Ammodramus henslowii

Geographic Range

Henslow's sparrows are native to North America. They migrate between winter and summer ranges in the southeastern United States and southeastern Canada. Most begin their northern migration to breeding grounds in early March from the wintering grounds in the mid-Atlantic and Gulf coast states around Florida and Texas and reach the northern limits of their range in New England, southern Ontario, and eastern South Dakota by mid-May. They are rarely seen during their return trip to the south during fall migration (July to late October). Prior to European settlement, Henslow's sparrows are suspected to have lived and bred primarily in prairie habitats. The total global breeding range is approximately 1,100,000 km2. Henslow's sparrows have adapted to live and breed in secondary grassland habitats such as hayfields and pastures due to the loss of native prairie (largely to agriculture). The loss of native habitat and availability of these secondary habitats has caused the species range to expand north and to the east over time.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Henslow's sparrows prefer uncultivated grasslands or old fields with stalks for singing perches (ranging from 30 to 61 cm off the ground) and a substantial litter layer to nest in. Well-established litter depth, vegetation height (tall, dense grass), and number of standing dead herbaceous stems are important components of chosen areas. They prefer to settle in grasslands over 100 ha (247 ac.), but smaller areas of habitat can be used by this species. They are found in open fields and meadows with grass interspersed with weeds, un-mowed hayfields, or shrubby vegetation are often used, especially in damp or low lying areas adjacent to salt marshes. They are not typically associated with overgrazed areas, though they can survive quite well in pastures that are only lightly or moderately grazed.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

• Wetlands
• marsh marsh

• Other Habitat Features
• agricultural agricultural
• estuarine estuarine

Physical Description

Henslow’s sparrows belong to a relatively small genus (6 to 20 species). They are among the smallest of sparrows, noted for being a shy bird with a quiet, short, two-syllable song. They range in size from 11 to 13 cm, weighing an average of 13 g, with an average wingspan of 20 cm. The most distinctive feature is their large, relatively flat, olive-colored head with dark stripes. They have streaked chests, reddish-brown tinged wings and short tails, with no sexual dimorphism. Juveniles are clay colored and streaked with black on the back and head. Due to their timid nature, Henslow’s sparrows are more likely to be heard than seen. When disturbed, they will often run instead of fly; in flight, they fly low and quickly over the grass in a drooping, zigzag fashion.

There are two subspecies of Henslow's sparrow recognized by the American Ornithologists Union: the western subspecies ( Ammodramus henslowii henslowii ) breeds throughout the species' entire range, while the eastern subspecies ( Ammodramus henslowii susurrans ) occurs only along the Atlantic coast. Some researchers suggest that this second subspecies is now extinct or virtually extinct.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Reproduction

Henslow's sparrows are socially monogamous after courtship occurs. Courtship includes a "call of intimacy," wing fluttering, and an evaluation of potential nest sites. Males return to breeding areas each spring and establish and defend territories through song. Most Henslow's sparrows establish their territories by singing from dead woody vegetation less than 1 m tall. Individual territories average 0.8 acres. Females almost exclusively build the nests; these are cup shaped or domed, made of coarse grass and dead leaves, and lined with finer grasses and sometimes hair. Nests are always well concealed and placed near or on the ground located above the base of a dense clump of grass. They are usually attached to stems that lean over the nest, creating a partial roof for protection.

• Mating System
• monogamous monogamous
• cooperative breeder cooperative breeder

Females typically begin building nests in early May with nests built 1 to 3 inches above the ground, at or near the base of a thick clump of grass. Henslow's sparrows often raise 2 broods of young per year. First clutches are normally completed by mid to late May and second nests are frequently initiated in July or August. Both sexes are presumed to breed at one year of age and they are socially monogamous. Females lay 3 to 5 eggs which are incubated for approximately 10 to 11 days. Young fledge 9 to 10 days after hatching. Both male and female parents feed and brood the young while they are in the nest and for a period after they leave it. In a study done in Maryland, five banded adult males exhibited site fidelity by returning to a prior year's breeding area, which suggests that home ranges may be stable.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• fertilization fertilization
• oviparous oviparous

Henslow's sparrows eggs are incubated by the female only. The incubation period begins with the last egg laid and lasts approximately 11 days. The young remain in the nest 9-10 days after hatching. The young are born in a relatively underdeveloped state and are unable to feed, care for themselves or move independently for a short period of time after hatching. Females are largely responsible for their young during all periods of development, with increased involvement from males after hatching. Their diet consists mainly of butterfly larvae, grasshoppers, and other insects.

