Northern Prairie Wildlife Research Center
The apparent migration path in the United States, as outlined by the distribution of whooping crane observations, is very similar to that delineated earlier in Armbruster (1990) and the Whooping Crane Recovery Plan (U.S. Fish and Wildlife Service 1994), following a relatively straight line north-northwest from Aransas NWR to central North Dakota then curving northwest along the Missouri Coteau to the North Dakota-Saskatchewan border (Figure 1). Examination of locations relative to ecoregion on individual state maps (See State Summaries) shows that most observations were in Great Plains or Glaciated Plains ecoregions. During migration, cranes appear to associate with river systems, particularly the Missouri River in the Dakotas, but closer examination of the plots for each state and habitat data indicates only rarely were cranes actually observed on a river, except in Nebraska. Spring and fall observations were relatively similar in their overall pattern (Figures 2 and 3), except for higher frequency observations in fall on Quivira NWR, Cheyenne Bottoms SWA, Salt Plains NWR, and in Texas. See maps in State Summaries for more detailed depiction of spring and fall distributions.
Three confirmed observations were not included in the observation database because they were outside the main flyway, but their locations are noteworthy. On 11 November 1998, 1 whooping crane was observed flying 8 km north of Waukegan at Illinois Beach State Park, Lake County, Illinois. Six whooping cranes were observed during 9-12 April 1999 in Harrison County, Iowa. On these same dates, a family of 3 whooping cranes were sighted in Page County, Iowa.
We plotted the distribution of observations for 4 time periods: 1) 1943-74 (Figure 4), 2) 1975-83 (Figure 5), 3) 1984-91 (Figure 6), and 4) 1992-99 (Figure 7). The first time period corresponds to sightings collected before observational efforts increased. The general pattern of migration appears to have changed little over the 57 years of observations. Very few observations were recorded in Texas during the first time period. Observations around Cheyenne Bottoms SWA and Quivira NWR increased in later periods.
We examined the frequency of observations for 3 of the 4 areas designated as critical habitat for whooping cranes: Cheyenne Bottoms SWA, Salt Plains NWR, and Quivira NWR. We did not summarize the frequency of observations for the reach of the Platte River designated as critical habitat because we did not have clear geographic boundaries for that area, but it is obvious from the Nebraska map that whooping cranes were frequently observed in this area. Whooping cranes have been observed frequently on the other 3 critical habitat areas, primarily during the fall, during the past 43 years and also during the 25 years corresponding to the site evaluation program (Table 3). Only on Quivira NWR have cranes been frequently sighted in spring. A number of other named areas also occurred frequently in the sightings database: Rainwater Basin, Nebraska; Lostwood NWR, North Dakota; and Divide County, North Dakota. Additional observations likely occurred in the Rainwater Basin but were not so named in the site description; we also lacked clear geographic boundaries to examine that area in greater detail. These numbers cannot serve as definitive evidence of frequency of use because of the inconsistencies in how site descriptions were recorded (i.e., whether the formal name of an area was used). Examination of the maps can better indicate those regions where whooping cranes were frequently sighted.
|Table 3. Frequency (%) of whooping crane sightings at named locations during 1943-99 (57 years) and 1977-99 (25 years), corresponding to the site evaluation program.|
|Cheyenne Bottoms SWA, KS||5||75||8||68|
|Salt Plains NWR, OK||14||51||2||84|
|Quivira NWR, KS||28||49||56||88|
|Rainwater Basin, NE||21||19||32||16|
|Lostwood NWR, ND||21||21||48||44|
|Divide Co, ND||17||9||24||2|
Information on first departure dates of individual cranes from Aransas NWR indicated spring migration commenced as early as 7 March and as late as 4 April and was quite variable among years (W. Jobman, unpublished data for 1975-99). Based on incidental observations, spring migration appeared to commence in mid- to late March and continue through mid-late May (Figure 8). Extreme dates included a few observations in Oklahoma, Nebraska, and Kansas in February and early March, and in South and North Dakota in June. Some of these outliers were cranes that overwintered in Oklahoma or summered in North Dakota; a few dates for additional observations in North Dakota after 15 June were considered "summer" and were not included because these were not considered migrants. Only 4 records were available for Colorado (range 28 Feb to 20 May).
The peak of migration, as indicated by median dates of occurrence, was 8 April in Texas, 6 April in Oklahoma, 12 April in Kansas and Nebraska, 19 April in South and North Dakota, and 26 April in Montana. Few whooping cranes were observed in the United States after early May. The main periods of occurrence in each state over all years seem to be relatively short: the core 50% of the observations, as represented by the shaded box (25th to 75th percentiles), ranged from 6 days in Texas to 13 days in South Dakota.
Fall migrants were first observed in North and South Dakota in early September; in Nebraska, Kansas, and Oklahoma in early October; and in Texas by mid-October. The peak of migration, as indicated by median dates, were 22 October in Montana, 18 October in North Dakota, 22 October in South Dakota, 27 October in Nebraska, 27 October in Kansas, 28 October in Oklahoma, and 1 November in Texas. The main periods of occurrence in each state for all years were somewhat longer in fall than in spring: the core 50% of the observations, as represented by the shaded box (25th to 75th percentiles), ranged from 10 days in Nebraska to 22 days in North Dakota. The latest observations of fall migrants occurred in Kansas, Oklahoma, and Texas in December; a few of these observations included cranes that ultimately overwintered away from Aransas NWR (data for "winter" period not included here). Two records occurred in western Minnesota (11 and 21 Oct), 2 in western Missouri (13 Oct and 1 Nov), and 1 in Colorado (28 Oct). Fall arrival dates to Aransas NWR ranged from 25 September to as late as 29 October but generally occurred in mid-October (W. Jobman, unpublished data for 1975-99).
Examination of spring and fall migration chronology for each state indicated no apparent change in migration chronology over the 57 years of observations (1943-99) (See graphs for each state in State Summaries). Median dates of spring migration in Nebraska were quite consistent, varying ≤5 days since 1960. Indeed, median dates for both spring and fall for all states usually varied ≤10 days. Sample sizes were generally small (<10) before 1975 for all states. In Oklahoma, some observations of a marked crane that apparently overwintered in 1986-87 were considered "winter" and thus not included. Two very early spring observations in Oklahoma in 1995 probably were associated with 1 crane that apparently overwintered there for several years.
