What is a Whooping Crane

Whooping crane (Grus americana):

Photo by Karen Willes, all rights reserved

General Information:

The whooping crane occurs only in North America and is North America’s tallest bird, with males approaching 1.5 m (5 ft) when standing erect. The whooping crane adult plumage is snowy white except for black primaries, black or grayish alula (specialized feathers attached to the upper leading end of the wing), sparse black bristly feathers on the carmine crown and malar region (side of the head from the bill to the angle of the jaw), and a dark gray-black wedge-shaped patch on the nape. The common name “whooping crane” probably originated from the loud, single-note vocalization given repeatedly by the birds when they are alarmed. Whooping cranes are a long-lived species; current estimates suggest a maximum longevity in the wild of at least 30 years. Whooping cranes currently exist in the wild at 3 locations and in captivity at 12 sites.

The July 2010 total wild population was estimated at 383. There is only one self-sustaining wild population, the Aransas-Wood Buffalo National Park population, which nests in Wood Buffalo National Park and adjacent areas in Canada, and winters in coastal marshes in Texas at Aransas. In addition, there is a small captive-raised, non-migratory population in central Florida, and a small migratory population of individuals introduced beginning in 2001 that migrate between Wisconsin and Florida in an eastern migratory population. The last remaining wild bird in the reintroduced Rocky Mountain Population died in the spring of 2002. The captive population contained 152 birds in July, 2010, with annual production from the Calgary Zoo, International Crane Foundation, Patuxent Wildlife Research Center, Audubon Species Survival Center, and the San Antonio Zoo. The total population of wild and captive whooping cranes in July, 2010, was 535.

The species historical range included Alabama, Arkansas, Colorado, Florida, Georgia, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia, West Virginia, Wisconsin, Wyoming. See below for information about where the species is known or believed to occur.

Reference: US-FWS ECOS Website

Taxonomy: The whooping crane is in the Family Gruidae, Order Gruiformes (Krajewski 1989, Meine and Archibald 1996). The closest taxonomic relatives in continental North America are 5 races of sandhill crane (G. canadensis): the lesser (G. c. canadensis); Canadian (G. c. rowani); greater (G. c. tabida); Florida (G. c. pratensis); and Mississippi (G. c. pulla) (the last also listed as endangered by the USFWS (Meine and Archibald 1996).

Habitat Requirements: The whooping crane breeds, migrates, winters, and forages in a variety of habitats, including coastal marshes and estuaries, inland marshes, lakes, ponds, wet meadows and rivers, and agricultural fields.

Photo by Karen Willes, all rights reserved

Breeding Ecology:  Whooping cranes may start nesting, defined as laying eggs, as early as 3 years of age (Kuyt and Goossen 1987, Brian Johns, CWS, pers. comm.). However the average age of first egg production is 5 years (Kuyt and Goossen 1987). From the results of color-banding studies in the AWBP, 3-year-old whooping cranes have been documented nesting 10 times (5 males and 5 females), including one instance where both members of the pair were 3 years old (Kuyt and Goossen 1987, Brian Johns, CWS, pers. comm.). In the FP, 3-year-olds have nested on 4 occasions, including 1 pair with both cranes that were 3-years-old. The first two nesting attempts documented for the EMP included one female that was 3-years-old and a pair with both cranes that were 3-years-old. Pair formation can occur rapidly or be a lengthy process. Bishop (1984) observed pair bonds that developed over 1 to 3 winters from associations in subadult flocks on the wintering grounds. Stehn (1997) observed that 27.7{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be} of pair bonds formed during spring migration or on the breeding grounds without any prior association at Aransas. Bishop and Blankinship (1982) documented several instances in which 2- and 3-year-old color-banded birds paired with unmarked birds. Whooping cranes are monogamous, but will re-pair, sometimes within only a few days, following the death of their mate (Blankinship 1976, Stehn 1992c, 1997).