• Parental Investment
• altricial altricial
• male parental care male parental care
• female parental care female parental care
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • male
    • female
• pre-weaning/fledging
  • provisioning
    • male
    • female
  • protecting
    • male
    • female
• pre-independence
  • provisioning
    • male
    • female
  • protecting
    • male
    • female

Lifespan/Longevity

The lifespan of Henslow's sparrows is short, with a generation time ranging from 2 to 3 years age and an average longevity of 6.5 years.

Behavior

Henslow's sparrows are social birds, living in solitary loose flocks. These flocks may combine where more suitable habitat or resources are found. They are not strictly colonial as the term is applied to herons, gulls, terns, or swallows. When migrating or wintering, Henslow's sparrows are usually found in small groups or alone. This species is diurnal and migratory. Henslow's sparrows have individual songs and often sing as a chorus or in dispute over territory. Males show territorial dominance through a two syllable song. Henslow's sparrows are non-territorial during the winter and it is unknown if they exhibit site fidelity during this season. Henslow's sparrows forage on or near the ground. This species has the habit of dropping to the ground and running, rather than flying, when flushed from its nest or covering. The flight pattern of Henslow’s sparrows has been described as erratic, rising and falling with a characteristic twisting of the tail just after beginning flight. When flushed they frequently fly only a little way before again dropping to the ground and running.

• Key Behaviors
• terricolous
• flies
• diurnal diurnal
• motile motile
• migratory migratory
• solitary solitary
• territorial territorial
• social social

Home Range

In many parts of their range, populations are somewhat unstable and have tended to decrease each year. It has been reported that habitat area and fragmentation are the most important factors influencing population (Henslow's sparrows are rarely encountered in grasslands less than 250 acres in size). Individual territory sizes vary but are on average 0.8 acres (3237.4 m^2), though boundaries are not well defined. Some studies report that most of the territories from southwestern Michigan to Madison, Wisconsin range from 0.75 acres to 1.21 acres.

Communication and Perception

Henslow’s sparrows use vocalizations and body language to communicate. They sing individually (to attract a mate), as a chorus, and to settle territorial disputes. They have a wide variety of calls used in different situations including predator alarm calls, courtship calls and calls of young in nests. The most often heard call is the two syllable "zee-lick", described by some as sounding like an insect. Nestlings can give off a faint chirp while begging for food. Henslow's sparrows use a variety of wing fluttering movements to communicate.

• Communication Channels
• visual visual
• acoustic acoustic

• Other Communication Modes
• duets duets
• choruses choruses

• Perception Channels
• visual visual
• tactile tactile
• acoustic acoustic
• chemical chemical
• magnetic magnetic

Food Habits

Henslow’s sparrows eat caterpillars, crickets, grasshoppers, beetles, spiders, and the seeds of herbaceous plants that they forage for on the ground. Studies have shown fledglings' diets to consist of about 80% grasshoppers and butterfly larvae. Adult sparrow diets have been reported to be approximately 36% crickets and short-horned grasshoppers, 19% beetles and 18% plant matter, with spiders, butterfly larvae, and bees making up the remainder of the food intake.

• Primary Diet
• carnivore carnivore
  • insectivore insectivore
  • vermivore
• herbivore herbivore
  • granivore granivore
• omnivore omnivore

• Animal Foods
• insects
• terrestrial non-insect arthropods
• terrestrial worms

• Plant Foods
• seeds, grains, and nuts

Predation

Humans present a great threat to Henslow's sparrow populations through fragmentation of territory and agriculture. Snakes such as blue racers are known predators of this species. There are a few reports of nest parasitism by brown-headed cowbirds but the level of parasitism is relatively low (as Henslow's sparrow coevolved with brown-headed cowbirds, it is likely that the sparrow has become adapted to resist nest parasitism from this species). Thirteen-lined ground squirrels are documented predators of young Henslow's sparrows, as are feral cats. Investigators have documented increased nest predation with proximity of grassland to woody cover.