It is important to note that "use" in this report does not connote or imply habitat preference or selection. Whooping crane sightings records were not collected in a systematic fashion but were incidental observations. Because observations were a chance occurrence, patterns evident in the data must be considered with caution. We cannot assume these patterns are representative of actual habitat use or preferences.
The complete EVALDAT database included 1060 observations. We excluded 2 records (2 sub-observations under 1 main observation) of a single bird recorded in North Dakota in late August 1989 because it was a summer record. All other site evaluation records were for fall or spring.
The number of records were equally divided by season but varied by state (Table 4). Spring records of whooping cranes were more common than fall observations for Nebraska and Montana. In other states, fall records were more common. More than two-thirds of spring records were from Nebraska.
Multiple sub-observations: Multiple sub-observations occurred for 175 main observations (16.5% of the total data set; Table 5). Nebraska had the highest number of multiple sub-observations and also had more cases with >3 sub-observations than other states. In all states, multiple sub-observations often included >1 record for a each site use. When multiple sub-observations and records were excluded, sample sizes for habitat assessments by site use were: FEEDEVAL, n =306; ROSTEVAL, n =141; and DUALEVAL, n =248.
|Table 4. Distribution of site evaluations among states, overall and by season, and percent of total season observations occurring in each state, 1977-99.|
|* excludes 1 summer record|
|Table 5. Number of situations in which there were multiple sub-observations for a single main observation, by state, 1977-99.|
|State||No. sub-observations/main observation|
|* Nebraska: 7, 8, 8, 10, 11, 15|
Overall: Single family groups included all combinations of 1-2 adults and 1-2 juveniles. Most groups observed had 1-3 cranes, although some had as many as 14 cranes in spring and 19 cranes in fall (Figure 9). Mixed groups in spring included as many as 14 (13 with 1 juvenile), and in fall included as many as 19 (18 adults with 1 juvenile).
Roost Sites: In spring, pairs were most commonly observed at roost sites, followed by single families. Few mixed groups were observed in spring, and only 2 single juveniles were sighted (Figure 10). In fall, single families, pairs, and adult groups were equally common, but few mixed groups or single adults were sighted and no single juveniles were sighted. Single adults were more commonly observed in spring than in fall. In both seasons, adults with juveniles occurred more commonly in single families than in the larger mixed groups.
Feeding: Observations of pairs, adult groups, and single families were most common in spring and fall at feeding sites (Figure 10). Single adults were somewhat more common in fall than in spring. Seven single juveniles were sighted in spring.
Dual-use Sites: Adult groups, single families, and pairs were again the most commonly observed social groups at dual-use sites (Figure 10). Four single juveniles were observed in spring. Maximum group sizes were similar to those noted above for roosting or feeding sites.
All Records: Palustrine wetlands were the most commonly recorded wetland system used by whooping cranes (68.8%); riverine wetlands accounted for 21.6% and lacustrine wetlands 9.6% of site evaluation records (n = 644). However, these percentages are dominated by records from Nebraska, which comprised 50.2% of all records for which we were able to discern wetland system. Only 11 (7.9%) of the 139 riverine records were from outside of Nebraska: Kansas River, Kansas; Popular River, Montana (2 records under 1 main observation); Missouri River (2 in MT, 3 in ND); Souris River, North Dakota (J. Clark Salyer NWR), and Arkansas River, Oklahoma (2 records under 1 main observation). The distribution of observations among wetland systems clearly differed between Nebraska and other states. In Nebraska, the proportions of observations occurring on palustrine and riverine systems were both high (56.0 and 39.6% of state records, respectively), whereas in other states palustrine records accounted for >75% of records. Only in Montana did the proportion of sightings (4 of 17, or 36%) rivers approach the proportion observed in Nebraska, but note that the total number of observations were low. See State Summaries for details specific to each state.
Roost Sites: Overall, palustrine (58.2%) and riverine (33.3%) wetlands were the predominant wetland systems recorded for roosting cranes; only 11 (7.8%) records were on lacustrine wetlands (n = 141). Four roost sites were recorded as flooded cropland, including 1 site also described as winter wheat stubble and 1 as milo stubble. All of these latter sites were classified as emergent wetlands with seasonal (2) and temporary (2) water regimes. One site in Gray County, Kansas, was described as a tailwater pit. Another site described as flooded cropland had no wetland system recorded.
All but 1 of the 47 records of riverine roosts were from Nebraska; the other record was from the Missouri River in Montana. In Nebraska, 59.0% of roosts were observed on riverine wetlands, 37.2% on palustrine, and 3.8% on lacustrine wetlands. In Montana, the riverine record was 1 of only 2 roost observations; the other record was for a palustrine wetland. In the remaining states, palustrine records account for 71-100% ( = 85.5%) of roost sites and lacustrine wetlands for 12.9% of roost sites. No roost sites were described as flooded pasture, wooded creek or draw, or as upland types.
Single families and pairs each comprised >30% of observations on palustrine wetlands; relatively few mixed groups or single cranes were observed (Figure 11). On riverine wetlands, pairs and single adults were most common; family groups (single families [13%] and mixed groups [2%]) were relatively uncommon. Cranes observed on lacustrine wetlands were mostly family groups (54.5% vs. 27.3% nonfamily groups and 18.2% singles). Cranes on palustrine wetlands were somewhat more evenly split between family (42.5%) and nonfamily groups (55.0%), with only 2 singles observed (2.5%). On riverine wetlands, 56.5% were nonfamily groups, 28.3% were single cranes, and 15.2% were families. All single adults were recorded on rivers in spring.
