Studies Document Historic Avifauna of the Niobrara River Valley, Nebraska

By James Ed. Ducey. A condensed version of this was previously published: 1989. Birds of the Niobrara River Valley, Nebraska. Transactions of the Nebraska Academy of Sciences 17: 37-60. This version, prepared starting about 20 years ago and finished ca. 1988, has been only slightly edited and not updated.

The Niobrara River starts as a small narrow river in Wyoming and flows 487 linear miles (784 km.), through northern Nebraska, where the maximum east to west basin is 300 miles (482 km.) in length. The flora of the Niobrara Valley undergoes obvious transitions. Higher-elevation tablelands in the west are replaced by lower-elevation eroded tablelands in the east. Rough and rugged ridges, bluffs, and slopes in the central Valley are vastly different from the rolling, upland prairie further west. The woodlands of the Valley are a strong comparison with the dunes and swales of the adjacent Sand Hills. Near the Missouri River, towering cottonwoods are part of the floodplain forest. Wetlands abound along the entire channel area. In the western portion of the valley, a reservoir influences the occurrence of various species of birds.

The Niobrara River area has been recognized for many years for its unique setting and its influence on distribution of the avifauna. The Valley is an important site for the study of avian biogeography and hybridization. Many species found in the river woodlands have a range extended or disjunct from where they typically occur. Threatened and endangered birds use the Valley during migration or the breeding season.

There have been notable studies of birds in the Niobrara River. Some of the earliest notes were more than 150 years ago. When combined, these records provide an overall view of the Valley avifauna. This paper compiles the many different sources of information to present a summary of birdlife in the Niobrara Valley. For this paper, the Valley is limited to the river channel and its floodplain, and the canyons cut by the river and its tributaries up to the ridges along the deeply incised Valley. Extensive adjacent grasslands on the upland are excluded.

Bird Studies

Explorations on the Plains

The Niobrara River was an obvious landmark for explorers on their journeys along the Missouri River. Some expeditions happened to record their bird sightings for the area while others did not. But each observer noticed when the River was passed. The notes during the period of exploration of the Plains provide the first records of birdlife for the lower Niobrara.

Lewis and Clark Expedition

William Clark's entry for 4 September 1804, as he wrote it, read: "Came to at the mouth of the Qui courre (rapid) [based on the French name L'Eau qui Court which means the river that rushes] this river Comes roleing its Sands whuch (is corse) into the Missouris from the S W by W this river is 152 yards [139 meters (m)] across the water and not exceeding 4 feet [1.2 (m)] Deep Throwing out Sands like the Platt (only Corser) forming bars in its mouth it does not rise high when it Does it spreds over a large Surface, and is not navigable the river widens above its mouth and is devided by a great many Small islands & Sand bars, the Current verry rapid" (Moulton, 1983).

Wilhelm Expedition

Paul Wilhelm of Germany traveled in the eastern part of Nebraska in 1823 (Wilhelm, 1835). In the latter part of summer he went from Fort Atkinson on the Missouri to the mouth of the Niobrara. Birds seen in the area near the confluence of the two rivers included large flocks of ducks and geese, the greater prairie-chicken and what he said was a "grosbeak." There were no additional notes on birds, but Wilhelm mentioned several plants since he apparently was more interested in the flora than birds.

Expedition of Prince Maximilian of Wied

Prince Maximilian of Wied, Germany, made a journey up the Missouri River to study the features of the land. In addition to his many other studies, he kept extensive notes on birdlife. While traversing the Missouri on the steamboat Yellowstone, the expedition was in the Niobrara River area on 12 May 1833 and 5 and 6 May 1834. Despite Maximilian's usual flair for writing extensive descriptions of the sights seen during his travels, he simply wrote: "It is a pretty river." and said nothing more specific about the Niobrara River (Orr and Porter, 1983). I include seven species in this review because they were seen in the vicinity of the mouth of the river: American white pelican, passenger pigeon, cliff swallow, house wren, brown thrasher, yellow warbler, and rufous-sided towhee.

J.J. Audubon

The celebrated naturalist, John James Audubon, made a journey up the Missouri River in 1843. He made numerous observations of birds but none in the specific area of the Niobrara. He did however write: "the swift-flowing L'Eau qui Court, in some places is fully as broad as the Missouri itself, fully as muddy, filled with quicksands, and so remarkably shallow that in the autumn its navigation is very difficult indeed" (Audubon, 1960). No sightings were mentioned for the downriver trip either. Along with Audubon was his friend Edward Harris. Harris' journals mention that the Say's phoebe and western kingbird were shot or seen in this area on 21 May when they stopped to view the remnants of abandoned Fort Mitchell (McDermott, 1951).

The Warren Expedition

The Warren Expedition of the middle 1850's explored the Nebraska and Dakota Territories during reconnaissance for a travel route to the Black Hills. The main responsibility during this three-year exploration was to assess potential trails for horse-drawn wagons and to determine the best route to reach western outposts from a Missouri River depot. Wagon trains of supplies from Missouri River steamboats were to supply government posts such as Fort Laramie and the northern Great Plains in general (Warren, 1875).

An integral part of the expedition was a survey of the natural history of the region. F.V. Hayden, M.D. was the member of the party mainly responsible for preparing a catalogue of collections in geology and natural history prepared after the expedition was completed. There were many bird specimens collected during this time. These reveal what birds were present just prior to the time of the first settlers. The 1857 season was spent mostly in the region of the Nebraska territory. During this summer, two parties of the expedition met at the mouth of the Loup River to continue westward through the eastern Sand Hills and then north along the Niobrara River. They continued to Fort Laramie, through the Black Hills and returned to Fort Pierre via the Niobrara.

The observations made by the Warren expedition on the L'Eau Qui Court and Running Water, two historic names for the Niobrara, were included in two sources. The report from the Warren expedition presented the information but a second work done by Spencer Baird includes the dates when the specimens were collected (Baird, 1858). The dates provide information that helps determine the time of the observation to better determine status. Coues is the second source where specific specimen localities are given (Coues, 1875). The original Warren work was not used here because it was not specific about the locality where a species was noted.

Collection dates for pertinent expedition specimens are: 12 May 1856, May 1856, 15 August 1856, 20 October 1856 and 14 and 16 August 1857. Fourteen species were noted for the Running Water by this expedition: northern harrier, red-tailed hawk, greater prairie-chicken, burrowing owl, least flycatcher, cliff swallow, common raven, black-billed magpie, rock wren, brown thrasher, loggerhead shrike, rose-breasted grosbeak, chestnut-collared longspur and American goldfinch.

Other Historic Observations

In 1902, Robert H. Wolcott and other University of Nebraska personnel took a journey along 100 miles (160 km.) of the Niobrara River to examine and collect specimens (Ducey, 1983). The party left Long Pine on 14 June and proceeded downriver by boat until they reached the town of Niobrara on 9 August. They made a stop of two weeks at the Springview bridge and then a month at Carns to do more extensive studies in those areas.

