Nebraskans may be justifiably proud of our tallgrass prairies; few other states have a larger number of protected tallgrass prairies that are open to the public for our enjoyment and educational opportunities. They include prairies located in state parks, such as Rock Creek Station State Park in Jefferson County, and state wildlife management areas (WMAs), such as the 1,120-acre Pawnee WMA, Pawnee County, and 600 grassland acres in Twin Lakes WMA, Lancaster County. There are also some federally owned restored prairies, such as at Homestead National Monument in Gage County and Boyer Chute National Wildlife Refuge in Douglas County. City-owned prairies include both virgin and restored prairies in Lincoln’s Pioneers Park, and there are several Nature Conservancy prairies. The University of Nebraska owns the historically famous 240-acre Nine-Mile Prairie, located nine miles northwest of Lincoln. The best-preserved and one of the best-studied tallgrass prairies in Nebraska is National Audubon’s 800-acre Spring Creek Audubon Prairie. Located in the glacial moraine hills of southern Lancaster County, it was acquired by the National Audubon Society in 1999 and contains over 350 species of plants. A listing of more than 75 tallgrass prairies in eastern Nebraska, plus 13 more in adjacent states, is available online (Johnsgard, 2007). Most of these sites are freely open to the public.
The adjacent states of South Dakota, Iowa and Kansas also have many prairie preserves. In South Dakota, The Nature Conservancy owns about 10,000 acres of mostly tallgrass prairies at eight locations in eastern South Dakota, of which the 7,500-acre Samuel H. Ordway Jr. Memorial Preserve in the tallgrass–mixed-grass transition zone is the largest. Iowa’s few remaining tallgrass prairies are nearly all located in the loess hills region of western Iowa. The largest of these is the 3,000-acre Broken Kettle Grasslands near Sioux City, owned by The Nature Conservancy. In the Flint Hills region of eastern Kansas, the National Park Service and National Park Trust jointly manage the Tallgrass Prairie National Preserve, of 11,000 acres, and the 8,600-acre Konza Prairie is similarly jointly managed by The Nature Conservancy and Kansas State University.
Although dominated by a relatively few species of tall perennial grasses, tallgrass prairies are notable for the very large diversity of broad-leaved herbaceous plants that are also present, frequently comprising 300 or more species. Most of these plants, technically classified as “forbs,” fall into the general category of wildflowers, and it is the spectacular summer and fall array of native wildflowers that stimulates most people to visit prairies. For the discerning eye, not even the autumnal colors of our eastern deciduous forests can match the summer reds and pinks of prairie phloxes and roses, the later violet-purples of gayfeathers and coneflowers, the Indian summer yellows of goldenrods and sunflowers or the coppery tones of late autumn grasses. It is this diverse plant life, whose seeds, leaves and flowering parts support an interdependent population of insects and other invertebrates, that is the biological basis of the prairie’s native bird populations. Of the roughly 30 species of North American birds that are ecologically closely associated with grasslands, the largest single component is comprised of sparrows and other seedeaters, although even sparrows depend heavily on insects for proteins while feeding their young.
It is of interest to compare the species compositions of the grassland bird populations at Spring Creek Audubon Prairie and Konza Prairie, as both are relatively large grassland ecosystems with similar climates and vegetational attributes. Native species that breed in both locations and are particularly grassland-dependent are the greater prairie chicken, upland sandpiper, northern harrier, horned lark, field lark, grasshopper and Henslow’s sparrows, dickcissel, bobolink and the eastern and western meadowlarks. Other birds breeding in both prairies but having somewhat broader ecological niches are the northern bobwhite, American kestrel, killdeer, loggerhead shrike, cliff swallow, barn swallow, sedge wren, common yellowthroat, red-winged blackbird and brown-headed cowbird.
Prairie birds are something akin to prairie grasses; they are often confusingly similar and usually not very colorful. Yet what they might lack in color they often make up for in both song and behavior. Few Nebraskans would admit to not being touched by the spring songs of meadowlarks, whose clear voices by late February often proclaim the end of winter long before it is admitted by any of the people who accept the calendar’s insistence that spring always begins on the 21st of March.
Following the sometimes overly optimistic weather assessments of the meadowlarks, mid-March brings the next uniquely prairie concert—the dawn chorus of greater prairie chickens. Displaying from distant hilltops, as the grassy slopes are just being touched and illuminated by the rising sun, this rhythmic melody is so haunting and powerful as to make one almost believe in the presence of unseen spirits. It penetrates to some remote and perhaps ancestral part of the brain, producing a kind of restful mantra that makes one believe that all is well with the world, in spite of the overwhelming evidence to the contrary.
The complex mating choreographies of prairie chickens extend into and though April, by which time most of the other prairie birds will have arrived. Red-winged blackbirds begin to utter their familiar kong-kor-eee notes from nearby willow-lined wetlands, simultaneously exposing their blood-red wing-covert epaulets to capture the attention of any nearby female. Male bobolinks establish territories in wet meadows, periodically releasing a cascade of song as they launch into the air and patrol their self-proclaimed properties. Grasshopper sparrows and Henslow’s sparrows more quietly take up their territorial position in the previous year’s tall grasses, uttering soft, insect-like songs that, together with their camouflaged dead-grass plumages, perhaps help protect them from aerial predators.
