Ammodramus henslowii (Audubon)
Rare to locally uncommon in winter, spring, and fall in Inland Coastal Plain and Gulf Coast regions. Occasional in fall, winter, and spring in Tennessee Valley and Mountain regions. HIGHEST CONSERVATION CONCERN.
A small (12-13 cm [4.75-5.25 in.] long) grassland sparrow with a relatively large, flat head and a large, pale bill. Striped olive-green head and reddish-brown wings are most distinctive field marks. Tail short, and back reddish-brown with dark streaks; breast and flanks buffy, with dark streaks. Usually only observed for brief glimpses as they flush from underfoot and fly low over vegetation for short distances with a distinctive twisting motion of the tail. Rarely vocalize during winter, but breeding males sing a feeble, hiccupping, tsi-lick, that is insect-like in quality. Two subspecies described (Graber 1968): The nominate or western subspecies (A. h. henslowii), occupies the largest geographic distribution, has a thinner bill, and generally is lighter in color with heavier streaks on the back. It is the race found wintering in Alabama. The Atlantic or eastern subspecies (A. h. susurrans) occupies a more restricted geographic distribution.
Breeds from eastern South Dakota to southern Ontario and northwestern New York southward to north-central North Carolina and northeastern Oklahoma. The Appalachian Mountains separate the distributions of the eastern and western subspecies. The eastern subspecies winters along the Atlantic Coastal Plain from South Carolina through south-central Florida. The western subspecies mostly winters along the Gulf Coastal Plain from eastern Texas to southeastern Georgia (Graber 1968).
Western subspecies breeds in grasslands that contain tall, dense grasses, a high percent coverage of standing dead vegetation, and relatively few shrubs (Zimmerman 1988). Occupied both native and non-native grasslands in Illinois, and size of grasslands appeared more important than vegetative composition; grasslands less than 100 hectares (247 acres) rarely occupied (Herkert 1994). Winters predominantly in open longleaf pine savannas, primarily coastal savannas and pitcher plant bogs (Plentovich et al. 1999). Habitats occupied during the breeding and nonbreeding seasons require frequent disturbances to maintain a dense herbaceous ground cover and to prevent encroachment of shrubs. Densities wintering on pitcher plant bogs in southern Alabama and northwestern Florida greatest the first winter after burning (Tucker and Robinson 2003). Although commonly found on bogs during the second winter after growing season fires, they were rarely found on bogs burned during winter except during the first winter post-burning. Productivity of grass seeds and density of forbs appeared to be most influential factors affecting presence on pitcher plant bogs (Tucker and Robinson 2003).
LIFE HISTORY AND ECOLOGY:
Although often stated to breed in “loose colonies,” males defend breeding territories and the species is not a colonial nester. Apparently monogamous; female builds nest on ground among layers of thick litter, or within large clumps of grass (Winter 1999). Both sexes brood and feed nestlings (Graber 1968). Clutch sizes range from three to five eggs, incubation lasts about 11 days, and nestlings fledge nine to 10 days post-hatching (Graber 1968). Few studies have examined breeding biology, but probably double-brooded (Winter 1999). Nesting extends from mid-May to mid-August; begin departing breeding grounds in September and most have departed by November (Graber 1968). Few data on food habitats published. During breeding season, diet apparently consists of mostly arthropods but seeds may predominate during fall and winter (Hyde 1939). Have a variety of mammalian, avian, and reptilian predators, but predation probably not a serious limiting factor. Nest predation and parasitism by brown-headed cowbirds appear relatively low. Information during winter even more limited than information during breeding season. Those wintering on pitcher plant bogs in Alabama exhibited strong site fidelity within, but not between, years (Plentovich et al. 1998). Although found on bogs more than 0.25 hectare (0.62 acre) about twice as frequently as on smaller bogs, about 25 percent of smaller bogs also were occupied, suggesting even small bogs are important (Tucker and Robinson 2003).
BASIS FOR STATUS CLASSIFICATION:
Data from the North American Breeding Bird Survey indicate Henslow’s sparrows have suffered among the most drastic population declines of any bird species in North America for more than 30 years. Although most of these declines can be attributed to loss of breeding habitat, loss of wintering habitat also may be a contributing factor (see review in Tucker and Robinson 2003). For example, more than 97 percent of GulfCoast pitcher plant bogs, a major wintering habitat, have been destroyed or severely altered (Folkerts 1982). Partners In Flight (PIF) assessment scores indicate the Henslow’s sparrow occurs in low relative abundance, has a very restricted nonbreeding distribution, and that severe deterioration in future suitability of nonbreeding conditions is expected (PIF 2002).
James W. Tucker, Jr.