Experienced pairs arrive at WBNP in late April and begin nest construction. They show considerable fidelity to their breeding territories, and normally nest in the same general vicinity each year. Several pairs have nested in the same areas for 22 consecutive years. These nesting territories, termed “composite nesting areas”, vary considerably in size, ranging from about 1.3 to 47.1 km2 (0.8 to 29 mi2 ) but averaging 4.1 km2 (2.5 mi2 ) (Kuyt 1976a, 1976b, 1981a, 1993a). Adjoining pairs usually nest at least 1 km (0.6 mi) apart; however, nests have been recorded as close as 400 m (435 yds) from each other (Brian Johns, CWS, pers. comm.). From the initiation of egg laying until chicks are a few months of age, the activities of pairs and family groups are restricted to the breeding territory. Whooping Crane Recovery Plan 2006 6 Eggs are normally laid in late April to mid-May, and hatching occurs about 1 month later. The incubation period is from 29 to 31 days (Kuyt 1982). Kuyt (1995) reported that “Among 514 clutches observed between 1966 and 1991, 454 (90.8{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be}) contained 2 eggs, 43 (8.6{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be}) only 1 egg, and 3 (0.6{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be}) 3 eggs.” Eggs are light brown or olive-buff overlaid with dark, purplish-brown blotches concentrated primarily at the blunt end. Eggs average 100 mm in length and 63 mm in width (Bent 1926, Allen 1952, Stephenson and Smart 1972, Kuyt 1995). Whooping cranes may re-nest if their first clutch is destroyed or lost before mid-incubation (Erickson and Derrickson 1981, Kuyt 1981b, Derrickson and Carpenter 1982). However, egg predation is uncommon, and re-nesting by whooping cranes has only been documented a few times (Kuyt 1981b). Whooping cranes generally nest annually, but may skip a season when nesting habitat conditions are unsuitable, if they are nutritionally stressed (Chavez-Ramirez et al. 1997, Johns 1998b), or for other (not apparent) reasons. In 2005, 12 out of 70 known adult pairs (17.1{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be}) failed to nest in WBNP. Whooping cranes usually produce clutches of 2 eggs laid 48-60 hours apart. Incubation begins with the first egg laid, resulting in asynchronous hatching of the eggs. This asynchrony may follow the insurance hypothesis, as discussed by Forbes and Mock (2000), where parents add marginal offspring to their clutch/brood as a hedge against early failure of core brood members. Hatching asynchrony may be an adaptation to the availability of food resources or a means of ensuring that the adults do not expend an inordinate amount of time attending to 2 young if they are in marginal habitat. In whooping cranes, eggs laid after incubation has begun usually only produce fledged young if the earlier laid egg fails to hatch or the chick dies soon after hatching. Not attempting to breed in a particular year may be a time and energy saving adaptation to prepare for a future breeding season (Stenning 1996). Erickson (1975) noted that although whooping cranes may lay 2 eggs, only about 10{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be} of families arriving on the winter range have 2 chicks. About 90{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be} of nests therefore contain 1 egg that is unlikely to result in a fledged chick. However, the second egg plays an unknown role in providing insurance that at least one chick survives. Boyce et al. (2005) suggest that removal of the second egg could actually increase the likelihood that one chick fledges. In nests with 2 eggs, the first hatched has the greater chance of survival in the wild. Habitat conditions, including food availability and predator abundance, affect survival. In years with suitable habitat conditions crane pairs may raise 2 young (Johns 1998a). For example, during the 1958-59 winter, 8 of the 9 young that arrived at Aransas were from twin pairs. In 1997 and 1998, at least 9{3f72e8ded4d47acce7842a60e006ced52f5015bd23a49866b41b0e3eb0f030be} of second hatched whooping crane young survived to fledging age (Bergeson et al. 2001a). During the years from 1938-l964, prior to egg-removal at WBNP, 101 single chicks and 15 pairs of “twin” siblings arrived at Aransas NWR from 230 nests or 213 2-egg clutches (Kuyt 1987). “Twins” arrived in 9 of the 29 years. No pairs brought 2 juveniles during the egg-pickup years 1965-1996 even though a few nests were left with 2 eggs in most years. Between 1997-2004, with no egg pickup, 8 pairs successfully raised twin chicks to fledging age (Brian Johns, CWS, pers. comm.), however only 4 pairs brought twin chicks to Aransas NWR (Tom Stehn, ANWR, pers. comm.). Whooping crane parents share incubation and brood-rearing duties. Except for brief intervals, 1 member of the pair remains on the nest at all times. Females tend to incubate at night (Allen 1952, Walkinshaw 1965, 1973) and take the primary role in feeding and caring for the young (Blankinship 1976). Chicks are capable of swimming shortly after hatching; however, parents Whooping Crane Recovery Plan 2006 7 and young return to the nest each night during the first 3-4 days after hatching. Later, parents brood their young wherever they are at night or during foul weather. During the first 20 days after hatching, families generally remain within 1.8 km of the nest site (Ernie Kuyt, pers. comm.) with daily movements averaging 340 m (Doug Bergeson, pers. comm.). Information on marked individuals suggests that most juveniles and subadults spend the summer near their natal area (Kuyt 1979b, 1981a). Sexually immature birds (up to 4-year-olds) spend the summer as singles, pairs or in small groups of 3 to 5 birds. These birds usually occur on the peripheries of territories of nesting pairs.

