Studies in Avian Biology No. 15:247-257, 1994. A VI AN ASSEMBLAGES ON ALTERED GRASSLANDS FRITZ L. KNOPF Abstract. Grasslands comprise 17% ofthe North American landscape but provide primary habitat for only 5% of native bird species. On the Great Plains, grasslands include an eastern component of tall grasses and a western component of short grasses, both of which have been regionally altered by removing native grazers, plowing sod, draining wetlands, and encouraging woody vegetation. As a group, populations of endemic bird species ofthe grasslands have declined more than others (including neotropical migrants) in the last quarter century. Individually, populations of the Upland Sandpiper and McCown's Longspur have increased; the wetlands-associated Marbled Godwit and Wilson's Phalarope appear stable; breeding ranges are shifting for the Ferruginous Hawk, Mississippi Kite, Short-eared Owl, Upland Sandpiper, Horned Lark, Vesper, Savannah, and Henslow's sparrows, and Western Meadowlark; breeding habitats are disappearing locally for Franklin's Gull, Dickcissel, Hens­ low's and Grasshopper sparrows, Lark Bunting, and Eastern Meadowlark; and populations are declining throughout the breeding ranges for Mountain Plover, and Cassin's and Clay-colored sparrows. Declines of these latter three species, and also the Franklin's Gull, presumably are due to ecological phenomena on their respective wintering areas. Unlike forest species that winter in the neotropics, most birds that breed in the North American grasslands also winter on the continent and problems driving declines in grassland species are associated almost entirely with North American processes. Contemporary programs and initiatives hold promise for the conservation of breeding habitats for these birds. Ecological ignorance of wintering habits and habitats clouds the future of the endemic birds of grass­ lands, especially those currently experiencing widespread declines across breeding locales. Key Words: Grasslands; Great Plains; biological diversity; Larus pipixcan; Charadrius montanus; Aimophila cassinii; Calamospiza melanocorys. Native grasslands represent the largest THE NATIVE GRASSLAND vegetative province of North America. Al­ LANDSCAPE most 1.5 x 10 6 km2 of grasslands histori­ cally covered the continent on the Great Inferences about the historical landscapes Plains from south central Saskatchewan to of the Great Plains are available in the writ­ central Texas, plus in the Central Valley of ings of nineteenth century adventurers as California and Palouse region of eastern Irving (1835), explorers as Fremont (1845) Washington and Oregon (Knopf 1988). The and Stansbury (1852), and civilian travelers continental grasslands of the Great Plains along the Platte River Road (Mattes 1988). evolved in the rainshadow of the Rocky Read collectively, one envisions the short Mountains; seasonal precipitation falls and taller grass prairies intergradingjust east mostly in spring or summer. These grass­ of an irregular line from EI Reno, Oklaho­ lands are characterized by warm-season ma, through Fort Hays, Kansas, and North grasses of the shortgrass prairie on the west Platte, Nebraska, northwestward into the and fire-maintained, cool- and warm-sea­ west-central Dakotas. The landscapes of son grasses that grow much taller on the eastern Oklahoma, Kansas, and Nebraska east. The mediterranean grasslands of the were heavily wooded stream bottoms in up­ west coast states evolved with fall/winter lands of fire-maintained grasses of a meter precipitation and the historical composition or more in height. Wapiti (Cervus canaden­ of especially the California grasses is un­ sis) and white-tailed deer (Odocoileus vir­ certain. This paper focuses specifically on giniana) were abundant. The grasses, how­ the Great Plains landscape and major pat­ ever, do not cure well (i.e., lose their nutritive terns of avifaunal metamorphosis over the value when dried) and these ungulates sur­ last 100 years. vived the season of vegetative dormancy by 247 248 STUDIES IN AVIAN BIOLOGY NO. 15 grazing or browsing within the wooded cal geographic features or vegetative asso­ stream bottoms. Native Americans of this ciations. region, such as the Pawnee, hunted these Although the Great Plains played a major species, but generally raised vegetables in role in the evolution of the North American relatively permanent villages along eastern avifauna (Mengel 1970), the grassland avi­ prairie streams then journeyed west into the fauna itself is relatively depauperate. Only shortgrass province semiannually to hunt 5% of all North American bird species are plains bison (Bison bison bison), for meat believed to have evolved within the Great (Hyde 1974). Plains (Udvardy 1958, Mengel 1970). Men­ The shortgrass