Grus americana
whooping crane

Grus americana is a native migratory bird species within the Nearctic region. The historical breeding range extends throughout the central United States and Canada and also used to include parts of north central Mexico. Few wild populations occur today. One population breeds within the Wood Buffalo National Park in the Northwest Territories of Canada and overwinters along the Gulf Coast in the Aransas National Wildlife Refuge of Texas. A second, minute population spends the summer in Idaho, Wyoming and Montana, and migrates to their wintering grounds in the Rio Grande Valley of New Mexico. A third introduced, non-migratory population resides in the Kissimmee Prairie, Florida.

Migration for the Wood Buffalo and Rocky Mountain populations includes stopovers throughout the United States and Canada including North Dakota, South Dakota, Kansas, Nebraska, Oklahoma, Montana, and Saskatchewan. (Allen, 1952; Armbruster, 1990; Doughty, 1989; Hayes, et al., 2007; Hughes, 2008; Johnsgard, 1983; Kuyt, 1993; Lewis, 1995)

The habitat of Grus americana, especially for nesting, consists of an open area which is close to large amounts of water and vegetation. The open area is especially important to visually detect possible predators. Whooping cranes nest in wetland and marsh areas or close to shallow ponds or lakes. Bulrush (Scirpus validus) marshes and diatom ponds are common and bogs are avoided. The habitats chosen typically include willow, sedge meadows, mudflats, and bulrush and cattail (Typha latifolia) marshes. These habitat types not only provide protection for predators but also provide a variety of food opportunities. During migration, Grus americana seeks similar habitats in wetlands, submerged sandbars and agricultural fields. In the winter, wet habitats are also sought out in the form of brackish bays and coastal marshes. Grus americana prefers marshes with a typical pH range of 7.6 to 8.3.

The elevation varies considerably due to the wintering and breeding ranges for Grus americana. The Aransas National Wildlife Refuge on the Gulf Coast of Mexico is at low elevations between 0 to 10 m. The northern breeding grounds in the Wood Buffalo National Park can reach elevations of up to 945 m. ("Elevation Map Texas Gulf Coast", 2008; Armbruster, 1990; Hughes, 2008; Lewis, 1995; Timoney, 1999; Timoney, et al., 1997; United Nations Environment Programme-Wo, 2008)

Adult whooping cranes are large, long-legged birds with long necks that measure 130 to 160 cm in length, and feature a wingspan of 200 to 230 cm. They are primarily white in color. Their primary wing feathers and long legs are black, while their toes are grayish-rose in color. The crown, lores, and malar areas are bare skin that varies in color from bright red to black. The bare skin is covered in short, black bristles that are the most dense around the edges of bare skin. They feature yellow eyes and a bill that is pinkish at the base, but mostly gray or olive in color. Both sexes resemble each other, however, the male whooping crane weighs more. Adult males and adult females weigh an average of 7.3 kg and 6.4 kg respectively. Young whooping crane chicks are cinnamon or brown in color along the back and a dull gray or brown on the underbelly. Juvenile whooping cranes have feather-covered heads and white plumage which is blotched cinnamon or brown. The area of the crown which becomes bare skin has short feathers.

Closely related sandhill cranes are gray and smaller than whooping cranes but they may appear white, especially in the sun. In flight, wood storks resemble whooping cranes, but they feature black secondary as well as primary feathers, yellow feet, and a short neck that is bare, dark skin. ("Cranes", 2003; Hughes, 2008; Johnsgard, 1983; Lewis, 1995)

Grus americana is a monogamous species and forms pairs around two or three years old. A pair bond develops through a variety of courtship behaviors including unison walks, unison calls, and courtship dances. Courtship usually begins with dancing, which starts with bowing, hopping, and wing flapping by one, and then both individuals. Each crane repeatedly leaps into the air on stiff legs, which continues until both individuals leap a few times in sync with each other. During the courtship dance the male may also jump over the female as she bows her head toward her body. Calling in unison is also important in pair maintenance and involves a duet between the female and male. The male has a lower call and positions the head straight up and behind vertical while the female is completely vertical or forward of vertical. Once one of the individuals begins the call the other joins in.