In his manuscript, Wolcott (see Ducey, 1983) noted the changes in the vegetation along the river. He wrote:

"As we proceed eastward the character of the country gradually changes. The rugged surface outlines soften, the steep, shaly river banks caused by the eroded hills become less and less steep and finally melt away altogether, while the rough hills and canyons back from the river modulate into gentle undulations. When we reach the western border of Holt County the pines and cacti are left behind, the prairies begin to assume a greenish hue and an occasional cornfield in a moist Valley betokens the advent of farming land. After passing the northern bend and again turning to the south, the river country is predominated by eastern characteristics, until by the time we reach the Missouri we are on genuine prairie land.
"Even the character of the river itself changes, and from a broad, shallow stream studded with sandbars and dissipating its current in a myriad of little streamlets, it concentrates into a deep and narrow stream of great swiftness. The vegetation in the immediate vicinity of the river also undergoes a change, but more of a change in degree than in kind, for the narrow belt of cottonwood [Populus deltoides] and bur oaks [Quercus macrocarpa] broadens into timber of considerable size, while the underbrush of black [Salix nigra] and diamond willows [Salix eriocephala], buffalo berry [Shepherdia], choke cherry [Prunus virginiana], wild plum [Prunus americana] and similar thicket plants becomes denser.
"With the decided transition of conditions it is natural to expect a merging of eastern and western avifaunas and that is exactly what occurs."

A year later Dr. Wolcott and Frank Shoemaker made a visit to the lake district of east central Cherry County in the area of present day Valentine National Wildlife Refuge. Rivers Stilwell, the owner of the ranch where they were staying, used a light horse-drawn wagon to take them for a three day trip from 1-3 June. They went through Schlagel Creek Canyon and then along the Niobrara to Valentine. Shoemaker's notes give the species he noted in each area traversed. They took a side trip apparently to the river northeast of Valentine since the Shoemaker Collection includes a photograph of the river in that area. They made additional sightings during the return trip to the ranch in the Sand Hills.

William E. Beed, another zoologist associated with the University of Nebraska, made studies of the birdlife of the Niobrara Game Preserve near Valentine in 1934. He spent a summer there and included in his report a list of species and their associations with the biotic communities in this area which is now the Fort Niobrara National Wildlife Refuge (Beed, 1934). The most common species he noted on the uplands were the horned lark, lark sparrow, and western meadowlark. He also commented that the Preserve had a greater number of raptors than surrounding areas. His study provides valuable information for this region of the Niobrara during that time.

During the same summer, on 22 July 1934, Shoemaker rode with Harold and Margaret Cook to the Agate Springs Ranch. The weather in region had been hot and dry, but upon reaching the ranch Shoemaker wrote:

"The ranch is the coolest place I have encountered in many weeks. There are long lines, sometimes minor groves, of cottonwoods, some of them 80 feet [± 25 m] high and their girth four feet [1.2 m] from the ground exceeding ten feet [3 m]. There are lines of immense willows bordering beautifully grassed areas; there must be at least eight acres [3.24 hectares (ha)] of lawn about the ranch buildings, all watered regularly and kept in order. There is a pond of considerable extent, derived from the cold waters of the Niobrara. This pond is bordered with a multitude of cattails [Typha sp.] and other water growths. This ranch was laid out and the trees planted by Captain James H. Cook over 50 years ago."

Shoemaker hiked on the prairie and along the rocky rims, keeping notes on birds as well as looking for artifacts and enjoying a cool swim in the river. His list was 30 species, including those seen in the area of the ranch house. His conclusion for the day was: "I thoroughly enjoyed the seven hours which I spent in this wonderland which I have learned to love. [I] noticed one thing this evening on the ranch lawn which definitely interested me. It is a great place for birds; western robins, bronzed grackles, brown thrashers, yellow warblers, wrens, eastern and western kingbirds, and strangely enough, killdeer plovers, are almost always present."

Recent Observations (1955-1988)

William Youngworth spent several years studying the birdlife in the area of the Niobrara Game Preserve northeast of Valentine. His studies (Youngworth, 1955), starting in 1932, with the fourth trip in 1947, were made in response to an invitation by Frederick M. Dille, who was ranger superintendent from 1917 until 1930. The two men camped in a cabin in the woods below a small waterfall. Youngworth collected birds which Dille prepared as specimens. Most of their work was with passerine birds.

Recent attention to portions of the central Niobrara River is due to environmental studies required for the Norden Dam of the O'Neil Project. The primary facet of interest was records of birds observed along specific transects through the habitat types present on the study area (Longfellow, 1977). Longfellow also kept a list of other species observed.

The extensive studies made in the central Niobrara River Valley continued after The Nature Conservancy bought the Niobrara Valley Preserve in 1980 (Figure 3). That tract covers about 54,340 acres (22,000 ha), with its headquarters north of Johnstown in Brown County. The area was purchased because of the unique co-occurrence of ponderosa pine forest, eastern deciduous forest, northern forest, mixed grass prairie, sandhills prairie and tallgrass prairie habitats within 1-2 miles (1.6-3 km.) (Brogie and Mossman, 1983).

Once the area was purchased, the Conservancy conducted an extensive natural history survey. The birdlife was extensively surveyed daily from 4 April to 10 July 1982 and less extensively during the remainder of that summer (Mossman and Brogie, 1983). Status and breeding information was summarized for this survey period and incorporated information from local residents and other pertinent records for the following fall and winter.

Further west in the Valley, field studies have been made at Box Butte Reservoir in southern Dawes County since 1973 (Rosche, 1982). The reservoir offers high water in the spring followed by draw-downs that leave extensive exposed mud flats suitable for bird use from mid-July on. Perhaps the best stand of large cottonwood and willow habitat in the entire western half of the Valley is found at this site. Most of it is ungrazed and it provides, perhaps, the optimum riparian-type habitat available for migrant species in the entire western section of the Valley (1989: R.C. Rosche, pers. comm.). Cropland and grasslands are also found in the vicinity. These sightings add a valuable perspective on how a reservoir and its associated human-created habitats influence the occurrence of bird species. In addition to published records, more recent and current observations were provided of the diverse avifauna recorded at this site.

Many records for the town of Niobrara at its current upland site were contributed by Mark Brogie, of Creighton, NE, who also conducted bird work at the Niobrara Valley Preserve. His records, from 1986 through 1989, are primarily within a one and a half mile radius of the town of Niobrara. This includes the Valley but also the floodplain and hills where the Niobrara River empties into the Missouri River. Many dates are available through this field work but only one representative date is given in the species accounts. Status information is summarized where available.

Records for western Cherry County were provided by Lois Simmons at the Simmons Ranch south of Eli (section 6, T33N, R35W and a few miles to the west and east) and Don and Sharon Moreland at the Twisted Pine Ranch along Highway 61 south of Merriman (Sections 20 and 29, T33N, R37W). Both the Simmons and Morelands are casual observers, watching birds for personal interest.