When all states are examined together, use of wetland systems differed by season (Figure 12). Spring-migrant cranes were observed with similar frequency on palustrine and riverine wetlands but only occasionally on lacustrine wetlands, whereas fall-migrant cranes were observed primarily on palustrine wetlands and were infrequently observed on lacustrine and riverine wetlands. These seasonal patterns are largely driven by the large number of observations of cranes in Nebraska on the Platte, Niobrara, Middle Loup, and North Loup rivers in spring. In Nebraska alone, riverine sites accounted for 78% of roost site records in spring, and no roosts were noted on lacustrine wetlands; in fall, half of the records were of riverine wetlands, and 11% were on lacustrine wetlands (Figure 13). For all other states, there was no seasonal difference; palustrine sites accounted for >75% of roost records.
Feeding Sites: Most (239 of 306) feeding site records occurred on non-wetland (upland) sites. Where feeding cranes were observed on wetlands (n =67), palustrine (86.6%) wetlands were the predominant system used; only 7 (10.4%) records were on riverine wetlands and 2 (3.0%) were on lacustrine systems (Calamus Reservoir, NE, and Lake Sakakawea, ND). Palustrine wetlands used for feeding were primarily recorded in Nebraska (49.1%) and North Dakota (23.7%); there were ≤6 palustrine records for each of the other states (n = 68). Of the 7 riverine records, 4 occurred in fall and 3 in spring. In fall, cranes were observed feeding on the Souris River in North Dakota (J. Clark Salyer NWR), and on the South Loup River, North Platte River, and Birdwood Creek (Lincoln County) in Nebraska. In spring, cranes were observed feeding on the Middle Loup, Platte, and Niobrara rivers. No sites were described as wooded creek or draw; 4 were described as flooded pasture, and 1 as tailwater pit (6 adults and 1 juvenile, Mead County, KS, in spring). No differences were apparent between seasons (Figure 12).
Only 2 states had sufficient observations to consider differences among wetland systems within that state. In North Dakota, 87.5% of wetland feeding sites were palustrine, 6.3% were lacustrine, and 6.3% were riverine (n = 16). In Nebraska, 80.6% of wetland feeding sites were palustrine, 16.6% were riverine, and 2.8% were lacustrine (n = 36).
Adult groups, pairs, and single families each comprised about 25% of cranes observed on palustrine wetlands; relatively few mixed groups and only 1 single juvenile were observed (Figure 11). Only pairs, groups of adults, and 1 single adult were observed feeding on riverine wetlands. Only 2 records of feeding occurred on lacustrine wetlands (1 single family, 1 single adult).
Dual-use Sites: Palustrine systems (71.0%) again were the predominant wetland systems used by cranes for both roosting and feeding; use of lacustrine and riverine wetlands were similar (10.9 and 14.1%, respectively; n = 248). Of the 176 palustrine records for dual-use sites, 34.7% were in Nebraska, 30.7% in Kansas, 16.5% in North Dakota, 10.2% in South Dakota, and 5.7% in Oklahoma; there were <5 (<2%) records for each of Montana and Texas. Of the 35 riverine records, 31 (88.6%) were in Nebraska, with 1 record each (all occurring in fall) in Kansas, Montana, North Dakota, and Oklahoma. Use of lacustrine systems varied somewhat among states: 35.7% in North Dakota, 25.0% in South Dakota, 14.3% in Nebraska, 14.3% in Oklahoma, and 10.7% in Kansas (n = 28). No sites were described as flooded pasture or wooded draw. Two were described as tailwater pit (Mead County, KS, and Sedgewick County, KS). Fourteen records were described as flooded cropland. One of the 14 had further description codes denoting marsh and oat stubble/green rye, 1 as seasonally flooded basin, and 2 as winter wheat. See State Summaries for details of named rivers and lakes or reservoirs used.
At a state level, palustrine wetlands accounted for >67% of sites used for both roosting and feeding in all states. Lacustrine wetlands accounted for 25-28% of such records in North Dakota, Oklahoma, and South Dakota (see State Summaries for details).
Use of wetland systems differed somewhat by season (Figure 12). Spring migrants were primarily observed on palustrine systems, with proportionately fewer observations on riverine and lacustrine systems In fall, use of palustrine systems remained similar to that in spring but use of lacustrine systems was somewhat lower and use of riverine systems somewhat higher.
Single families, adult groups, and pairs each comprised 24-31% of cranes observed on palustrine wetlands (Figure 11). Cranes observed on lacustrine wetlands were largely single families and adult groups. Half of the 10 observations on upland sites were of adult groups. We noted little difference in the distribution of nonfamilies and singles among wetland systems.
All records: Wetland class was defined as emergent wetlands (50.7% of all records), unconsolidated bottom (28.4%), aquatic bed (11.2%), and unconsolidated shore (9.3%); 2 (0.4%) were defined as streambed (2 sub-observations for a pair foraging in disked cornfield along unvegetated streambed; Kearney County, NE) (n = 493). No cranes were observed in wetland classes defined as rocky bottom, rocky shore, forested wetland, or moss-lichen. Records from Nebraska comprised 61.4% of the data for this variable.
Roost Sites: Cranes most often were observed roosting on unconsolidated bottom (primarily palustrine wetlands) and palustrine emergent wetlands (Table 6). No seasonal differences in wetland classes were apparent.
Feeding Sites: Where cranes were observed feeding on wetlands, they largely occurred on palustrine emergent wetlands (Table 6). Use of wetland classes differed between spring and fall. Use of unconsolidated bottom sites was lower in spring (3.2%  than in fall (21.7% ), and use of emergent sites was higher in spring than in fall (87.1%  to 60.9% , respectively).
Dual-use sites: Wetlands with emergents (palustrine wetlands only) or unconsolidated bottoms were the most common wetland classes used by cranes for both feeding and roosting (Table 6). Differences in use of wetland classes between seasons was slight, with a tendency for greater use of aquatic-bed wetlands in fall and unconsolidated-shore wetlands in spring.
|Table 6. Percent of wetland observations defined as having unconsolidated bottom, aquatic bed, unconsolidated shore, or emergent vegetation relative to wetland system, by site use, 1977-99. (Pal = Palustrine, Lac = Lacustrine, Riv = Riverine)|
|Wetland class||Roost sites
(N = 108)
(N = 52)
(N = 180)
Roost Sites: Seasonal and semipermanent water regimes were most commonly used by roosting cranes (Figure 14), although in lacustrine systems, 6 of 11 sites were classified as having permanent water regimes. Use of wetland regimes for roosting differed seasonally among permanent, seasonal, semipermanent, and temporarily flooded regimes. Spring migrants were largely observed roosting on seasonal and semipermanent regimes (43.1 and 39.7%, respectively), with lesser use of permanent (6.9%) and temporary (6.1%) wetlands. Observations of roosting fall migrants were more equally distributed among water regimes (25.0% permanent, 32.5% seasonal, 17.5% semipermanent, and 25.0% temporary).