Once paired, whooping cranes breed seasonally and start nesting at approximately four years of age. Prior to copulation either individual begins walking slowly, with their bill pointed up, and neck forward and fully extended. This individual releases a low growl and the other individual walks with the same style behind the first and calling with its bill up toward the sky. Copulation commonly occurs at daybreak, however it can occur during any time in the day. Nesting pairs generally mate for life, but one will find a new mate following the death of the other. (Allen, 1952; Hughes, 2008; Johnsgard, 1983; Lewis, 1995)

Whooping cranes reproduce once a year from late April to May. Males and females participate in building a flat, ground nest usually on a mound of vegetation surrounded by water. In periods of drought, nesting sites can become no longer suitable for use. Typically two eggs are laid and the incubation period is 30 to 35 days. The sex ratio is nearly equal between the number of males and females hatched. The abandonment or loss of a nest is rare but breeding pairs can re-nest if either occurs within the first fifteen days of incubation. Fledging occurs between 80 to 100 days but the young remain with their parents until they reach independence at 9 months of age. Parents continue to feed and care for the fledgelings. Sexual maturity is reached between 4 and 5 years old. (Hughes, 2008; Kuyt, 1980; Lewis, 1995; Spalding, et al., 2009)

Both the male and female share equally in incubation responsibilities. The individual not incubating guards the nest from predators. Once hatched, young chicks are brooded by their parents at night or during bad weather. When a chick displays hunger, referred to as food begging, the parents provide them with food. The female provides the food more often than the male. The adult grasps the food in its bill and the chicks peck at the food. Food choices are initially worms and insects and grow is size as the chick develops. The young gradually start to feed independently. Food begging can be seen in young birds six to nine months old. The majority of juvenile birds completely leave their parents at the end of spring migration the following year. (Hughes, 2008; Lewis, 1995)

The estimated longevity of wild Grus americana is 22 to over 30 years. In captivity, the birds are expected to live up to 35 to 40 years old. The mortality of whooping cranes in their first year is approximately 27%. The survival rate of females for their first year is 55% the survival rate of males. Diseases, such as avian tuberculosis and avian cholera, are possible mortality causes for whooping cranes. A cause of mortality of some captive chicks has been intestinal coccidia parasites. Coccidia parasites have been found in both captive and wild whooping cranes and is transmitted through feces. These parasites include Eimeria gruis and E. reichenowi. Coccidiosis is less likely to occur in wild populations due to the large territory and small brood size of whooping cranes. Drought during the breeding season results in greater mortality of the young, since they have to travel farther for food resources and are at risk of attack by terrestrial predators. (Forrester, et al., 1978; Lewis, 1995)

Whooping cranes are diurnal and roost on the ground at night. Historically, Grus americana is a migratory species, but only two out of the three extant wild populations are migratory. Members of Grus americana live primarily in breeding pairs or small family groupings. They are able to move around primarily through walking or flying. During flight, whooping cranes can flap, soar or glide and the use of each is dependent on the nature of flight. Soaring and gliding are more important for long migratory flights. While walking, whooping cranes exhibit head-bobbing behavior. Swimming is generally seen in young chicks. Whooping cranes also have distraction and threat displays to intimidate and ward of predators. (Cronin, et al., 2005; Cronin, et al., 2007; Johnsgard, 1983; Lewis, 1995)

Territory size averages 4.1 square km in size and males are the main defenders of this territory. (Kuyt, 1993; Lewis, 1995)

The key form of communication for Grus americana, as indicated by their common name, the whooping crane, is vocal communication. Many calls have been identified for this species including: contact calls, stress calls, distress calls, food-begging calls, flight-intention calls, alarm calls, hissing, flight calls, guard calls, location calls, precopulation calls, unison calls, and nesting calls. Territory defense is linked with the unison and guard calls. Unison calls are also important in pair formation. The calls of whooping cranes are important as they serve in deterring predators, warnings of attack, protecting and caring for the young, and locating other individuals within the species.