One of the last of the major prairie songbirds to arrive is the dickcissel, which has to make a spring migration of more than a thousand miles from South America, where it winters from Colombia to French Guyana. Arriving in mid-May, the males in spring resemble a miniature meadowlark, with a yellow breast crossed by a black blaze, revealing their ancient blackbird-like evolutionary connections. Like the grasshopper and Henslow’s sparrows, dickcissels have declined greatly across North America as their prairie habitats have disappeared, but they maintain a tenacious hold in eastern Nebraska, where a combination of weedy old-field habitats, CRP grasslands and tallgrass prairie relict stands provide ideal habitats. The dickcissel is the most common prairie breeding songbird species at Konza Prairie in eastern Kansas, and the same is true in eastern Nebraska sites such as Spring Creek Prairie. The breeding range of the dickcissel fairly closely corresponds with the historic parts of the cowbird’s range, which once largely was associated with that of the bison but has since expanded to include much of the deforested pastures and croplands of North America.
Perhaps because of their great abundance, dickcissels are the favorite target of the brood-parasitic brown-headed cowbird in eastern Nebraska and are also prime victims at Konza Prairie. In Nebraska it is uncommon to find a dickcissel nest that does not have at least one cowbird egg among the host’s eggs. In a Kansas study John Zimmerman found that, among 544 nests, only 46 percent were unparasitized, while the remainder had up to as many as at least six cowbird eggs! Since a female cowbird will lay only one egg in each nest she parasitizes, the local cowbird population must be remarkably high in Kansas prairies, and the same appears to be true in Nebraska. In other Kansas grassland studies parasitism rates on dickcissels have been found to range from 50–91 percent of all nests found, as compared with 22–50 percent of grasshopper sparrow nests and 70 percent of eastern meadowlark nests.
In spite of the large number of eggs that they lay, cowbird reproduction is not very efficient. John Zimmerman reported that only 7 percent of 132 cowbird eggs in dickcissel nests resulted in fledged young, although other Kansas studies suggest that a more typical fledging success rate is about 23 percent. However, he also found that nonparasitized dickcissel nests produced an average of 3.7 fledged dickcissels per nest in prairie habitats, whereas among parasitized nests the dickcissels fledged only 1.8 of their own young per nest. In larger bird species, such as the red-winged blackbird, competition for food by nestlings is probably more evenly matched, but highly effective begging behavior by the cowbird chicks may allow them to grow faster and be more likely to fledge than their blackbird nestmates.
In contrast to more famous nest parasites like the famous Old World cuckoo, cowbirds have not evolved highly specialized traits, such as mimicking the host’s egg color and pattern or getting rid of the host young by pushing them or their eggs out of the nest, Instead, cowbirds rather indiscriminately drop their eggs into virtually every nest that they find, regardless of the host species. Some host species can recognize the alien egg and eject or otherwise eliminate it, while others simply accept it as one of their own.
In many songbird nests the young cowbirds often hatch slightly sooner than the host’s young and immediately begin to obtain much of the food brought by the parents, simply by their more prolonged and more insistent begging. Although a dickcissel brood might survive the presence of a single cowbird chick in the nest, every additional cowbird increases the chances that most or all the dickcissel young will starve to death before fledging. Only after late July, when the cowbirds finally stop laying eggs, do the dangers from them subside. It is likely that a single female cowbirds may lay 50 or more eggs in a single breeding season, and one female was proven to lay 67 eggs in as many days!
In spite of the massive damage cowbirds have brought to grassland and forest-edge bird populations, the overall range of cowbirds has now stabilized, and their national population density has been stable or declining slowly since the mid-1960s. Probably the present greatest current threat to prairie bird populations is the continuing loss of grassland habitats through ever more conversions to cropland. Grassland birds have many other enemies such as snakes weasels, and even ground squirrels, which devour eggs and chicks. Avian predators include great horned owls, taking larger species such as quails and prairie chickens, and fast-flying accipiters such as Cooper’s and sharp-shinned hawks, which concentrate on progressively smaller birds. Natural disasters such as wind, snow, rain and hailstorms all contribute to avian mortality, so that at times it seems impossible that any birds will survive. Yet year after year they appear on schedule, go through all the dangers and difficulties of life and annually provide us not only with the joys of seeing and hearing them but also offer models of parental care and devotion. Even cowbirds have to be respected for their remarkable adaptive capacities to survive and reproduce in an unforgiving world.
Johnsgard, Paul A. “Prairie Birds: Fragile Splendor in the Great Plains.” Lawrence, Kan.: Univ. Press of Kansas, 2001.
Johnsgard, Paul A. “A Guide to the Tallgrass Prairies of Eastern Nebraska.” Lincoln, Neb.: Paul A. Johnsgard, 2007.
Zimmerman, John L. “The Birds of Konza: The Avian Ecology of the Tallgrass Prairie.” Lawrence, Kan.: University Press of Kansas, 1993.
Image Credits: Paul A. Johnsgard