Feeding Sites: Feeding cranes used mostly seasonal, semipermanent, and temporary wetlands (Figure 14). We noted no seasonal differences among permanent, seasonal, semipermanent, and temporary regimes.
Dual-use Sites: Dual-use sites most commonly were seasonal and semipermanent wetlands in both spring and fall (Figure 14). Occurrence at dual-use sites did not vary seasonally among permanent, semipermanent, seasonal, and temporary wetlands, although there was a trend toward higher use of permanent wetlands in fall than in spring.
Roost Sites: Roosting cranes were commonly observed on large (>40 ha) wetlands; frequency of occurrence on these larger wetlands was higher in fall than in spring (59% vs. 27%; Figure 15). Closer examination of the records indicated that the frequent use of large wetlands is affected by wetland system and, in fall, by frequent observation of cranes on large, managed wetlands within 3 public conservation areas. Nine of the 10 lacustrine sites were >40 ha and the other site was >20 ha; most of these sites were reservoirs or human-altered lakes. Fall lacustrine roost sites included Lovewell Reservoir, Kansas; Harlan County Reservoir, Duck Lake (Cherry County), and Lake Maloney, Nebraska; Pocasse NWR and Stone Lake SWA, South Dakota; and Lake Sakakawea, North Dakota. Spring roost sites included Kirwin NWR and Glen Elder Reservoir, Kansas (2 records). In palustrine systems, wetlands >40 ha accounted for 43% of all records (n = 77). Observations of roosting cranes on the large wetland management units and reservoirs on Salt Plains NWR, Quivira NWR, and Cheyenne Bottoms SWA accounted for 27 (35%) of the 78 records overall, and for 24 (92%) of the 26 records in fall. When we excluded these 3 areas and Funk Waterfowl Production Area (WPA), which also has large managed wetlands and frequently hosted whooping cranes in fall, we found a more even distribution of palustrine wetland sizes used in both spring and fall (Figure 16).
The composition of social groups differed somewhat among the 3 pooled wetland size classes (Figure 17). All observed mixed groups (n = 7) occurred only on wetlands >20 ha, but groups of adults were relatively uncommon on these larger wetlands. Single families and pairs comprised the largest proportion of cranes observed on large wetlands.
Feeding Sites: Wetlands on which cranes fed were smaller than those used for roosting or for dual use (Figure 15). Feeding cranes were more frequently observed on wetlands <2.5 ha in spring than fall, but occurrence of other wetland sizes were similar between seasons.
The composition of social groups on feeding sites showed greater differences among 3 wetland size classes (Figure 17) than on sites used for roosting or dual use. Groups of adults were least commonly observed and single families most commonly observed feeding on large (>20 ha) wetlands. As noted for roost sites, single families and pairs comprised the largest proportion of cranes observed on large wetlands.
Dual-use Sites: Similar to roost sites, cranes were commonly observed both roosting and feeding on larger wetlands than were feeding cranes, and cranes were more frequently observed on wetlands >40 ha in fall than in spring (Figure 15). Use of these large wetlands again was primarily due to frequent observations of cranes on the management units and reservoirs of Quivira NWR (9 of 20 records in spring, 26 of 64 records in fall), Cheyenne Bottoms SWA (1 record in spring, 5 in fall), and Salt Plains NWR (9 records in fall). Lakes and reservoirs accounted for many of the other sites >40 ha in fall, but in spring the other sites were large palustrine wetlands on WPAs or private lands. When we examined only palustrine wetlands and excluded the 4 management areas noted above, we found that cranes occurred on a wider variety of wetland sizes, particularly in spring and, in fall, >30% of the sites were wetlands >40 ha (Figure 16).
There were relatively minor differences in occurrence of social groups on the 3 pooled wetland size classes (n = 179) (Figure 17).
All Data: River width was recorded at 117 (84%) of the 139 riverine sites; 109 (93%) of these 117 records (93%) were for sites in Nebraska. Widths ranged from 36 to 457 m and averaged 227 ± 88 (SD) m.
Roost Sites: Widths of rivers at roost sites ranged from 76 to 457 m and averaged 233 ± 84 m (n = 44). Seasonal differences in river width were suggested, with slightly wider river sites used in spring (247 ± 86; n =31) than in fall (200 ± 74; n = 13). Occurrence of larger rivers in spring are primarily due to predominance of the Platte River in spring observations (83.3% of spring riverine observations having a width measurement); in fall, smaller rivers such as the Middle Loup, North Loup, and Niobrara rivers accounted for 7 of the 13 records for river width.
Feeding Sites: We had data on river width for only 4 riverine sites used for feeding, all in Nebraska (crane pair on Birdwood Creek, Lincoln County in fall; 3 cranes on Middle Loup River in spring; pair on Platte River in spring; and 4 cranes on Niobrara River in spring). These ranged from 36 (Birdwood Creek) to 274 m wide and averaged 173 ± 100 m.
Dual-use Sites: Widths of rivers used for both roosting and feeding ranged from 91 to 411 m and averaged 229 ± 82 m (n =28). River width did not vary by season.
All Data: Maximum depths of wetlands on which cranes were observed ranged from 3 to 305 cm and averaged 51 ± 41 cm (SD) (n = 297). Cranes were observed on shallower wetlands in spring (46 ± 32 cm; n = 161) than in fall (56 ± 50 cm; n = 136). Specific sites within wetlands where cranes were observed feeding or roosting averaged 18 ± 11 cm (range 3-61 cm; n = 196).