The Simmons Ranch has a variety of typical Niobrara River habitat including river floodplain and meadow, small midriver sandbars, and coniferous and deciduous woods, and sandhills prairie on the upland. The Twisted Pine Ranch is unique in having a large open water lake with associated wetlands. There is also floodplain forest and coniferous woods on the Valley slopes. Both areas are gazed by cattle.

Ducey studies of birdlife along the Niobrara River started in 1982. Most of the sites visited were in the immediate floodplain of the river. Others are in canyons that are part of the Valley drainageway such as Bohemia Prairie or Thomas Creek Wildlife Management Area. The only upland sites included are those immediately adjacent to the river Valley.

The dates of observations were: 1982: Anderson Bridge WMA, 5-7 May, 6-7 July, 19 August and 29 September. 1984: Bohemia Prairie WMA, 16-17 June. 1985: Bohemia Prairie WMA, 8-10 June; Mariaville, 25-26 April, 11-13 June, 9-10 August and 21-22 September; Thomas Creek WMA, 25 April, 13-14 June, 9 August and 20-21 September; Schlagel Creek, 11 August and 18 September; Anderson Bridge WMA, 14-16 June and 19-20 September. 1986: Bohemia Prairie WMA, 26 May; Pishelville Island, 27 May; Elk Creek, 27 and 28 May, 4 June; Anderson Bridge WMA, 18-19 April, 28-30 May; Eagle Bluffs 30 May to 1 June; Agate Fossil Beds National Monument, 1-2 June. 1987: Agate Fossil Beds NM, 13 June 1987; Anderson Bridge WMA, 11 June, 5-6 September; Eagle Bluffs, 6-7 September; Elk Creek, 5 September. 1988: Anderson Bridge WMA, 26-27 May; McCann Canyon, 27 May.

Several different areas were visited during field trips along the entire length of the Valley: 1). Agate Fossil Bends National Monument (Sioux County). The area is about 2,000 acres (810 ha) containing five habitat types. The channel of the Niobrara is about a meter wide, with wetland meadows and marsh adjacent to the river. Also on the floodplain to a limited extent is willow in the moist lowland. Drier areas on the upland have shortgrass prairie with rocky buttes along the bluffs of the river Valley. The woodland areas are especially rich in birds since this type of habitat is limited. There are some limited groves of cottonwood trees nearby. There is a former oxbow of the river, which has been dredged and deepened in the ranch house area of Agate Springs Ranch (1989: Dorothy Meade, pers. comm.).

2). Eagle Bluffs is private land on the Niobrara south and a little east of Rushville (North ½ of section 19, T30N R43W, Sheridan County). Habitats include river channel with sandbars, wetland meadow, floodplain forest, rocky buttes with pine and upland prairie.

3). Anderson Bridge Wildlife Management Area (WMA) covers 137 acres (±55 ha) 5.5 miles (8.8 km.) south, two miles (3.2 km.) east and five miles (8 km.) south of Kilgore (Cherry County). This diverse area along one mile of the Niobrara River includes deciduous woodland on the floodplain and coniferous woods on the upland. There is a several-acre former pasture near the river that was heavily grazed in the past and a limited amount of native sandhills prairie on the upland that continues to the south into the extensive grasslands of McKelvie National Forest. Wetlands include a small pond with an excellent variety of marsh plants including water lily (Nymphaea tuberosa), cattail, common reed (Phragmites australis) and wetland grasses. There is a small stream and the channel of the river that provides additional wetland habitat. The avifauna of this area has been surveyed previously (Nebraska Bird Review (NBR) 51:62-63). Three other sites were also visited on only one occasion, including McCann Canyon on the north side of the river three miles (4.8 km.) west of Anderson Bridge WMA. The two other areas along the Niobrara River were in western Cherry County. The vicinity of Bear Creek (sections 31 and 32, T33N R36W) was visited on 20 May 1989. This area of the river in some places has only a limited amount of floodplain. Instead, the prairie typical of the uplands continues to the river bank in some places. In a few spots sandstone cliffs are immediately adjacent to the river. The Valley here changes character often with its width and amount of vegetative cover highly variable. The Twisted Pine Ranch was visited on 21 May to visit with the Moreland's about their bird sightings. A brief time was spent studying the lake and floodplain area.

4). The Schlagel Creek area is directly south of Valentine (Cherry County). The area is hayland on the floodplain and grassland and pine forest on the uplands. Deciduous trees occur along the creek and on the floodplain in groves. The land is grazed by cattle. There is also an oxbow area among the cottonwood forest. The river is fairly wide and shallow with sandbars in this area. I visited this site solely to observe the effects of wild fires which burned portion of the pine forest and prairie in 1985.

5). Thomas Creek WMA comprises 692 acres (± 280 ha) 2 miles (3.2 km.) east and 3 miles (4.8 km.) south of Springview, Keya Paha County. This rugged area is nearly 90% woodland that is predominantly ponderosa pine on the canyon slopes and bur oak in the sheltered draws. Native grasslands occur on the upland, with many small prairie tracts being invaded by sumac (Rhus glabra). Over a mile (1.6 km.) of small feeder streams with perennial water occur in the bottom of the canyon. A pond just to the south of the state property has open water and marsh habitat that attracts bird species not found elsewhere.

6). The Elk Creek vicinity is private land north of Bassett, Rock County (North 1/2 of sections 28, 29 and 30, T32N, R19W). The area I surveyed included the river channel, vegetated islands, a wetland complex of open water and emergent vegetation, deciduous woods with portions where oaks grow among conifers, and upland prairie.

7). The Mariaville site is private land along the Niobrara River 12 miles (19.2 km.) north and 2 (3.2 km.) miles east of Newport, Rock County (North 1/2 of section 35, T33N, R17W). The most interesting feature here is a natural lake of several acres. According to an analysis of aerial photos taken of the lower Niobrara Valley area, this lake is the largest open water body along the river from the eastern boundary of Cherry County east to the town of Niobrara (Ducey, unpublished maps). Wetland habitats associated with the open water include cattail marsh, shrub wetlands, hayland meadow, and small isolated potholes in floodplain forest bordering the river. The channel has extensive sandbar areas and a wooded island. Where cattle have access along the river, the area is heavily grazed preventing natural development of vegetation. The wetland meadow was cut for hay during mid-summer.

8). Pishelville Island, Knox County, has over 400 acres (± 162 ha) of floodplain forest. The island has a channel of only a few meters that separate it from the upland. Cottonwood is the predominant tree, with limited dense stands of cedar (Juniperus sp.). There are also grasslands, open water areas, wetland shrub growth, and backwater sloughs. Cattle graze the area.

