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Platte River Ecology Study

Whooping Cranes

Historical Perspective

Past history

Whooping cranes presumably were common in Nebraska early in the l9th century. In 1820, Thomas Say observed that "great flights of geese, swans, ducks, brant and cranes have been passing up the (Missouri) river" arriving 19 March opposite Engineer Cantonment (Fort Calhoun, Washington County, Nebraska) (Allen 1952). Swenk (1933) suggested that "the cranes" noted by Say must have been whoopers although the date listed is almost 2 weeks before the normal start of the whooping crane migration. Allen (1952), however, thought that the "great flights ... of cranes" were chiefly sandhill cranes, with perhaps an occasional whooper present. The first reports of whooping cranes in the Platte River Valley came following the establishment of the Oregon Trail in 1841, the Mormon Trail in 1847, and the arrival of significant numbers of settlers.

The first detailed list of whooping crane sightings in Nebraska was published in the early 1930's (Swenk 1933). A total of 93 sightings from Nebraska, involving 998 migrant cranes (1912-33), was documented in this publication. Only 45 sightings involving 147 whooping cranes were made outside of Nebraska during this period. Most of the Nebraska sightings were in the Big Bend region of the Platte River Valley.

Swenk (1933) was the first to indicate the importance of the Platte River to migratory whooping cranes and based his conclusions on four factors: (1) the large number of sightings from the Big Bend, (2) the scarcity of sightings from other areas, (3) discussions with old-time hunters who spoke of large flocks of whooping cranes visiting the Platte in spring, and (4) Swenk's belief that the cranes made a mid-migration stop to feed and rest in the Platte region. His findings, however, were based solely on the fragmentary data obtained from the literature.

Sightings during 1934-44 were compiled by Brooking (1934, 1943a, 1943b, 1944) and were published as lists of observations and a report on the status of the species.

Knowledge of whooping crane habits expanded markedly in the early 1950's with publication of a monograph by Allen (1952). He re-assessed the sightings reported by Swenk and Brooking and developed a list which he felt represented valid sightings in Nebraska for the period 1820-1948. In the monograph, many of the sightings reported by Swenk and Brooking were eliminated. The final list totaled 123 sightings of which 87 occurred in counties bordering the Platte River. Allen also believed the Platte was a major stopping area for whooping cranes on the basis of the same criteria described earlier but there still remained a rather fragmentary picture of the crane's overall distribution during migration.

Recent history

Whooping crane use of the Platte River apparently has declined markedly in recent decades. Confirmed sightings of these birds on or near the Platte River during 1912-49 are provided in Appendix C. During the past 30 years (1950 - spring 1980) there have been only five confirmed sightings of whooping cranes on or near the Platte River. The sightings have been made from Overton eastward to Chapman, and four have been within the areas designated as critical habitat for the species (Federal Register 15 May 1978) (Fig. 13). Three of the sightings have been in spring (17-18 April 1980; 19 April 1980; 4 May 1950) and two in the fall (21-22 October 1966; 31 October - 1 November 1974).

Information regarding the habitat use and behavior of the cranes exists for four of the sightings. The five birds observed northeast of Phillips on 21-22 October 1966 were first seen loafing on sandbars in the middle of the Platte just upstream from the Chapman Bridge on 21 October. These birds roosted overnight in the same area. At 0730 on 22 October the cranes were seen on a wheat field about 5 miles southwest of their river roost site. The birds flew back to the river for a brief time and then departed at about 1100 to continue their migration. They were tracked by automobile to the vicinity of Red Cloud, Nebraska approximately 100 km to the south of the Platte River.

The two adults observed 3.2 km (2 miles) east of the Minden Interstate Highway 80 interchange on 31 October - 1 November 1974 used the Platte for loafing, feeding, and roosting. These birds loafed on the sandbars in the middle of the river and probed in adjacent shallow waters. Movements of approximately 0.8 km (0.5 mile) upstream and downstream from the roost site were observed and on at least one occasion the cranes were observed feeding in a cornfield on the south side of the river.