Ecosystem Roles

There are few reports of nest parasitism by brown-headed cowbirds; this may be because Henslow's sparrows coevolved with brown-headed cowbirds and the sparrows have become adapted to cowbird parasitism. However, rejection of cowbird eggs or other potential behaviors to minimize the impacts of cowbird parasitism have not been observed in Henslow's sparrow. Henslow's sparrows are also hosts to a number of parasites, including red mites and lice.

• Ecosystem Impact
• disperses seeds
• creates habitat

Economic Importance for Humans: Positive

There is a potential use for Henslow's sparrows as an indicator species for the health and productivity of large grassland habitats within the species' range, as well as for the health of groundcover in mature longleaf pine forests and other area. The grassland ecosystems on which it depends are among the most endangered ecosystems in North America and a combined use of management practices for grassland-dependent species and the grasslands themselves is a sound ecological approach, making the most efficient use of fiscal and scientific resources.

• Positive Impacts
• research and education

Economic Importance for Humans: Negative

There are no known adverse effects of Henslow's sparrows on humans.

Conservation Status

The current population of Henlow's sparrows is estimated to be 79,000 individuals. This species is observed within the North American Breeding Bird Survey and Christmas Bird Count to help with conservation efforts. It is listed as an Endangered species in Canada and seven states in its U.S. breeding range, as Threatened in five other states, and of Special Concern in four states. Populations have declined over the last three decades, with the greatest declines being in the northern and eastern portions of the range. Southern populations have increased slightly, likely due to the creation of undisturbed grassland habitat by the Conservation Reserve Program. Creation of large areas of undisturbed grasslands through this program appears to have been responsible for recent reversal of long-term population declines but this species is still in dire need of attention.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Scott Thorson (author), Minnesota State University, Mankato, Robert Sorensen (editor), Minnesota State University, Mankato, Jeremy Wright (editor), University of Michigan-Ann Arbor, Catherine Kent (editor), Special Projects.

References

Alderfer, J. 2006. National Geographic complete birds of North America . Washington, D.C.: National Geographic.

Burhans, D. 2002. Conservation Assessment--Henlow's Sparrow Ammodramus henslowii . General Technical Report , NC-222: 1-46. Accessed August 13, 2012 at http://nrs.fs.fed.us/pubs/gtr/gtr_nc226.pdf .

DNR, 2012. "Ammodramus henslowii" (On-line). Accessed February 08, 2012 at http://www.dnr.state.mn.us/rsg/profile.html?action=elementDetail&selectedElement=ABPBXA0030 .

Hanson, L. 1994. The Henslow's Sparrow of Minnesota: Population Status and Breeding Habitat Analysis . Mount Pleasant, Michigan: Central Michigan University.

Herkert, J. 2003. "Northern Prairie Wildlife Research Center" (On-line). Effects of management practices on grassland birds: Henslow's Sparrow. Accessed April 01, 2012 at http://www.npwrc.usgs.gov/resource/literatr/grasbird/hesp/hesp.htm .

Herkert, J. 2007. Evidence for a Recent Henslow's Sparrow Population Increase in Illinois. The Journal of Wildlife Management , Vol. 71, No. 4: 1229-1233.

Pearson, G. 1936. Birds of America . Garden City, N.Y.: Garden City publishing company, inc.,.

Robins, J. 1971. A Study of Henslow's Sparrow in Michigan. The Wilson Bulletin , Vol. 83, No. 1: 39-48.

Committe on the Status of Endangered Wildlife in Canada. COSEWIC assesssment and status report on the Henslow's Sparrow Ammodramus henslowii in Canada. x + 37 pp. Ottawa: COSEWIC. 2011. Accessed April 01, 2012 at www.sararegistry/.gc.ca/status_e.cfm .

U.S. Department of Agriculture, Forest Service. Conservation assessment: Henslow’s Sparrow. Gen. Tech. Rep. NC-226.. North Central: U.S. Department of Agriculture, Forest Service. 2002.

U.S. Fish and Wildlife Service. Henslow's Sparrow status assessment. -. Bloomington, Indiana: U.S. Fish and Wildlife Service. 1996.