Roost Sites: Maximum depths of wetlands used for roosting ranged from 8 to 305 cm and averaged 67 ± 54 cm (n = 69). Wetlands used for roosting in spring (65 ± 35 cm; n = 40) were similar in depth to those used in fall (69 ± 72 cm; n =29). Depths at specific roost sites within the wetland ranged from 5 to 46 cm and averaged 20 ± 9 cm (n =41).
Feeding Sites: Maximum depths of wetlands used for feeding ranged from 3 to 107 cm and averaged 31 + 25 cm (n = 31). Wetlands used for feeding in spring (24 + 13 cm; n = 19) were somewhat shallower than those used in fall (44 ± 10 cm; n = 12). Depths at specific sites where cranes had been observed feeding ranged from 3 to 30 cm and averaged 12 ± 7 cm (n = 14).
Dual-use Sites: Maximum depths of wetlands used for both roosting and feeding ranged from 3 to 28 cm and averaged 50 ± 39 cm (n = 116). Wetlands used by cranes tended to be shallower in spring (44 ± 32 cm; n = 56) than in fall (56 ± 43 cm; n = 60). Depths at specific sites ranged from 3 to 61 cm and averaged 18 ± 12 cm (n = 80).
Roost Sites: Overall, 53.1% of roost sites were described as clear, 33.1% turbid, and 13.8% saline (n = 129). Water quality of roost sites clearly varied by wetland system (Figure 18). Most turbid wetlands were palustrine, although 3 river sites (Niobrara River, Brown County, NE; 2 sites on Platte River near Doniphan, NE) and 7 lakes also were classified as turbid. All sites described as saline were on Salt Plains NWR or Quivira NWR (often Big Salt Marsh), except for 1 site on Stone Lake SWA, South Dakota.
Feeding Sites: Overall, 59.3% of feeding sites were described as clear, 37.0% turbid, and 3.7% saline (n = 58). The majority of the 46 palustrine sites had clear water, however, data for lacustrine and riverine were sparse (Figure 18). Saline sites were located on Loucks WPA, North Dakota, and Quivira NWR, Kansas.
Dual-use Sites: Of the 211 dual-use sites with information, 42.2% were defined as clear, 39.3% turbid, and 18.5% saline. Water quality of dual-use sites clearly varied by wetland system (Figure 18). Most riverine systems had clear waters whereas a high proportion of lacustrine systems were turbid. Most saline sites were on Salt Plains NWR or Quivira NWR, although there were a number of smaller saline wetlands in North and South Dakota, Kansas, and Nebraska.
Roost Sites: Most wetlands used for roosting had soft substrates (38.5% sand, 52.6% soft mud), 7.4% had hard mud substrates, and 1.5% had other substrate types (n = 135). Substrates were closely associated with wetland systems: 95.7% of riverine wetlands (n = 46) had sand substrates, 80.3% of palustrine wetlands (n = 77) had soft mud substrates, and 6 (63.6%) of the 11 lacustrine wetlands had soft mud substrates. Hard mud substrates occurred in lacustrine (n = 3) and palustrine wetlands (n = 7).
Feeding Sites: Most (62.1%) wetlands used for feeding had soft mud substrates; 13.8% had sand, 13.8% had hard mud, and 10.3% had other substrates. Substrate again was closely related to wetland system: 65.2% of palustrine wetlands (n =46) had soft mud substrates, and 4 of 6 riverine systems had sand substrates. The 1 lacustrine system had soft mud.
Dual-use Sites: Most sites used for both roosting and feeding had soft substrates (23.2% sand, 63.9% soft mud); 8.9% had hard mud, and 4.0% had other substrates. Substrate was closely associated with wetland system: 91.2% of riverine wetlands (n = 34) had sand substrates, 75.9% of palustrine systems (n = 158) had soft mud substrates, and 58.3% of lacustrine systems (n = 25) had soft mud substrates and 29.2% had sand substrates. Hard mud substrates occurred in lacustrine (n = 2) and palustrine systems (n = 18).
Roost Sites: Most (78.7%) shorelines of roost sites were classified as having a slight slope (1-<5% slope); 18.5% were classified as having no slope (<1%), and 2.8% had 5-10% slope (n = 108). The latter included 1 roost site on the Niobrara River (Rock County, NE) and 2 stock ponds (Furnas County, NE; Jackson County, SD).
Feeding Sites: Most (70.7%) wetland shorelines of feeding sites had a slight slope (1-<5% slope); 17.1% had no slope (<1%), 9.8% had 5-10% slopes (seasonal wetland in McLean County, ND; Stone Lake [seasonal wetland], SD; and 1 marsh in Sully County, ND), and 1 (2.4%) had >10% slope (<6-ha marsh near Gibbon, NE) (n = 41). Nearly all of these records were for palustrine systems. Slope was recorded for only 1 lacustrine system (pool at Cheyenne Bottoms SWA) and 2 riverine sites (Platte River and Birdwood Creek, NE).
Dual-use Sites: Most (65.4%) wetland shorelines of dual-use sites had a slight slope (1-<5% slope); 23.5% were classified as having no slope (<1%), 6.2% had 5B10% slope, and 4.9% had >10% slope (n = 162). All 23 riverine sites, 68.4% of lacustrine sites, and 58.3% of palustrine systems at dual-use sites were classified as having 1-<5% slope.
Roost Sites: In riverine systems, roosting cranes more often were observed on unvegetated sites than on vegetated sites, but in palustrine sites they were observed on sites having a broad range of emergent vegetation types (Table 7). Emergent vegetation characteristics of lacustrine sites were intermediate between those of palustrine and riverine sites. Where vegetation did occur on riverine sites, it usually consisted of grasses or "other" (likely willow [Salix]).
Feeding Sites: In riverine systems, feeding cranes primarily were observed on unvegetated wetlands, but they also were observed on sites with some rush, smartweed, or other vegetation (likely willow) (Table 7). Palustrine sites used for feeding had a broader range of emergent vegetation types. One of the "other" categories was described as corn, which is inappropriate as an emergent vegetation for wetlands.