The pair seen on 17-18 April 1980 were also located just east of the Minden I-80 interchange. They were first observed at 0645 feeding in a recently disced cornfield 3.2-4.8 km (2-3 miles) from the river. Feeding continued until 0815, when the cranes flew to the Platte River and loafed there for about 25 minutes. The birds left the river at 0845 and were seen at 0930 in a plowed cornfield 1 mile south of the river. Observations ended after a few minutes because the birds left the area. When relocated at 1030, the cranes were foraging in a recently burned pasture on the Lillian Annette Rowe Sanctuary of the National Audubon Society. Although foods taken by the whooping cranes were not identified, sandhill cranes collected while foraging in similar habitat in the same general area were feeding on earthworms. The whooping cranes left at 1100 and were not observed until 0820 the following morning, at another location on the Platte River. Observers suspected that the birds had roosted in that spot overnight. These cranes were observed loafing, preening, dancing, and probing in the shallow water. The cranes left the river at 0845 and were not seen again.

Seven whooping cranes seen flying with sandhill cranes along the Platte River south of Kearney on 19 April 1980 were not observed on the river itself. Little information is available for the 4 May 1950 sighting of one crane near the Platte River at Overton; it is not known if the bird actually used the river.

Characteristics of the Platte River at each location known to have been used by whooping cranes are presented in Appendix D. Although the sample size is small, it is apparent that the birds prefer to roost in a wide river channel which has low, exposed, bare sandbars, relatively shallow water, slow rates of flow, and isolation from human disturbance. Feeding sites are usually within 4.8 km (3 miles) of the river. Habitat requirements are described in more detail in following sections.

Migration Corridor

It is possible to delineate the primary migration corridor of whooping cranes through Nebraska by plotting all of the confirmed sightings in the State during the last 30 years and drawing straight lines to enclose from 70-100% of them at each latitude (see Bellrose 1972). The resultant corridor through Nebraska is 160-192 km (100-120 miles) wide and angles 15 degrees west of north (Fig. 13). The eastern edge of the corridor intersects the northern border of the state at 98 degrees 45' longitude and the southern border at 98 degrees 15' longitude. The western edge intersects the northern border at 101degrees 00' longitude and the southern border at 100 degrees 30' longitude. Eighty-two percent of all confirmed, post-1949 sightings in Nebraska occur within the corridor; the remaining sightings are primarily to the west. Significant physiographic features within the corridor include the Niobrara River from 40 km (25 miles) west of Valentine to its confluence with the Keya Paha River; a portion of the sandhills; a substantial portion of the Calamus, North Loup, Middle Loup, and South Loup Rivers; a stretch of the Platte River from North Platte to Grand Island; the Rainwater Basin Area south of Kearney; and part of the Republican River.

Chronology of Migration

The chronology of spring and fall migration through Nebraska was well documented by Allen (1952); data from the past 29 years (1950-79) have shown a similar pattern.

Spring migration proceeds quite rapidly. Extreme dates for confirmed sightings are 10 March and 15 May; most cranes have been observed between 1 April and 20 April. In the past 29 years whooping cranes have been seen in Nebraska from 3 April through 4 May. Juveniles returning north with their parents have been seen from 14-19 April.

During fall migration, most are seen from 10 October through 1 November, with extreme dates of 22 September and 14 November. In the last 29 years, cranes have been observed in Nebraska from 3 October - 10 November. The first migrants to reach the state each fall are usually individuals or pairs without young. Family groups begin arriving around 16 October, and numbers of sightings peak from 22-27 October. Families have been seen in the state as late as 10 November.

Feeding Ecology

Whooping cranes forage in a variety of habitats. Fourteen upland and 10 wetland habitat types were represented among 120 feeding sites investigated along the migration route in the Great Plains (Table 6). Eighty-four percent of the sites were in upland habitats, and 80% of those involved agricultural lands. Fields containing emerging small grains or small grain stubble were the predominant agricultural habitats utilized. The use of wetland habitats for foraging was generally associated with sites in the vicinity of evening roosts.

