song is a more musical series of short buzzy notes.
BBS range map 1994-2003
resident of North America, the Grasshopper Sparrow breeding range extends from southern Canada to Central America, and across much of the United States. Grasshopper Sparrows winter from North Carolina to Florida, west to southern Arizona, and south to Mexico and Central America. Grasshopper Sparrows can be found throughout North Carolina, with the highest densities occurring in the western Piedmont.
Threats to Grasshoppers Sparrow populations include habitat fragmentation and loss due to cultivation, urban sprawl, and reforestation. Feral cats and edge predators are serious threats as well. Nests are impacted by early-season mowing of hayfields and intensive grazing practices. Grasshopper Sparrows belong to the “grassland” bird guild as well as the “ground-nesting” bird guild. Breeding Bird Survey (BBS) trends show that many species within these two guilds have been suffering population declines nationwide. The Grasshopper Sparrow in considered a species of conservation concern by North Carolina Partners in Flight and is listed on the North Carolina Natural Heritage Animal Watch List because of its known population decline and because of habitat threats. In recent years, BBS trends show steep population declines in the Piedmont of the eastern United States and a severe decline nationwide for this species. Grasshopper Sparrows are also on the U.S. Fish and Wildlife Service’s MNBMC List (Migratory Non-game Birds of Management Concern). The Florida Grasshopper Sparrow, a subspecies of the Grasshopper Sparrow, is on the United States Federal Endangered Species List.
Famously illusive, Grasshopper Sparrows dwell close to the ground and are most often detected by their buzzy insect-like song. Singing males can typically be found perched in a crouched position high on a grass stem, lone shrub, fence post, or power-line. When flushed, these sparrows will fly a short distance and drop out of sight into the grass. They feed largely on insects (primarily grasshoppers), but also on grass and forb seeds.
This species is extremely secretive when nesting. Nests are built by the female in a slight depression on the ground, typically well-hidden at the base of a grass clump, slightly domed on one side with vegetation arched over the top. If flushed from the nest, a Grasshopper Sparrow will sneak off the nest and run on the ground, looking much like a rodent, then fly up at least 20 feet away. The female may feign wing injury as a distraction. Females are known to sing and males sometimes sing at night during the breeding season.
Grasshopper Sparrows need large continuous open grassland habitat. In the East, this type of habitat rarely occurs naturally and is provided by abandoned weedy farm fields, hayfields, pastures, and to a lesser degree, airfields and grassy roadsides. Historically, natural prairies and savannas created by wildfire, grazing bison, and Native American disturbance may have provided the required habitat. Estimated area requirements range from 10 to 100 hectares (25-250 acres). Grasshopper Sparrows are found in various habitats ranging from low, sparse vegetation cover to tall dense cover. Grasses around 1 foot in height are preferred and these sparrows are often associated with clumped vegetation interspersed with patches of bare ground. Forbs are an important habitat component for attracting the insects on which they feed.
Grasshopper Sparrow (Ammodramus savannarum)
Nesting densities in cultivated cropland habitat are a fraction of the densities found in native grassland habitat. Nests are more successful the further they are from forest edge, indicating the need for large habitat patches.
Grasshopper Sparrows are highly sensitive to subtle changes in habitat and will easily abandon traditional nesting grounds if the grass grows too high and especially if woody plants begin to encroach. This species requires perches on the breeding grounds in order to defend territories. Grasshopper Sparrows are targeted in many conservation plans as an indicator species representing other grassland and area-sensitive bird populations. Grasshopper Sparrows tend to respond quickly to effective management and habitat restoration efforts.
Regardless of management treatment, avoid disturbing (e.g., burning, haying, heavy grazing) nesting habitat during the breeding season, approximately mid April to early August. Some management treatments may be performed 4 weeks prior to the arrival of adults from their wintering grounds (early April) or in the fall (early to late October). In fall, it is best to leave adjacent untreated areas to provide a place of refuge for fledglings or late or re-nesting adults.
Create and maintain large (over 25 acres) expanses of habitat. Grasshopper Sparrows are extremely area-sensitive and are not found on smaller grassland fragments. The smaller the acceptable habitat area, the lower the nesting success for these sparrows.
Create or maintain relatively sparse, grass dominated vegetation resembling old (8-10 years since planted) hayfields. Discourage woody vegetation. If mowing, grazing, or burning are not management options, hand cutting of woody plants may be required and an herbicide like Garlon may be used to control woody vegetation.
Defer mowing until the end of the breeding season. Studies have shown the number of Grasshopper Sparrow breeding pairs increase after several years of deferred mowing. Mow only 60% of the grassland at a time. Litter depth from mowing may take anywhere from 1 to 3 years to rebuild before another burn or mowing needs to take place.
Plant bunch grasses like Bluestems (Andropogon sp. or Schizachyrium sp.), Switchgrass, or Indian Grass that allow openings in vegetation to facilitate foraging and provide escape routes. Many bunch grasses are “warm-season” grasses that mature late in the summer and therefore do not need to be mowed until August, allowing for completion of nesting activities. These grasses are also very adaptable to drought conditions and provide good hay for cattle.
Prescribed burning may be used in place of mowing every 3 years, except during drought years. Drought reduces the above ground grass productivity to levels unacceptable to the sparrows. Burns should be performed during winter if it is determined they will be used in place of mowing. Studies have shown that Grasshopper Sparrows prefer areas 1-3 years after burning.
Avoid intensive grazing. Light to moderate grazing outside of the breeding season can be beneficial to Grasshopper Sparrows in lush grasslands or hayfields. Graze areas of tall dense vegetation to provide a diversity of grass heights and densities.
Treat portions of large areas on a rotational schedule to provide a mosaic of successional stages
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