It should come as no surprise to learn that the most characteristic birds of the Great Plains are small, mostly dead-grass brownish, and inconspicuous; there are few places to hide or nest in grasslands except among the grasses themselves. Of all of the native terrestrial birds in North America north of Mexico, less than 10 percent, or about thirty species, can be considered as Great Plains endemics. This term describes those species that are not only native to a geographic or ecologic region but are also essentially limited to it.
The 200-plus species of birds that breed within the Great Plains are of special interest for several reasons. First, there are those relatively few grassland endemics that presumably evolved in a semiarid grass-dominated environment and consequently have acquired an array of ecologically adaptive characteristics (ground-nesting, often seed-eating, with well-camouflaged plumages). They also have communication systems (vocalizations and plumage patterns) that are adaptively modified for effectiveness in openfield environments, such as singing in flight rather than from elevated perches. Many have conspicuous wing, tail, or underpart markings that are highly visible while flying but are hidden when on the ground. A dozen species of sparrows, five shorebirds, three grouse species, two meadowlarks, the horned lark (Eremophila alpestris), and the Sprague's pipit (Anthus spraguei) all closely conform to this combination of traits. A half-dozen predatory birds, which are often open-country species that may also range into deserts, also are grassland adapted. These include the prairie falcon (Falco mexicanus), Swainson's and ferruginous hawks (Buteo swainsoni and B. regalis), northern harrier (Circus cyaneus), and the short-eared and burrowing owls (Asio flammea and Athene cunicularia), although a few of these are tree- or cliff-nesters rather than being strictly groundnesting. Finally, three aquatic species that are adapted to nesting in prairie marshes, the Wilson's phalarope (Phalaropus tricolor), black tern (Chlidonias niger), and Franklin's gull (Larus pipixican), round out the list of Great Plains endemics.
The second group of birds having particular relevance to the Great Plains are those closely related species occurring in forests both to the east and west of the Plains, but that are largely excluded from the Plains grasslands. These often penetrate and locally cross the Plains only along those predominately east.west river systems supporting su.cient woody growth that provide narrow corridors for the birds to exploit. In many respects these species are of even greater biological interest than are the strictly grassland endemics, because where the western species encounter the eastern near-relatives, interactions can occur between them for the first time since their ancestors were originally separated. This may have happened as long ago as when the Great Plains grasslands originally developed as mountain building to the west produced increasing aridity eastwardly, or at least since the last glaciations had similar isolating effects on the Northern Plains. It is in such ecological and genetic "suture zones," such as those provided by the Platte and Niobrara River valleys in Nebraska, that these populations come into contact and variably interact. Examples of such eastern versus western relatives include the Baltimore and Bullock's orioles (Icterus galbula and I. spurius), the rose-breasted and black-headed grosbeaks (Pheuticus ludovicianus and P. melanocephalus), the indigo and lazuli buntings (Passerina cyanea and P. amoena), and the eastern and spotted towhees (Pipilo erythropthalmus and P. maculatus). All of these closely related pairs meet and, to varying degrees, hybridize along river corridors. The extent to which such hybridization results provides a rough index to their genetic disparity and the duration of separation of their populations. The most extensively hybridizing species pairs among the birds mentioned are the towhees and the orioles, which have broad and extensive zones of hybridization and have until recently been considered as subspecies. However, the grosbeaks and buntings show reduced levels of hybridization and their species distinctiveness has rarely been questioned. Yet because of increased degrees of tree planting across the Plains and the progressive growth of riverine forests since the cessation of prairie fires, the frequency of hybridization opportunities for such species pairs may continue to increase.
A third group of birds that nest at least in parts of the Great Plains are other woodland birds that do not necessarily have eastern and western counterparts. Many of these are of nearly universal occurrence throughout the forests of North America and have managed to penetrate the limits of the Great Plains in various regions. Surprisingly, these treeadapted birds comprise about half of the total Plains avifauna, even though woodlands and forests occupy less than 5 percent of the total area of the region. These birds include groups such as woodpeckers, warblers, vireos, and other mostly insect-eating and tree-foraging or tree-nesting birds.
Although no Great Plains birds have become extinct, many grassland-adapted birds have undergone severe population declines in recent years as native grasslands have disappeared. In an analysis of breeding bird populations based on annual surveys done between 1966 and 1993, only four of twenty-eight monitored grassland species have shown positive, statistically significant population trends. Twenty-one species have exhibited population declines, many of them statistically significant.
Paul A. Johnsgard University of Nebraska-Lincoln
Johnsgard, Paul A. Birds of the Great Plains: Breeding Species and Their Distribution. Lincoln: University of Nebraska Press, 1979.
Johnsgard, Paul A. The Nature of Nebraska: Biodiversity and Ecology. Lincoln: University of Nebraska Press, 2001.
Johnsgard, Paul A. Prairie Birds: Fragile Splendor on the Great Plains. Lawrence: University Press of Kansas, 2001.