9). Bohemia Prairie WMA is 680 acres (275 ha) 5 miles (8 km.) south and 4 miles (6.4 km.) west of Niobrara or 4.5 miles (7.2 km.) west and 5.5 miles (8.8 km.) north of Verdigre, Knox County. About 85% of this area is native prairie, including a very limited area of a sandhills blowout which is uncommon this far east. Deciduous woodland habitat occurs along creeks in the northwest and northeast corners. These woodland habitats are a part of the Niobrara Valley with the river about one-half mile (0.8 km.) to the north. There are also two small ponds. Nebraska Game and Parks Commission personnel have planted conifers and other woody plant species in the prairie, supposedly to increase habitat diversity for game birds. This will affect grassland species occurrence as the woody vegetation becomes a predominant feature of the landscape.

Niobrara River Habitat

River Characteristics

The Niobrara River Valley has an obvious physiographic change from west to east. At Anderson Bridge WMA the Valley is narrow with rugged buttes and steep canyon walls. The deciduous vegetation is limited to a narrow band along the river. Farther east, the Valley is enclosed by rolling hills with a gentle grade to the floodplain. Deciduous plants grow up the ravines and are more common on tributaries on the upland. The river in the east is wider and has numerous open sandbars in the channel. In central Cherry County, midchannel habitat is limited to very small, vegetated islands in a narrow channel. In Sheridan County the river is more open, flowing through a Valley predominantly of grassland with limited growth of deciduous trees on the floodplain and pines on the Valley slopes. The river is in a narrow channel with sandbars regularly. In Sioux County the Niobrara is narrow, with grassland predominant in the Valley.

Habitat Types

Several floristic studies have defined the separate biotic communities of the Niobrara Valley (Beed, 1934; Tolstead, 1942; Harrison, 1980). Information from each report, plus additional observations made by the author is summarized to characterize the diverse habitat available for birds along the river. There are many species of grasses, trees, shrubs and forbs in the habitat types given; only a few are given to indicate the more notable or predominant plant species. Plant nomenclature is based on the Flora of the Great Plains (Great Plains Flora Association, 1986).

Floodplain forest: the predominant species on the lower river is the cottonwood (Populus deltoides) and also American elm (Ulmus americana) and common hackberry (Celtis occidentalis). At Pishelville Island and elsewhere, the cottonwoods grow to a huge size. The forest area can be a mix of small open areas with grasslands, some wetland area, shrubs and other woody vegetation similar to the deciduous forest. Typical birds include songbirds such as vireos, warblers, the black-capped chickadee and white-breasted nuthatch. This forest is often used by great blue herons for nesting colonies.

Deciduous upland and stream side forest: the most obvious species is the bur oak (Quercus macrocarpa), with American elm (Ulmus americana), green ash (Fraxinus pennsylvanica) and box elder (Acer negundo) also representative. Birds include the Cooper's hawk, turkey, house wren, great blue heron, robin, orioles and the northern cardinal.

Coniferous forest: ponderosa pine (Pinus ponderosa) is the predominant tree. This community is also known for the cedar. Representative birds include the common poor-will, red-breasted nuthatch and chipping sparrow.

Spring-branch community: occurs to a limited extent in the central Valley area on the southern slope. Two distinct forest types have been recognized: the linden (Tilia americana)-cedar-ironwood (Ostrya virginiana)-ash forest in which white birch (Betula papyrifera) also occurs. The white paper birch forest is the secondary forest type in this community. Bird species that use other deciduous woodlands also occur in this habitat. An open-springs vegetation type, with sedges and rushes (Juncus), also has been characterized. Many rare and unusual plant species have been identified as components of this floral community (Harrison, 1980).

Shrub communities: represented by wild plum (Prunus americana), chokecherry (Prunus virginiana), buck brush (Symphoricarpos occidentalis) and buffalo-berry (Shepherdia argentia). Sumac (Rhus sp.) is a shrub which invades prairie areas. Representative birds are the gray catbird, rufous-sided towhee, loggerhead shrike and yellow-breasted chat.

Emergent wetlands, lakes, and shrub wetlands: wetlands occur in many places along the entire river. There are but a few natural lakes and two man-made reservoirs. Marsh vegetation includes cattails, sedges (Carex sp.), bulrush (Scirpus sp.), common reed (Phragmites australis) and arrowhead (Sagittaria latifolia). Marsh birds are best represented by the red-winged blackbird. Shrub wetlands have a predominant growth of willows and are used most notably by swamp sparrows which have a very localized occurrence. The lakes are a mix of open water, floating vegetation and emergent wetlands near the lake edge. Notable plants include white water lily plus the same plants typical of emergent wetlands. Lakes are used by a large number of migrant birds including waterfowl, pelicans, black terns and others. The Mariaville area has many of these habitat types within a relatively small area, with the shrub wetland the most unique. At the Elk Creek site, there is a lake area with several wetland communities.

Wetland meadow: typical plants are bluestem (Andropogon gerardii), Indian-grass (Sorghastrum nutans), bluejoint reedgrass (Calamagrostis canadensis) and tall dropseed (Sporobolus asper). The eastern meadowlark and bobolink are the most characteristic species. The largest wetland meadow I visited during my field studies was annually cut for hay as are the majority of the meadows in the Valley.

Sandhills prairie: representative flora are the bluestem grasses (Andropogon sp.), switchgrass (Panicum virgatum), indian-grass, needle and thread (Stipa comata), Canada wild rye (Elymus canadensis), blowout grass (Redfieldia flexuosa), hairy grama (Bouteloua hirsuta) and other types of grasses. Species occurrence varies with available moisture. Yucca (Yucca glauca) occurs in places where the grassland has been overgrazed. Typical bird species include the grasshopper sparrow, horned lark and vesper sparrow.

Tallgrass prairie: typical plants include big bluestem (Andropogon gerardi), indian grass, and switchgrass. A transition from wet meadow, to tallgrass prairie and then to upland prairie occurs with changes in available moisture and ground elevation. This habitat is limited since most of it has been tilled for the planting of agricultural crops. Typical birds species include the meadowlark and grasshopper sparrow.

Mixed prairie: grasses such as needle-and-thread and blue grama (Bouteloua gracilis) with a sedge (Carex filifolia) are typical. Bird species include the grasshopper sparrow, horned lark, western meadowlark, and vesper sparrow which are typical in almost all grassland habitats mentioned.

Shortgrass prairie: occurs on the upland and is comprised mostly of buffalo grass (Bulbilis dactyloides) and blue grama grass. A representative area is Agate Fossil Bed NM. Typical birds include the long-billed curlew, McCown's longspur, western meadowlark and horned lark, to name a few. The mixed grass and short grass prairie areas have similar species of birds which occur.

Riverine sandbars: mid-channel sandbars with a varying amount of vegetation. Plants on an open sandbar include cottonwood saplings, short growths of cattails, sedges, willows (Salix sp.) and annual weeds. The most extensive growth of vegetation is represented by cottonwoods and willows. Characteristic species when vegetative cover is limited (typically less than five to 10 percent) are cranes, the piping plover, and least tern, and many other shore and water birds when vegetative growth is still sparse. An increasing growth of plants means a transition in bird species to such species as the Bell's vireo and yellow warbler.