Dual-use Sites: Emergent vegetation on dual-use sites varied among wetland systems used (Table 7). In riverine wetlands, cranes rarely used sites with any vegetation. Palustrine wetlands had a variety of vegetation types. One of the "other" categories was further described as corn. Lacustrine systems used for both roosting and feeding tended to be unvegetated or vegetated with cattail or rush.
|Table 7. Frequency (%) of emergent vegetation types, by wetland system and site use. Percentages within a column do not sum to 100% for a wetland system within a site use because more than 1 type often was recorded per site. (Pal = Palustrine, Lac = Lacustrine, Riv = Riverine)|
|Vegetation type||Roost sites||Feeding sites||Dual-use sites|
Roost Sites: At roost sites, distribution patterns of emergent vegetation varied by wetland system (Figure 19). Although most riverine sites had no vegetation, as noted above, palustrine sites often had scattered vegetation. Palustrine sites having clumped or choked vegetation had a variety of vegetation types, with no single type dominating.
Feeding Sites: Distribution patterns of emergent vegetation at feeding sites varied by wetland system (Figure 19). Although most riverine sites had no vegetation, as noted above, palustrine feeding sites often had scattered or choked vegetation. No vegetation type dominated at palustrine sites relative to the distribution pattern of vegetation.
Dual-use Sites: Distribution patterns of emergent vegetation at dual-use sites varied by wetland system (Figure 19). Most riverine sites had no vegetation, as noted above, lacustrine sites were evenly split between no vegetation and scattered vegetation, and palustrine sites had a mix of patterns. No vegetation type dominated at palustrine sites.
All Data: Most sites where cranes were observed feeding were in upland crops whereas cranes observed at dual-use sites were more often in wetlands (see below). Seasonally-flooded habitat was largely comprised of flooded pasture (47% of records) and seasonal wetlands (42% of records). Permanent wetlands were largely marshes (30-40%) and reservoirs (30-40%). Sixty percent of upland cover was described as pasture. For upland crops, wheat comprised 83% of small grain stubble, corn comprised about 75% of row-crop stubble, and winter wheat comprised 80% of green crops.
Feeding Sites: Most sites where cranes were observed feeding were upland crops, with lower occurrence of cranes seen in seasonally flooded habitats, permanent water, or upland perennial cover. No cranes were recorded feeding in woodland (Figure 20). Proportions of habitat types varied little between seasons. Although upland crops occurred in similar high proportions in descriptions of both feeding sites and adjacent habitat, it is apparent that cranes were less frequently observed in upland cover or on wetlands than occurred in adjacent habitat (see below) (Figure 21).
There was little difference in the proportions of social groups observed feeding on permanent wetlands, cropland, and upland cover (Figure 22). In seasonal wetlands, groups of adults comprised 40% of cranes observed, with fewer pairs than in other habitat types. Single families tended to comprise a higher proportion of feeding cranes in cropland and upland cover than in wetlands. When we considered pooled social groups, we found no apparent difference in the distribution of family, nonfamily, and single groups among feeding habitat types.
In spring, cranes most frequently were observed feeding on row-crop stubble, with lesser use of small grain stubble and green crops; <10% of records were for standing small grain, standing row-crops and other (Figure 23). In fall, cranes were most frequently observed on green crops, small-grain stubble, and row-crop stubble. Cranes were infrequently observed in standing small grain, small-grain or row-crop stubble, or in other habitats such as CRP.
Dual-use Sites: Most dual-use sites were permanently or seasonally flooded wetlands, with lesser use of upland crops; no cranes were recorded feeding in woodland (Figure 20). Use of seasonal wetlands for both feeding and roosting was somewhat higher in spring whereas use of permanent wetlands and upland crop were higher in fall. Cranes were observed feeding in wetlands more frequently and in upland crops less frequently than occurred in adjacent habitat (see below) (Figure 21).
Similar to feeding sites, groups of adults observed on dual-use sites comprised a larger proportion of cranes observed on seasonal wetlands than on other habitat types. Pairs were the most commonly observed group on cropland and least commonly observed group on seasonal wetlands (Figure 22). When we considered pooled social groups, we found no apparent difference in the distribution of nonfamily, family, and single groups among feeding habitat types.
For spring dual-use sites, cranes were observed with similar frequency on green crops, small-grain stubble, and row-crop stubble but were not observed on other crop types (Figure 23). For fall dual-use sites, proportions of crane observations were similar between small-grain stubble and greens crops, with lower frequency of row-crop stubble, and infrequent occurrence on standing row crops and other cropland habitat.
Roost Sites: Habitats adjacent to roost sites (<1.6 km) most frequently were described as cropland (73.8%) and upland perennial cover (69.5%); permanent wetlands (36.2%) and upland cover (30.5%) were also common. We then examined riverine and palustrine systems separately because we suspected the main river roost sites, used primarily in spring (and represented almost entirely by Nebraska records), would differ in occurrence of woodland habitat along the river perimeter. As anticipated, woodland habitat occurred adjacent to >70% of riverine roost sites but adjacent to <8% of palustrine roost sites (Figure 24). All riverine roosts also had adjacent upland cover, whereas only about half of palustrine roost sites had such adjacent cover; however, upland cropland was common. For both wetland systems, seasonal wetlands occurred more frequently in adjacent habitat for spring roost sites, probably reflecting their seasonal occurrence in the landscape, and permanent wetlands occurred more frequently adjacent to roost sites in fall. Upland cropland was more common in spring than in fall, but we caution that the large number of fall records from Cheyenne Bottoms SWA, Quivira NWR, and Salt Plains NWR, where habitat adjacent to roosts is more likely to be non-cropland habitat than on private lands, may be a factor in these seasonal differences.
Feeding Sites: The most common habitats adjacent to feeding sites were cropland and upland perennial cover; permanent and seasonal wetlands and woodland were less common nearby (Figure 21). Occurrences of seasonal wetlands and upland cover in adjacent habitat were higher in spring than in fall. The higher occurrence of woodland in spring likely relates to greater occurrence of feeding observations in spring on river systems, all of which occurred in Nebraska. Adjacent croplands were most likely to be green crops (winter wheat, alfalfa, winter rye, barley) or row-crop stubble (Figure 25).