A Whooping crane chick is in the process of working its way out of the egg.

Juvenile Plumage: The juvenile plumage is a reddish cinnamon color. At age 80-100 days, the chick is capable of sustained flight. At age 120 days, white feathers begin to appear on the neck and back. Juvenile plumage is replaced through the winter months. The plumage is predominantly white by the following spring and the dark red crown, lores (area between eye and bill), and malar areas are apparent. Rusty juvenile plumage remains only on the head, the upper neck, secondary wing coverts (smaller feathers covering middle of wing), and scapulars (wing feathers arising from the shoulder) (Stephenson 1971). Yearlings achieve typically adult plumage late in their second summer.

Migratory Behavior: As spring approaches, “dancing” behavior (running, leaping and bowing, unison calling, and flying) increases in frequency, and is indicative of pre-migratory restlessness (Allen 1952, Blankinship 1976, Stehn 1992b). Family groups and pairs are usually among the first to depart wintering grounds, often assisted by seasonal strong southeast winds. First departure dates are normally between March 25 and April 15, with the last birds usually leaving by May 1. Occasional stragglers may linger into mid-May, and in 19 years, between 1938-2005, 1 to 4 birds (34 birds total) have remained at ANWR throughout the summer. Some of these birds were ill or crippled or mates of birds that were crippled.

The spring migration is usually completed in 2-4 weeks, more rapidly than the reverse trip in the fall, as there is no known spring staging area. Parents separate from their young of the previous year upon departure from ANWR, in northward migration while in route to the breeding grounds or soon after arrival on the breeding grounds (Allen 1952, Stehn 1992a, B. Johns, CWS, pers. comm.). Autumn migration normally begins in mid-September, with most birds arriving on the wintering grounds between late October and mid-November. Occasionally, stragglers may not arrive until late December. Whooping cranes migrate south as singles, pairs, in family groups, or as small flocks of 3 to 5 birds (Johns 1992). They are diurnal migrants and make regular stops to feed and rest. Large groups of up to 20 sometimes use the same stopover location. Pairs with young are among the last to leave the breeding range (Allen 1952, Archibald et al. 1976, Stephen 1979). The migration corridor (Fig. 2) was determined by mapping confirmed sightings reported by individuals (Stephen 1979, Johnson and Temple 1980, Austin and Richert 2001) and radiotracking whooping cranes during the period 1981-1984 (Kuyt 1992). Their first stop often occurs in northeast Alberta or northwest Saskatchewan, about 500 km southeast of their departure area in WBNP. Local weather conditions influence distance and direction of travel, but whooping cranes generally are capable of reaching the autumn staging grounds in the northcentral portion of the Saskatchewan agricultural area on the second day of migration. Most of the cranes remain for 2 to 4 weeks in the large triangle between Regina, Swift Current, and Meadow Lake, where they feed on waste grain in barley and wheat stubble fields and roost in the many wetlands (Johns 1992). The remainder of the migration from Saskatchewan to the wintering grounds is usually rapid, probably weather-induced, and may be completed in a week (Kuyt 1992).