Rocky buttes and cliff faces: bare rock cliffs near the mouth of the river which have no vegetation. The characteristic species is the cliff swallow. In the western Valley the rocky buttes have a mixture of grassland, woods and scattered bare rock. Characteristic species are the rock wren and common nighthawk. In this area, sheer rock faces with a ledge suitable for nest building may be used by golden eagles, prairie falcons, ferruginous hawk and red-tailed hawk. The Say's phoebe occurs in the grassland areas of this habitat and nest in crevices and holes in the rocky buttes and cliff faces.

Most of the bird studies that noted floristic conditions along the Niobrara River noted the obvious differences in habitat characteristics of the Valley from east to west. These changes can be shown with photographs of the areas I visited during my recent studies (Figures 3-8). The habitat differences are due to different physiographic features of the river Valley (Figure 9). The Valley in the east has a more expansive river bed and floodplain. The central Valley has deeper canyons that offer more shelter from harsh growing conditions which allows a greater diversity of flora to thrive. The western Valley, near Agate, is open country of mostly grassland with some woody vegetation right along the river.

A comparison of the same area where Frank Shoemaker took his photo in 1903 shows an increase in woody vegetation. In some localities, cattle grazing in recent years is causing a decrease in woody vegetation.

Quantitative studies have been done on the habitats of the river channel. An extensive survey of riverine habitat features along the eastern Niobrara River was conducted as part of environmental studies associated with the Norden Dam project (Environmental Research and Technology, 1981). Identified habitat types and typical plant species, characteristics of habitat types and prepared maps showing the land cover types of the river channel from the Norden Bridge east to the Highway 137 bridge in Rock County are the basis for the report. It shows that the prevalent land cover types along the river are the channel area itself, riparian woodland, hay meadows and pastureland.

As outlined in this report, the successional sequence along the lower Niobrara River shoreline is:

1). mixture of herbaceous species and shrub and tree seedlings established on barren sand

2). seedlings of shrubs - willows, indigo bush (Amorpha fruticosa) - increase in height, and develop large intermeshed root systems

3). tree saplings (green ash (Fraxinus pennsylvanica), cottonwood) begin to overtop surrounding shrubs

4). shade-intolerant shrubs (willows) begin to die out as canopy cover of the taller trees increase (Environmental Research and Technology, 1981, p. 3-40 to 3-58)

Bird Species

Whooping Cranes

There have been eight confirmed sightings of whooping cranes on the Niobrara River since 1957. All have been between Carns and Fort Niobrara NWR (Nebraska Game and Parks Commission 1988). The numbers varied from one to five, with an average of three. Site features, when given, were characterized by sandbars with no emergent vegetation in an area where the river was wide, braided, and shallow.

Piping Plover And Least Terns

The first reference that the Niobrara River was important breeding habitat for these birds was made by Wolcott (Ducey, 1983). During his float trip down the river, he first noted four plovers near the Springview Bridge. He later found the nest. During the remainder of the trip, he located no nests but noted plovers commonly. He did not see terns until further downriver near Badger, Holt County, when a flock of eight or nine birds was seen. From there downriver terns were very common and he noted them daily. Wolcott's notes also said that "every large bar was certain to have several of the little fellows hovering about, uttering their harsh, squeaky notes as they plunged into the shallows or chased each other about in the air."

Historic studies give some insight into the occurrence of the piping plover and least tern. They do not however provide an overall perspective. Once the plight of these two species became apparent to biologists in the modern era, more extensive work was initiated to provide accurate and current information needed to assist in developing management plans to ensure the continued survival of the species.

The Nebraska Game and Parks Commission has been conducting annual surveys of piping plover and least tern population since 1980 with the exception of 1986. The first efforts were aerial surveys with a follow-up check of areas where birds had been seen. In 1985 and 1987, more thorough surveys were done by a thorough search of the sandbars after birds were observed from the adjacent water channel while passing by on an airboat. The number of birds noted at colonies varies from one to more than 26. Most of the colonies have from six to 20 terns, with more than 25 sites having 6-10 terns.

Populations and number of sites where recorded for Piping Plovers and Least Terns on the eastern Niobrara River (Information courtesy of Nebraska Game and Parks Commission).
	Norden to Highway 137				Highway 137 to Niobrara				Total
	PIPL(1)	# (2)	LETE (3)	#	PIPL	#	LETE	#	PIPL	LETE
1980	-- (4)	-	20	1	--	--	96	9	--	116
1981	10	1	7	1	82	5	90	8	92	97
1982	8	1	25	1	4	1	62	7	12	87
1983	6	1	9	2	83	7	126	7	89	135
1984	6	1	16	2	32	5	79	6	38	95
1985	16	2	24	2	84	12	150	12	100	174
1987	8	1	10	1	101	11	133	11	109	143
(1) Piping Plover. (2) Number of sites where recorded. (3) Least Tern. (4) Populations were not surveyed.

In some years, floods may decimate nesting populations by washing away nests. This was recorded most recently in 1987, when all known nesting attempts were destroyed. Nests are easily flooded because their height above water averages only .43 feet (±102 mm) for the piping plover and .56 feet (± 128 mm) for the least tern (Nebraska Game and Parks Commission, unpubl.).

These studies indicate the Niobrara River, with its extensive amount of water and sandbar channel area provides important nesting habitat for these threatened or endangered birds.

Other shorebirds also occur along the river channel. To assess use of the river by all shorebirds in the summer, two approximately five mile (8 km.) stretches were surveyed in June, 1985. The areas are near Pishelville, Knox County (southwest 1/4 sec. 24, T32N, R8W to northeast 1/4 sec. 3, T31N, R7W) and near Redbird, Holt County (northwest 1/4 sec. ;6, T32N, R10W to north 1/2 sec. 11, T32N, R10W). I did the census by walking in the river channel and counting the birds seen or heard.

The estimated shorebird and waterbird numbers recorded are given here to indicate relative abundance along these portions of the Niobrara River. Since no specific nesting areas for plovers or colonies of terns were noted, this does not indicate populations but shows the differences in the number of these birds that occur.

Number of breeding season waterbirds noted in two locales on the lower Niobrara River.
Census Area	Piping Plover	Killdeer	Spotted Sandpiper	Least Tern
Pishelville	4*	22+	16+	6+
Redbird	0	4+	10+	3+
*Based on a pair per site of observation.

Piping plovers were the least obvious. Killdeer were very obvious and easy to count. Spotted sandpipers were as common or numerous as Killdeer but may have been present in greater numbers. They were not as vocal and occurred in vegetation on the sandbars, islands and shore which made them sometimes less obvious.