Dual-use Sites: Habitats adjacent to dual-use sites were largely cropland, upland perennial cover, and permanent water areas, with lesser use of seasonally-flooded wetlands and woodland (Figure 21). Occurrence of seasonal wetlands nearby was higher in spring whereas occurrence of permanent wetlands was higher in fall. Upland cover and row-crop stubble were the most common adjacent crop types (Figure 25).
We examined similar habitat within 16 km for all records combined, regardless of site use, because distances between feeding and roost sites usually were much less than 16 km. Habitat similar to that of the evaluation site was categorized as moderately abundant (41.2%) to abundant (23.3%) within 16 km of the sites, and extent of similar habitat was low for 33.9% of sites (n = 561). Two sites (0.4%) had no similar habitat and 7 (1.2%) were recorded as unknown. Those sites recorded as having no similar habitat included 1 record on or near the Platte River southeast of Kearney, Nebraska (apparently considered a wetland but no data on system or regime) and 1 record in Sully County, South Dakota, which from other information appeared to be a flooded corn field (i.e., recorded as palustrine wetland and corn as the emergent vegetation).
Roost Sites: When all roost records were considered, we found no apparent pattern in distances between roost and feeding sites: 28.4% were <0.40 km, 23.0% were 0.40-0.79 km, 8.1% were 0.80-1.19 km, 16.2% were 1.20-1.6 km, and 24.3% were >1.6 km from roost sites (n = 74; percentages sum to >100 because of multiple distances given for a single roost site). However, distances obviously varied with wetland system (Figure 27). On palustrine roost sites, about two-thirds of feeding sites were <0.8 km from the roost, likely reflecting wetlands situated in cropland areas, whereas over half of riverine roost sites were >1.2 km from feeding sites. All riverine roosts which were >1.6 km from feeding sites occurred on the Platte River (1 in fall, 9 in spring). Roost sites on the Middle Loup and North Loup rivers were usually <0.8 km from feeding sites. All 5 of the lacustrine records, where distances to feeding sites were recorded, were >1.2 km from the roost.
Feeding Sites: Distances to feeding sites were recorded in 10 records; we assumed these refer to distance to other feeding sites. Five sites were <0.40 km, 1 was 0.40-0.79 km, 1 was 0.80-1.19 km, and 3 were >1.6 km from the first feeding site.
Dual-use Sites: A higher proportion of dual-use sites were within 0.40 km of other feeding sites than for sites used only for roosting: 49.2% of feeding sites were <0.40 km of the site, 13.3% 0.40-0.79 km, 8.6% 0.8-1.19 km, 8.6% 1.20-1.6 km, and 20.3% >1.6 km from the site (n = 128). Palustrine and lacustrine dual-use sites often were closer to feeding sites than riverine dual-use sites (Figure 26).
Feeding Sites: Grains and invertebrates were considered most commonly available at feeding sites, reflecting the high use of cropland sites (Table 8).
Dual-use Sites: Invertebrates were considered most commonly available at dual-use sites, with frogs, grains, fish, and tubers also common (Table 8). The diversity of potential foods reflects the mixture of wetland and upland habitat types in these data.
|Table 8. Frequency (%) of potential foods available at feeding and dual-use sites, 1977-99. Numbers within a column do not sum to 100% because more than 1 type was often recorded per site.|
|Potential food||Feeding sites||Dual-use sites|
|* Includes snakes.|
A total of 50 records noted actual foods observed being consumed by cranes; 23 records were for feeding sites (14 in spring, 9 in fall) and 27 records were for dual-use sites (11 in spring, 16 in fall). Thirty (60%) of the observations were from Nebraska. Cranes most often were observed consuming grain on both feeding (n = 20) and dual-use sites (n = 18) even though 76% of dual-use sites were palustrine wetlands. Other items observed consumed by cranes included fish (n = 4; in dual-use sites only), invertebrates (n = 3), mollusks (n = 2), snakes or other (n = 4), and salamander, tubers, and frogs (n = 1 each). Cranes were observed eating fish on 4 seasonal wetlands and 1 wetland of unknown regime.
More than two-thirds of sites where cranes were observed were <0.8 km of human developments (32.5% <0.4 km, 37.5% 0.4 - <0.8 km), 7.8% were 0.8 - <1.2 km away, 3.8% 1.2-1.6 km away, and 7.9% were >1.6 km away; 10.8% were classified as not applicable (n = 554, using 1 record for each main observation). We noted no apparent differences in distance to human development among roost, feeding, and dual-use sites.
Fifty-eight percent of cranes observed were >805 m from utility (power or phone) lines; 2.5% were observed <91 m away, 16.3% were 91-401 m away, and 22.4% were 402-805 m away (n = 362, using 1 record for each main observation). We noted no apparent differences in distance to utility lines among roost, feeding, and dual-use sites.
Roost Sites: Overall, nearly half (48.7%) of roost sites were classified as having visibility of 91-402 m, 28.2% had visibility <91 m, 6.9% 402-805 m, and 16.2% with >805 m or unlimited visibility (n = 117). Because of the potential influence of trees that are often closely associated with river edges, we separately examined visibility of roost sites by wetland system. Roost sites with greatest visibility distances were on palustrine and lacustrine areas, whereas riverine roost sites had the lowest visibility distances (Figure 27). No riverine roost sites were ranked as having visibility >800 m; visibility on these sites likely was limited by woody growth along the shoreline. We found no difference in the distribution of nonfamily, family, and single groups among visibility classes at roost sites.
Feeding Sites: Two-thirds of feeding sites (67.0%) were classified as having 91-402 m visibility, 10.7% <91 m, 10.1% 402-805 m, and 12.2% with >805 m or unlimited visibility (n = 197). Visibility distances were quite similar among palustrine, riverine, and upland habitats (Figure 27). The distribution of nonfamily, family, and single groups differed little among visibility classes for feeding sites.