Winter Ecology: For almost half of the year, whooping cranes occupy winter areas on and adjacent to ANWR. Although close association with other whooping cranes is tolerated at times on the wintering Whooping Crane Recovery Plan 2006 8 grounds, pairs and family groups typically occupy and defend relatively discrete territories. Studies indicate a declining territory size as the population increases, with territories averaging 117 ha (Stehn and Johnson 1987). Limited expansion of the wintering area has occurred (Tom Stehn, pers. comm.). Subadult and unpaired adult whooping cranes form small flocks and use areas outside occupied territories (Blankinship 1976, Bishop and Blankinship 1982). Subadults tend to winter near the territories where they spent their first year (Bishop 1984). Paired cranes will often locate their first winter territory near the winter territory of one of their parents (Bishop 1984, Stehn and Johnson 1987).

Diet: Whooping cranes are omnivorous (Walkinshaw 1973), probing the soil subsurface with their bills and taking foods from the soil surface or vegetation. Young chicks are fed by their parents. They gradually become more independent in their feeding until they separate from the parents preceding the next breeding season. Summer foods include large nymphal or larval forms of insects, frogs, rodents, small birds, minnows, and berries (Allen 1956, Novakowski 1966, Bergeson et al. 2001b). Foods utilized during migration are poorly documented but include frogs, fish, plant tubers, crayfish, insects, and agricultural grains. The largest amount of time is spent feeding in harvested grain fields (Johns et al. 1997). The winter diet consists predominately of animal foods, especially blue crabs (Callinectes sapidus), clams (Tagelus plebius, Ensis minor, Rangia cuneata, Cyrtopleura costada, Phacoides

pectinata, Macoma constricta), and the plant wolfberry (Lycium carolinianum)(Allen 1952, Uhler and Locke 1970, Blankinship 1976 and 1987, Hunt and Slack 1987, Chavez-Ramirez 1996). Most foraging occurs in the brackish bays, marshes, and salt flats on the edge of the mainland and on barrier islands. Occasionally, cranes fly to upland sites when attracted by fresh water to drink or by foods such as acorns, snails, crayfish and insects, and then return to the marshes to roost (Hunt 1987, Chavez-Ramirez et al. 1995). Uplands are particularly attractive when partially

flooded by rainfall, burned to reduce plant cover or when food is less available in the salt flats and marshes (Bishop and Blankinship 1982). Some whooping cranes use upland sites frequently in most years, but agricultural croplands adjacent to ANWR are rarely visited. High fall tides and heavy rains sometimes flood tidal flats. In these circumstances, the birds forage almost exclusively on blue crabs and wolfberry in flooded areas. In December and January, tidal flats typically drain as a result of lower tides, and the birds move into shallow bays and channels to forage primarily on clams, a

Blue crab

lthough blue crabs are occasionally captured while probing the bottom. Clams are a significant dietary item when water depths are low, temperatures cold, and following drought when the blue crab population is low. Most clams and small blue crabs (5 cm or less in width) are swallowed whole. Larger crabs are pecked into pieces before being swallowed (Blankinship 1976). The AWBP whooping cranes spend their summers and winters in restricted locations. Therefore, their pressure on local invertebrate food species may cause depletions, especially of blue crabs at Aransas. However, the total whooping crane population is so small that it is unlikely to exert any ecological effects except in small areas.


Reference: US-FWS ECOS Recovery Plan