During this census, I noted that over 75% of the sandbars in the eastern portion of the Pishelville census area were overgrown with willows. The growth of vegetation reduced the habitat available to these species. At one open sandbar area less than 25 yard (± 23 m) in diameter, terns showed defensive behavior, but no breeding activity was located and the birds left the vicinity. This was the only suitable nesting substrate in the immediate area. Riverine sandbars upstream were of better quality being more extensive and open and occurred to a greater extent.

Changes may have occurred over time as the river's flow has varied during the past decades. The pool of Lewis and Clark Lake has reduced the scouring effect of riverine sediment. As the river nears the water level of the reservoir, the sediment is deposited in the riverbed. This deposition has resulted in an increase in sandbars. As a result, vegetative encroachment has occurred. Higher than average flows would deposit more sediment among the vegetation on the sandbars and further increase the height of these areas above the river water level. This would decrease the ability of water flows to scour the sandbars clean of any plant growth. The Corps of Engineers has studied this portion of the river to determine the effects that would occur if the pool level of Lewis and Clark Lake were increased. No actual measurements have been made of the influence of this water structure on the riverine habitat of the Niobrara near the Missouri River.

Wintering Bald Eagles

Habitat along the Niobrara River is suitable for bald eagles in the winter and during spring and fall migration. In addition to regular sightings at a specific area, there have been annual surveys since the 1950's of eagles. Only information since 1980 is given here because the counts were made using the same, standard survey method.

Number of Bald Eagles counted in National Wildlife Federation midwinter surveys along the Niobrara River (Information courtesy of Nebraska Game and Parks Commission).
	1980	1981	1982	1983	1984	1985	1986	1987	1988
Region 1	15	19	6	21	3	11	10	33	13
Region 2	27	22	24	29	11	25	22	54	25
Region 3	--*	--	2	2	2	--	3	--	3
Region 4	1	--	--	--	--	--	2	--	--
Totals	43	41	30	52	16	36	37	87	41
* indicates no birds were sighted during the survey

During these surveys the number of eagles present were counted for certain stretches of the river. To allow a geographic comparison, these stretches were placed within the five river sections designated for this paper. The five sections are further described in the species accounts portion of this paper.

The census information shows a greater use by eagles of the river east of the Valentine area. Although no bald eagles were seen west of Dawes County during the midwinter census, the species does occur in that area based on sightings in the Agate Fossil Beds NM area and elsewhere in Sioux County.

Based on the rare occurrence in summer, and the breeding activity of these eagles elsewhere in Nebraska (Ducey, 1988), it could be expected that the bald eagle may eventually nest in suitable areas along the Niobrara River.

Avian Population Studies

Only two surveys have been made to quantitatively assess bird use of the Niobrara River Valley, both for the environmental studies for the O'Neill Project. The first survey of bird use of the river channel was done by the Fish and Wildlife Service (FWS). The FWS conducted two surveys and separated their numbers into four river segments between Highway 137 and Smith Falls (Longfellow, 1977). The counts were done in October and November of 1976 and April of 1977. The information for each segment has been combined and summarized. Average values have been rounded to the nearest full integer.

The fall survey counted unidentified ducks on 13 of 14 surveys, with a range in numbers of 20 to 228, averaging 74. Eleven of the 13 counts were between 20 and 95, averaging 42.

Spring counts by the FWS were more inclusive and noted a larger variety of species. American white pelicans were counted four times with numbers of one, seven and 15 seen twice. Double-crested cormorants were noted on nine of 15 counts with a range of one to 25, average 7. The high values were 11, 13 and 25 with the remainder between one and five. Great blue herons were seen on seven of the 15 surveys. Usually only one bird was seen in a river segment but on one occasion seven were seen. The spring count included mallards, pintails, blue-winged teal, wood duck and northern shovelers and recorded these ducks on 14 of 15 surveys. The range was 20 to 228, average 75, with 11 of 13 counts between 20 and 95, average 42. Common mergansers were seen on 12 of 15 surveys. Numbers ranged from two to 23 and averaged 14. Four counts were less than five, five were between 10 and 20 and there were three counts of more than 20 common mergansers.

Sandhill crane numbers are available for the fall period only. Survey counts between four and 2,850 were made on nine of 14 surveys. The average was 568 with an average of 251 for the seven counts between 120 and 1,030 birds.

Numbers of sandhill cranes counted during a fall aerial survey of the Niobrara River (Longfellow 1977).
Date *	Highway 137 to Highway 7	Highway 7 to Meadville	Meadville to Norden Bridge	Norden Bridge to Smith Falls	Total
22 Oct	76	150	660	220	1,030
23 Oct	--	350	--	100	450
26 Oct	--	150	--	--	150
27 Oct	--	--	4	--	4
28 Oct	--	100	100	--	200
29 Oct	--	150	--	--	150
31 Oct	--	120	--	--	120
3 Nov	1,600	1250	--	--	2,850
4 Nov	160	--	--	--	160
* No sandhill cranes were seen on 24, 25, 30 Oct. and 1, 5 Nov.

The second study was done of five transects through representative habitat in the Niobrara Valley. Studies were carried out in the spring and fall (Longfellow, 1977). In addition to those birds listed, additional species were seen but no density value was designated. The most abundant species were the western meadowlark, horned lark, mourning dove, house wren, black-capped chickadee, northern oriole, red-winged blackbird, and lark sparrow. "Populations of each species noted during this study are lower, on the average, than those in areas where larger stands of comparable habitat occur" (Longfellow, 1977; attachment 5, p. 20). That study noted how the many ecotones contributed to the number of species recorded.

Avian Hybridization

The mix of habitats that occur in the Niobrara River Valley provides ideal conditions for the co-occurrence of several bird species that may hybridize. Specific studies have shown that hybridization has occurred between what were once called red-shafted and yellow-shafted flickers; lazuli and indigo buntings; and what were once called Bullock's oriole and Baltimore oriole (Sibley and Short, 1959; 1964; Short, 1961; 1965). The Niobrara Valley area in the vicinity of Valentine was noted to be the center of the zone of hybridization for the orioles and buntings.

These same studies have mentioned the possibility of hybridization occurring between the western and scarlet tanagers, rose-breasted and black-headed grosbeaks, and western and eastern wood-pewees. Distribution records indicate that during the period of record the tanagers have had overlapping ranges. However, the western tanager is apparently erratic in the vicinity of Valentine whereas the scarlet tanager is common eastward from Valentine. Sites where the wood-pewees were noted indicate an overlap in their range. This has been recorded at Box Butte Reservoir on the western Niobrara River in Dawes County. The western wood-pewee is common while the eastern wood-pewee is rare in the same area during the breeding season. A hybrid eastern and western wood-pewee was noted in Valentine in May 1989 (1989: R.C. Rosche, pers. comm.). Additional field work could better define the portion of the Valley where these species overlap and occur with some regularity during the breeding season.

Species Summary

In order to better assess any changes bird species occurrence through time, two conventions are followed in the summary of species. First, the river is divided into five stretches selected to represent the different character of the river and where observations seemed to be grouped. Time periods selected are similar to previous work done with Nebraska birds (Ducey, 1988).