Feeding sites in upland habitats were characterized by excellent horizontal visibility (usually an unobstructed view for at least 91 m (100 yards) in all directions and often an unobstructed view for several hundred meters in all directions), a lack of tall trees and dense shrubs immediately around the site, short vegetation on the site (often less than 30 cm high), little topographic relief (usually less than 9-12 m (30-40 feet) of relief, often less than 1.5-3.0 m (5-10 ft)), and gradual slopes (usually less than 7-9 degrees of slope, often less than 4-5 degrees). Feeding sites in wetland habitats were usually characterized by water less than 0.4-0.6 m (1.5-2.0 feet) deep, excellent horizontal and overhead visibility, and either very short or very sparse emergent vegetation.

Little is known about the specific food habits of the birds during migration although the habitats used by whooping cranes for feeding have been fairly well documented. Whooping cranes have been observed feeding on shoots of emerging winter wheat in Texas, Oklahoma, and Nebraska. Five cranes were seen feeding actively from fresh cow droppings in Oklahoma. The birds appeared to be eating heads of milo which had passed through the cattle relatively intact. Cranes have been seen eating waste milo in a recently harvested field in Texas. On several occasions in North Dakota, birds have been observed feeding on wheat from windrows and waste spills. Cranes have also been seen feeding on waste barley in North Dakota and waste corn in Nebraska.

The importance of animal foods in the diet of whooping cranes during migration is not known, but animal matter is known to constitute part of the diet. Swenk (1933) indicated cranes were "to be seen feeding in the lagoons on aquatic plants and animals, in the hay meadows or fields on insects, and, in the autumn, on the waste grains and insects in the wheat stubble fields." Prairie settlers in Nebraska recounted observations of whooping cranes feeding on the egg masses of frogs and . toads in buffalo wallows, and turning over cattle chips to obtain beetles (Allen 1952). In a shallow river where Allen observed cranes feeding, the only potential food items were small cyprinid, catastomid, and cyprinodontid fishes. Lahrman (1976) reported that fish were captured by whooping cranes at a site in Saskatchewan. J. Scrafford (pers. comm.) observed one of the adults of a family group capture, kill, and partially consume a large carp from a pond in the Rainwater Basin Area of south central Nebraska. The juvenile of the family also consumed a portion of the fish. The birds caught several more fish, frogs, and crayfish. Earthworms and salamanders also were thought to have been taken by these cranes. A farmer in North Dakota watched one whooping crane from a group of four kill a snake in a small grain stubble field and proceed to swallow it intact (T. Anderson, pers. comm.).

Although information on their food habits is limited, it is apparent that whooping cranes utilize both plant and animal foods during their migration through the midcontinent region. Although the proportions of plant and animal food in the diet are not known, it is probable that whooping cranes, like the sandhill cranes, require some animal matter to satisfy their nutritional needs. A major part of the whooping crane's energy requirements during migration across the Great Plains probably comes from waste agricultural crops.

Roost Sites

Shallow river channels represent one of several types of habitat used for roosting by whooping cranes. An evaluation of 10 documented whooping crane roosting sites on rivers identified the following characteristics as being present:

  1. wide channel, with 9 of 10 sites being between 155 and 365 m (170 and 400 yards);
  2. slow flow, i.e. approximately 0.4-1.8 ms-l (1-4 mph) although water in the main channel may be flowing faster;
  3. shallow water except in the main channel (all sites evaluated were <30 cm (12 inches) deep and six of nine sites were 5-15 cm (2-6 inches) deep);
  4. unvegetated;
  5. fine substrate, usually sand;
  6. good horizontal visibility unobstructed from river bank to river bank and at least a few hundred yards upstream and downstream (or to a bend in the river) at all sites;
  7. good overhead visibility without tall trees, tall and dense shrubbage or high banks near the roost;
  8. close proximity (usually <1.6 km or 1 mile) to suitable feeding sites;
  9. isolation (0.4 km or 0.25 mile) from roads, houses, and railroad tracks; and
  10. the presence of a certain type (described below) of sandbar near the middle of the river.
All roost sites evaluated had sandbars although the number and size varied among sites. Sandbars in the vicinity of the roosts usually sloped gradually into the water (often less than 1-2 degrees), had low topographic relief (often less than 0.3 m (1 foot)), no banks over several cm high, and had little or no vegetation.

Whooping cranes loaf on the sandbars and roost in the adjacent shallow, quiet water. Because of their position near the center of the river, these sandbars are apparently more secure from the approach of potential terrestrial and avian predators than are areas near the river's edge.

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