Like all birds, whooping cranes perceive their environment through visual, auditory, tactile, and chemical stimuli. (Cronin, et al., 2005; Cronin, et al., 2007; Lewis, 1995)

Grus americana is omnivorous and eats a variety of plant and animal material both on the ground and in water. The primary wintering foods are blue crabs (Callinectes sapidus) and wolfberry fruits (Lycium carolinianum). Other wintering foods include: clams, acorns, snails, grass hoppers, mice, voles and, snakes. On migratory stopovers through the central United States and Saskatchewan, whooping cranes feed on plant tubers and waste grains in agricultural fields. While on breeding grounds their diet consists of minnows, insects, frogs, snakes, mice, berries, crayfish, calms and snails.

Within whooping crane's winter diets blue crabs provide the highest crude protein value and wolfberries have the highest metabolic energy and lipid content. (Butzler and Davis, 2006; Hughes, 2008; Lewis, 1995; Nelson, et al., 1996)

Whooping cranes are the most vulnerable in the first year and especially up until fledging. Dry years make the young particularly vulnerable as the nests are easily accessible to terrestrial predators.

Whooping cranes have a number of strategies for preventing attacks such as alarm calls or a distraction display for large predators. The most common display is a slow walk strut, with the body turned sideways to the predator and the feet lifted high. This emphasizes the crane's large size and may deter an attack. If the predator persists, a whooping crane lowers its bill to the ground and releases a low growl. As a final warning before a physical attack, a crane will face the predator, and spread and droop its wings while extending its neck. When a large predator nears the nest, the incubating parent may leave the nest to lure the predator away by dragging its wing in a distraction display.

Whooping cranes are subject to predation from both terrestrial and aerial predators. Some common terrestrial predators include black bear, wolverines, gray wolves, red foxes, lynx, bobcats, coyotes, and raccoons. Bald eagles, northern ravens, and golden eagles are all aerial predators of cranes. Golden eagles have been reported to attack whooping cranes in the air and are a significant threat during migration. Whooping cranes fly at very high altitudes during migration, which may be a strategy to avoid these fatal aerial attacks. (Cole, et al., 2009; Ellis, et al., 1999; Hughes, 2008; Lewis, 1995)

Whooping cranes are both predators and prey to a number of species. As omnivores, these birds impact many populations within local ecosystems. Currently with such low population numbers, this species likely cannot support a predator species, but historically it may have played a larger role as prey.

Whooping cranes serve as an important model for the positive effects of wildlife conservation and management. It is a valuable symbol of conservation and international co-operation between governments for many people. Thousands of people visit the wintering site, Aransas National Wildlife Refuge, each year in order to see whooping cranes. (Armbruster, 1990; Hayes, et al., 2007; Lewis, 1995)

There are no adverse effects of whooping cranes on humans.

Whooping cranes have been the center of many conservation projects. Even though they are still endangered, they have recovered from levels of near extinction in the 1940's to 1950's. Whooping cranes had a total population of 21 in the winter of 1954 and had approximately 260 individuals in 2009. There are a number of ways in which recovery of whooping cranes has been promoted. This includes protection through laws such as, the United States Migratory Bird Act. There are also intense captive breeding and re-introduction efforts. In some cases eggs produced by captive pairs are cared for by human caretakers dressed as whooping cranes, also known as costume-rearing. These re-introduced birds have experienced problems with migration, and it is presumed that juvenile birds learn migration routes from their parents. To help these birds, small, white planes are used as "parent" birds that guide the juveniles on their first journey to their wintering grounds. These methods have had mixed success, but the population is increasing overall. ("Birds Protected by the Migratory Bird Treaty Act", 2009; Cole, et al., 2009; Doughty, 1989; Urbanek, et al., 2010)

The genus Grus is comprised of ten crane species which is divided into four subgroups. Whooping cranes belong to the subgroup "the Group of Five" which also includes Eurasian cranes (Grus grus), hooded cranes (G. monacha), black-necked cranes (G. nigricollis) and red-crowned cranes (G. japonensis). ("Cranes", 2003; Doughty, 1989)