The regions for the species listing table were:

Region 1: The easternmost stretch of the Niobrara River, including the area around Niobrara, Bohemia Prairie WMA, Pishelville Island, and the mouth of the River.

Region 2: Includes areas of Mariaville, Elk Creek, Thomas Creek WMA, the Niobrara Valley Preserve and historic Fort Niobrara Game Reserve (now the Fort Niobrara NWR).

Region 3: Central and western Cherry County in the vicinity of Anderson Bridge WMA, south of Eli and south of Merriman at Highway 61.

Region 4: The river Valley in Sheridan County south of Rushville on private property designated the Eagle Bluffs area.

Region 5: Box Butte Reservoir and westward to the vicinity of Agate Fossil Beds NM.

Time Periods of A = Pre-1920; B = 1921-1960; and, C = Post-1960, were used to evaluate any changes through time in the distribution of birds along the Niobrara River. Habitat changes have occurred due to increased woody vegetation growth following the suppression of prairie fires. Construction of two reservoirs has provided open water habitat that was historically not present.

Discussion

Extensive habitat diversity supports a large number of different species in a small area. The number of bird species currently recorded along the Niobrara River is 268. The review of species in this paper also illustrates unknown occurrence areas in a species range. Additional field work could help fill in the range of some species and lead to a better understanding of the avifauna of the Valley.

The valley is a transition area for eastern and western avifauna. From west to east the habitat and bird composition change. The dominance of prairie gradually changes to a predominance of woodland in the east.

This lower portion of the Niobrara is noted for its wide and shallow river with many bare sandbars. Here lakes on the river floodplain are larger and deeper, whereas at Anderson Bridge the lake size is a result of dam-building efforts by beaver. These water areas attract a large variety of shore and water birds. In the western portion of the Valley, Box Butte Reservoir attracts many species that add to the diversity of the Valley bird list. Especially notable are the shore and waterbirds. Loons, grebes, waterfowl and gulls are examples. Many of these species would probably not occur in the Valley if it were not for the habitat created by the reservoir. The most obvious reason for this difference, I suggest, is the natural riverine and wetland habitat in this region of the river, which is not as extensive elsewhere in the Valley. If these species were to occur elsewhere in the undeveloped portion of the Valley, it would probably be in the lower reaches of the river. At Spencer Dam on the eastern river, the same type of extensive use by a variety of waterbirds would not be expected since there is no large body of deeper, open water.

Of the total number of species included in this paper, over 75 are associated with wetland or riverine habitats. This does not include the red-winged blackbird or killdeer and others which occur in diverse habitats. This is about one-fifth of the total and illustrates the importance of riverine habitat. Included in this category are several threatened or endangered species - the whooping crane, bald eagle, piping plover, and least tern - which points out the importance of conserving mid-river sandbars to be used by a number of shore and water birds. Habitat is available now but there are some changes that could alter this. Near the mouth of the Niobrara, the scouring effect of river flows has declined as the pool level of Lewis and Clark lake became established. This has led to an increase in the growth of vegetation on sandbars. The Corps of Engineers once proposed raising the pool level behind Gavins Point Dam which would further influence channel habitat in the easternmost area of the Niobrara. Extensive changes in flow regimes could also affect the sediment and scouring features of the river water. Limited habitats such as wetland lakes and wet meadows also need protection from destruction and degradation. Retaining floodplain forest is essential for species to mix and provide the habitat overlap needed for hybridization. Reservoirs in South Dakota have flooded and subsequently destroyed woodland habitat where flickers and orioles occur and hybridize (Anderson, 1971) and this could also happen in Nebraska.

The analysis of records shows some notable apparent changes in the distribution of three species in particular. The Swainson's hawk once nested and was a regular summer resident at the Niobrara Game Preserve area but current records list it only as occasional. The rock wren once was said to also nest in the central Valley area but now is listed as rare there. Nesting habitat is present but actual nesting has not been confirmed for the current period in the central Valley which is the fringe of the normal range for this wren. The barred owl was listed as an uncommon resident at Fort Niobrara by Youngworth (1955) but has only recently been recorded in the easternmost portion of the Niobrara Valley. The raven and tufted titmouse were recorded in the recent time period but there are no records for the current period.

There are some other notable items on species range based on the information. Two species, the merlin and red crossbill, have been noted for the area of the Valley which have an extensive growth of pines - the preferred habitat of the crossbill during the breeding season.

The benefits of further field work can be indicated by more sightings of migratory songbirds. Regions 1 and 2 have a larger number of warblers seen than any other region, resulting from field work done at the Niobrara Valley Preserve and near the junction with the Missouri River.

The western Valley has species limited to the region, including: Cassin's kingbird, western wood-pewee, green-tailed towhee, McCown's longspur. Many migratory species associated with Box Butte Reservoir have been recorded only at this site.

There are some records from this area also which are unverified and unaccepted sightings. At Agate the range of the ruby-throated hummingbird would have a lengthy extension from the central Valley from its previously reported range. The rufous hummingbird, Selasphorus rufus (Gmelin), is the species expected in this area and the broad-tailed hummingbird, Selasphorus platycercus (Swainson) also occurs occasionally as migrants. The red-shouldered hawk, chukar, green jay, ruby-throated hummingbird, and groove-billed ani are unexpected and unverified state records.

Based on personal field work, it was noticed that changes in vegetative character may promote changes in bird species distribution. No quantitative data was collected but the extent of shrub growth has increased here. Several species were observed at Anderson Bridge in 1985 that had not been noted in 1983. Recorded in 1985 but not noted in 1983 at Anderson Bridge WMA were the: black-and-white warbler, red-bellied woodpecker, hairy woodpecker, yellow-breasted chat, great-crested flycatcher and indigo bunting.

The chat in particular would be expected to find more suitable habitat on the area as vegetative growth increased once cattle grazing was stopped. At Anderson Bridge WMA, livestock removal has led to a continual increase in the growth of shrubs and other plants. Ovenbirds, which also occur in the woodland understory, would also benefit from greater vegetative cover.

Cattle have a drastic effect on the character of the vegetation throughout the Valley. This impact is most obvious in the floodplain forest. At Mariaville the floodplain forest was void of any understory vegetation due to the grazing and trampling by cattle. In the western Valley, only the sides of steep north-facing slopes have any significant riparian vegetative growth. Cattle not only prevent seasonal plant growth but also prevent any new growth of trees and shrubs. At Anderson Bridge WMA, the growth of vegetation in the woodland understory is remarkably different from adjacent areas used as pasture for cattle. Shrub, grasses and other plants grow undisturbed and provide significant wildlife cover.