prairie landscape was one gel (ibid.) listed 12 species of birds endemic of relatively treeless stream bottoms and to the grasslands along with 25 others that uplands dominated by blue grama (Boute­ he considered to be secondarily evolved to loua gracilis) and buffalo grass (Buchloe grasslands (Table 1). Two of the endemics dactyloides), two warm-season grasses that frequent wetland habitats within the grass­ flourish under intensive grazing pressure by lands, with the others being upland species. reproducing both sexually and by tillering. Species that are secondarily evolved to the Unlike the more eastern species, short grass grasslands typically occur in more wide­ species remain highly digestible and retain spread geographic areas and are found pri­ their protein content when dormant. This marily in landscapes where brush or trees character supported the evolution of a ma­ have invaded grasslands on the periphery jor herbivore assemblage dominated by bi­ of the Great Plains. None of the secondary son, pronghorn (Antilocapra americana) and species are wetland associates, although the prairie dogs (Cynomys spp.). Native Amer­ breeding biology of the White Pelican (Pele­ icans, including the Sioux and Cheyenne of canus erythrorhynchos) suggests that it also shortgrass landscapes, tended to be semi­ is a member of this more widespread group nomadic, following the massive bison herds (Knopf 1975). Five of the secondary species upon which their lifestyle was specifically (Sage Grouse, Sage Thrasher, Green-tailed dependent in the late 1870s. Towhee, Sage Sparrow, and Brewer's Spar­ row) are really species of the Great Basin THE NATIVE GRASSLAND BIRDS shrubsteppe. As is the case for most biogeographic The endemic birds evolved with specific provinces, pre-settlement information on ecological niches within the grasslands. native bird assemblages of Great Plains Wetland species obviously occur locally at grasslands is limited. Ornithological study moist-soil sites. Species of taller grasses as on the Great Plains commenced in 1832 the Greater Prairie-chicken and Dickcissel when John Kirk Townsend (1839, the first nest in habitats of standing residual vege­ trained zoologist to cross the continent) ac­ tation from a preceding growing season and companied by the prominent naturalist are dependent upon stand rejuvenation by Thomas Nuttall traveled with the Wyeth periodic fires (e.g., Kirsch 1974). Many of expedition along the Rocky Mountain Road the endemic species of shortgrass and mixed to the Columbia River. Later, the surveys grass landscapes such as the Baird's Spar­ by Hayden (1862), Allen (1871, 1874), row, McCown's and Chestnut-collared Coues (1878) and others provided addi­ longspurs coevolved with grazing ungulates, tional insights into the regional avifauna. whereas others such as the Ferruginous Generally, however, these earlier works were Hawk, Prairie Falcon, and Burrowing Owl all exploratory, tended to emphasize avi­ are strongly associated with prairie-dog faunas along stream courses (Allen 1874), towns. Evolutionarily, drought tolerance and provided few perspectives of avian spe­ appears to be the principal ecological pro­ cies densities or assemblages relative to 10- cess influencing grassland-bird assemblages BIRDS ON CHANGING GRASSLANDS-Knopf 249 locally (Wiens 1974), with grazing (Hobbs TABLE I. THE NORTH AMERICAN GRASSLANDS AVI­ and Huenneke 1992) and wildfire (Zim­ FAUNA (AFrER MENGEL 1970). merman 1992) having major, secondary Non-passerines Passerines roles. I. Primary species (endemic) THE CONTEMPORARY LANDSCAPE I. Buteo regalis Ferrugi- I. Anthus spragueii nous Hawk Sprague's Pipit The landscape of the Great Plains has un­ 2. Charadrius montanus 2. Aimophila cassinii Mountain Plover Cassin's Sparrow dergone significant alteration from descrip­ 3. Numenius american- 3. Ammodramus bairdii tions provided in early accounts. The im­ us Long-billed Curlew Baird's Sparrow pacts have been varied, with many (e.g., 4. Limosa fedoa Mar- 4. Calamospiza mela- bled Godwit nocorys Lark Bunting urbanization, mineral exploration, defense 5. Phalaropus tricolor 5. Calcarius mccownii installations) having primarily local im­ Wilson's Phalarope McCown's Longspur pacts on the native avifauna. Activities with 6. Larus pipixcan Frank- 6. C. ornatus Chestnut- lin's Gull collared Longspur more universal impacts on the landscape have included 1) transformation of the na­ II. Secondary species (more widespread) I. Ictinia mississippien- I. Eremophila alpestris tive grazing community, 2) cultivation of sis Mississippi Kite Horned Lark grains and tame grasses, 3) draining of wet­ 2. Buteo swainsoni 2. Oreoscoptes montan- lands, and 4) woody development in the Swainson's Hawk us Sage Thrasher 3. Circus cyaneus North- 3. Sturnella