Subspecies and Populations:
A total of six sandhill crane subspecies have been identified in North America, including three migratory subspecies – Greater, Lesser and Canadian – and three nonmigratory subspecies – Mississippi, Florida and Cuban. The total population for all sandhill cranes is estimated at about 800,000. The Greater sandhill subspecies has made a significant comeback from the mid-20th century. In 1940 the estimated population was only 1,000; now biologists believe there are about 100,000.
For management purposes, the three migratory subspecies have been grouped into six populations that have relatively distinct distributions. Two populations occur in Colorado. The Rocky Mountain Population (RMP) is comprised entirely of Greater sandhill cranes, and numbers about 20,000. The Mid-Continent Population (MCP) is the largest North American population, numbering about 560,000, and is comprised of Lesser (primarily), Canadian and Greater subspecies.
Cranes are among the oldest living birds on the planet, with fossil records dating back 9 million years.
The sandhill crane is long-legged, long-necked bird. Its forehead is a vivid red, and the plumage is colored slate or brown-gray. Adults have a white chin, cheek and upper throat and black primaries. The young have a feathered head and chocolate-brown plumage with some rusty color. These cranes can be up to about four feet in length, have a wingspan of up to 7 feet, and weigh up to 11 pounds. During migration, they fly in V-formations or make long lines.
Their distinctive calls can be heard for miles. They have an unforgettably loud trumpeting call of gar-oo-oo. It is produced by a modified windpipe that has been likened to a French horn. In the grain fields of the San Luis Valley, the birds engage in an intriguing "dance" during which they jump up and down. The motion is believed to be a show of affection for their mates, and a show of aggression toward other birds that are getting too close.
Range: RMP sandhill cranes breed in Idaho, Utah, western Montana and Wyoming, and northwest Colorado and winter in New Mexico and northern Mexico. Virtually the entire RMP stops over in the San Luis Valley each year during spring (mid-February through March) and fall (late September through October) migration. The MCP breeds from northwest Minnesota and western Quebec, northwest through Canada, Alaska and Siberia, and winters in Oklahoma, New Mexico, Arizona, Texas and Mexico. The eastern plains of Colorado mark the western edge of the spring and fall migration corridor for MCP sandhill cranes; a small number (5,000-7,000) of MCP cranes also mix with RMP cranes in the San Luis Valley.
Habitat: Breeding birds are found in parks with grassy hummocks and watercourses, beaver ponds and natural ponds lined with willows or aspens. They nest in wetlands and shallow marshes. Sandhill cranes feed in mudflats around reservoirs, moist meadows and agricultural areas. During migration and winter, sandhill cranes regularly feed in dry fields, returning to water at night.
In the San Luis Valley, these majestic birds are attracted to vast wetlands and to the large grain fields. They spend about a month in the valley, mid-February to mid-March, resting and fueling up for the trip to their summer nesting grounds.
Diet: The birds are omnivorous. They forage for roots and starchy swellings that are found on the roots of tubers. They also eat seeds, small mammals and reptiles, eggs of other birds and invertebrates, such as worms, clams, insects and crayfish. Their bills are especially adapted for foraging and wetland hunting. The sturdy bill can penetrate frozen ground, and the serrated edges help the bird to snag slippery prey such as worms and snakes. Sandhill cranes are well-adapted to take advantage of high-carbohydrate agricultural foods, such as the unharvested barley, wheat and small potatoes that remain in fields in the San Luis Valley.
Reproduction: Sandhill cranes have an unusual and spectacular mating dance. They are very territorial during the breeding season. The typical number of young produced by a female is two eggs, which are usually laid on a huge mound of marsh plants yanked up by their roots. Nest construction can take up to seven days, and the nests may be five to six feet across.
The pair of cranes, both the male and female, shares incubation. Two chicks (also called colts) hatch two to three days apart, and the older one is often aggressive to its sibling. The parents keep the youngsters separated by walking apart; each adult is followed by one of the chicks. Full adult plumage is reached after two and a half years.
Status: In Colorado the Greater sandhill crane is listed as a species of special concern, with a focus of RMP Greater sandhill cranes that breed in the state. As people have moved into prime habitat areas, much of the nesting habitat became unsuitable because of either direct or indirect human disturbance during the incubation and chick-rearing periods, resulting in nest abandonment and loss of young.
There is currently no hunting season in Colorado for RMP sandhill cranes, but hunting seasons for RMP cranes are established in all other states in the range. Hunting seasons are established in Colorado for MCP sandhill cranes (east of the Continental Divide, excluding Jackson County and the San Luis Valley), and MCP cranes are harvested in most other states and provinces where they occur.