Along the entire Valley, the only decent riparian growth is limited to wildlife refuges, wildlife areas and other public lands. Marshes, especially along the edge, are disturbed by cattle, although these animals may not walk into the deeper water areas so plant growth here may occur undisturbed. In some canyons on private land, the steep and rugged terrain may limit cattle access and allow growth of deciduous and coniferous vegetation. Grassland areas can also have little or no plant growth where cattle grazing occurs. Cattle also graze on sandbars. In the long term, overgrazing has lead to a decrease in floodplain forest since no regeneration of trees and shrubs can occur.

Another additional impact on the river occurs below the dam at Box Butte Reservoir. Here the river is little more than an irrigation canal used to transport water to the Mirage Flats area south of Hay Springs where agricultural crops are grown. One other agricultural practice has an influence on the occurrence of some birds. Alfalfa is always irrigated in the west part of the Valley, hence it provides and artificial man-made habitat for eastern meadowlarks, bobolinks, dickcissel ad perhaps ring-necked pheasants (1989: R.C. Rosche, pers. comm.).

An increase in vegetative growth in the Valley would promote the occurrence of birds and increase their range since habitat conditions would be improved. For eastern species, suitable habitat would especially occur to a greater extent further west along the Niobrara River.

Some changes in occurrence may be due to shifts in range on a short term basis. The indigo bunting was very obvious in 1985. The red-bellied and hairy woodpecker have also been observed only during one season at Anderson Bridge.

It has been noted that bird populations are smaller because the extent of available habitat is less (Longfellow, 1977). Changes in bird populations are most evident on the edge of their range. This may be the reason for changes in species occurrence in this region of the Valley.

In one case, a gradual but continual increase in range has also been noted in the Valley. The northern cardinal was very uncommon at Anderson Bridge in 1985; only one singing male was present in a small tract of deciduous woods. By 1988 there were at least two pairs of territorial birds. In the early 1950's, Youngworth noted the species was moving west along the river from the area of the Fort Niobrara Game Preserve. There were no historic sightings previous to the mid 1900's despite field work in the area. Apparently the cardinal has become established in the Niobrara Valley only during this century.

The wood duck has also extended its range. It was not recorded during any field studies prior to 1960 but is now known to occur along most of the river. This duck has extended its range westward with an increase of woody vegetation. Within just the past few years, wood ducks have been added to the bird list at Agate NM and Box Butte Reservoir.

In addition to the well-documented co-occurrence of several species, the Valley also has other bird species of similar taxonomic classification which occur in the same areas. Three species of nightjars have been noted in the area of Bohemia Prairie (Ducey 1985), at the Niobrara Valley Preserve (Brogie and Mossman, 1983) and at Thomas Creek WMA (1989: R.C. Rosche, pers. comm.). At Anderson Bridge WMA, four species of woodpeckers were seen in a single day of birding. Among these was the red-bellied woodpecker which now occurs as far west as central Cherry County whereas it was previously noted only in the Valentine area. This woodpecker is fairly common from the vicinity of Bohemia Prairie to the junction of the Missouri River (1989: M.A. Brogie, pers. comm.)

The Niobrara Valley is recognized for having disjunct or range extension in the Nebraska region. This paper indicates there are 15 species which have range extensions in the Valley. Many of these species are associated with woodland habitats or wetland habitats. These species have a range extension in their know range in Nebraska. A range extension does not necessarily mean the Niobrara River provides a corridor to a birds' range elsewhere in other regions or states.

Species noted to have range extension or limits in the variety of Niobrara River valley habitats, include.

• Prairie falcon: eastern limit, sandstone cliffs

• American woodcock: western limit, riparian woodland

• Whip-poor-will: western limit, woodland edges

• Red-bellied woodpecker: western limit, open woodland

• Western wood-pewee: eastern limit, pine woodland

• Eastern wood-pewee: western extension, riparian woodland

• Blue-gray gnatcatcher: western limit, riparian woodland

• Wood thrush: western limit, deciduous woodland

• Yellow-throated vireo: western limit, riparian woodland

• Black-and-white warbler: western extension, deciduous woods

• American redstart: western extension, riparian woodland

• Ovenbird: western extension, deciduous woodland

• Scarlet tanager: western extension, oak woodland

• Western tanager: eastern limit, pine woodland

• Black-headed grosbeak: eastern limit, open deciduous woodland

The American woodcock is an eastern and northern species whose range has reached the lower Niobrara River as it has been recorded near the confluence with the Missouri River (1989: M.A. Brogie, pers. comm.) and along the rivers edge at Spencer Dam (1989: R.C. Rosche, pers. comm.). The blue-gray gnatcatcher is a second species which is apparently extending is eastern range into the lower Valley. Both are expected to probably breed in this area. If woodland and wetland habitat along the river was in better condition - floodplain forest and prairie not over grazed and meadows not hayed - species would find suitable conditions to extend their range further. This is especially the case with the birds which occur in the deciduous forest, floodplain forest and shrub habitats along the river.

The prairie falcon nests in western Cherry County in the sandstone bluffs adjacent to the river channel. This is the easternmost site record for the prairie falcon in Nebraska. The northern cardinal has reached Anderson Bridge WMA and been seen once in spring along the river at the Simmon's Ranch about 40 km (25 miles west). If suitable habitat is present, this species would be expected to eventually occur further west.

Two probable breeding species have indications of a possible increase in range. The northern mockingbird was noted along the river at Elk Creek. The Niobrara provides suitable habitat to connect the usual eastern habitats with suitable sites in the west. The scissor-tailed flycatcher has been noted as a vagrant in the spring and into the summer in the central and western Valley, respectively. Breeding season occurrence would extend this bird's range farther north. A semi-open mix of woods and grasslands habitat is present in the many ecotones in the Valley area.

It has been pointed out that reservoirs along the Missouri River have destroyed habitat where species would overlap and hybridization could have occurred (Anderson, 1971). Along the Niobrara, a reservoir would have the same impact by destroying habitat in a zone of hybridization for several species.

The loss of woody habitat would also destroy a corridor that connects a species range with outlier areas such as the Pine Ridge and Black Hills where species are known to nest. Examples of species where this would occur include the eastern bluebird, tree swallow, white-breasted nuthatch, red-eyed vireo, American redstart and ovenbird.

Those species with an extension in their range in the Valley clearly indicate the Niobrara provides suitable habitat to create a connection between eastern populations along rivers such as the Missouri and western breeding populations in the Pine Ridge and Black Hills. Some species also have habitat suitable to extend their range either further to the west or eastward.

The Niobrara River Valley habitats are a diverse and important biological setting for a large variety of avifauna. Maintaining this biological setting is important not only for the avifauna but for the relict plants as well. The Niobrara Valley is a modern faunal refugium from the arid and treeless surrounding grasslands (Kaul et al., 1988). The Valley provides important habitat for species hybridization and serves as a corridor to connect different populations of breeding birds. The key is retaining the habitat conditions necessary for the flora and animal life to thrive and maintain the ecological setting. Conserving the habitat will also allow the changes in bird range to continue without any interference from human development.

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