Dual-use Sites: Visibility was <91 m for 21.9% of dual-use sites, 91-402 m for 37.7% of sites, 402-805 m for 7.7% of sites, and >805 m or unlimited visibility for 32.7% of sites (n = 183). Dual-use sites with greatest visibility distances were on uplands or palustrine wetlands, whereas riverine dual-use sites tended to have the lowest visibility distances (Figure 27). The distribution of nonfamily, family, and single groups differed little among visibility classes at dual-use sites.
Roost Sites: Roosting whooping cranes were associated with other bird species in 33.3% (47 of 141) records. They were most commonly associated with sandhill cranes (89.4%) but also were observed in association with American white pelicans (Pelicanus erythrothynchos; 6.4%) and geese (6.4%; included snow geese [Chen caerulescens] and Canada geese [Branta canadensis]). Spring associations with sandhill cranes were primarily on Platte River roost areas (24 of 32); 6 palustrine sites in the Rainwater Basin and other areas also were shared with sandhill cranes in spring. In fall, whooping cranes were observed with sandhill cranes on 6 palustrine sites (Quivira NWR and Funk WPA), 1 riverine site, and 4 lacustrine sites. Whooping cranes roosted with geese in 2 palustrine sites in Kansas and 1 in South Dakota.
Feeding Sites: Feeding whooping cranes were associated with other bird species in 31.7% of records (97 of 306). They most commonly were associated with sandhill cranes (94.8% of the 97 records) but also were observed in association with geese (4.1%; identified as snow geese, Canada geese, or simply geese), and with ducks, American white pelicans, swans (Cygnus spp.), and great blue herons (Ardea herodias) (1 record each). Spring associations with sandhill cranes (n = 49) were primarily on and around the Platte River (n = 26) and Rainwater Basin (n = 6), but in fall whooping cranes were found with sandhill cranes in a wide variety of areas. Whooping cranes were observed with geese in seasonally flooded basins and/or cropland on 2 sites in North Dakota (McLean and Divide counties), 1 in South Dakota (Pennington County), and 1 in Nebraska (Gleason WPA).
We compared habitat types for records where whooping cranes were feeding in association with sandhill cranes and those unassociated with sandhills cranes. Differences were not large, but suggested that whooping cranes associated with sandhill cranes had somewhat lower use of seasonally-flooded wetlands (14.3% vs. 21.5%) and upland cover (8.8% vs. 11.2%), higher use of permanent wetlands (15.0% vs. 9.9%), and higher use of cropland (82.4% vs. 71.5%) than whooping cranes not associated with sandhill cranes.
Dual-use Sites: Whooping cranes were associated with other bird species in 24.2% of dual-use site records (60 of 248). They were most commonly associated with sandhill cranes (85.0%) but also were observed in association with geese (8.3%; included snow geese and Canada geese), American white pelicans (6.5%), great blue herons (3.3%), ducks (3.3%), and swans (1.6%). Spring associations with sandhill cranes occurred on palustrine (n = 10), riverine (n = 6), and upland sites (n = 2). In fall, whooping cranes were most often found with sandhill cranes on palustrine sites (23) and occasionally on lacustrine (n = 3), riverine (n = 3), and upland (n = 2) sites. Whooping cranes were observed with white-fronted geese (Anser albifrons) at Medicine Lake NWR, Montana; Canada geese and snow geese in North Dakota (Lake Arena WPA and Divide Co.); and unspecified geese species in Nebraska (Gleason WPA).
We compared habitat types for dual-use site records associated with sandhill cranes and those unassociated with sandhill cranes. For dual-use sites, whooping cranes associated with sandhill cranes had lower use of seasonally flooded areas (17.6% vs. 35.6%) and permanent water areas (43.1% vs. 60.1%) but higher use of cropland (45.0% vs. 19.2%) than whooping cranes not associated with sandhill cranes; use of upland cover was similar (7.8% and 5.0%).
Private ownership accounted for >60% of sites used by whooping cranes, followed by federal ownership (Figure 28). More than 80% of feeding sites were on private land, reflecting the high use of crop fields. Federal ownership accounted for most ownership of roost sites. Seasonal differences were apparent but are probably due to the seasonal dominance of observations for some areas, such as the large number of observations on federal refuges in Kansas and Oklahoma in fall but not in spring.
A number of feeding site records indicated multiple ownership (e.g., federal and The Nature Conservancy, federal and private, federal and state). These were situations where the observed crane(s) moved from a tract of land under 1 ownership to a second under a different ownership (W. Jobman, personal communication). See State Summaries for details within each state.
Roost Sites: Most roost sites were considered secure, but nearly one-third were considered threatened. More than 90% of roost sites that were under federal or state ownership were considered secure whereas security of roosts on private lands was evenly split between secure and threatened (Figure 29). A higher proportion of roost sites in fall were considered secure than those used in spring (83 vs. 53%; n = 139); this likely is related to the more frequent sightings of cranes on national wildlife refuges in Kansas and Oklahoma in fall.
Feeding Sites: Few feeding sites were considered threatened, although most occurred on private lands (Figure 29). There were no seasonal differences in site security of feeding sites (94% in fall vs. 91% in spring; n = 301).
Dual-use Sites: Overall, >75% of sites used for both roosting and feeding were considered secure. Almost all federally-owned sites were considered secure but 28-32% of privately- and state-owned sites were considered threatened (Figure 29). A higher proportion of sites were considered secure in fall than in spring (82 vs. 69%; n = 242).
The corrected SAS database, which included all observation and site evaluation records, was exported to Excel, error-checked once again for identification number problems (minor details corrected), then imported to Access software. Data fields were grouped into tables on the basis of subject, and various tables and queries were created to automate data summarization. We developed a number of tables, grouping variables by subjects of likely interest, and created queries so that users could readily seek specific information. Tables developed included:
Over 50 specific queries were developed to allow users of the Access database to address specific questions of interest. The queries allow variables within each table to be summarized by desired variables, e.g,. by state, year, and/or season. Results are equivalent to those presented in this report but the queries allow users to examine the data for their particular state or for particular years of interest. This database is provided to the U.S. Fish and Wildlife Service and Nebraska Game and Parks Commission as part of this report.