Signs of Spring 8: The Spring Sandhill Crane Migration!

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Sandhill crane. Photo by K. Thomas. Wikimedia Commons

Click on the following link to listen to an audio version of this blog … Sandhill crane spring migration

To really be able to visualize the Spring migration of our local population of western sandhill cranes (also called the “Rocky Mountain Sandhill Cranes”) one has to be able to visualize the river that is their guide and sustaining agent: The Rio Grande.

The Rio Grande is best known as the international boundary between Mexico and the southern Texas edge of the United States. The river runs nearly 1000 miles from El Paso to the Gulf of Mexico near Matamoras forming a barrier-moat between the U.S. and Mexico of varying widths and depths. Before the Rio Grande arrives in El Paso, though, it has already traveled 800 or 900 curving miles across the extensive, arid steppes and mountain valleys of Colorado and New Mexico generating along the way unique, riparian ecosystems (the “bosques”). This upper and middle part of the Rio Grande, the part before it becomes famous, if you will, is the part that influences the migration of the sandhill cranes and also a wide variety of other bird species.

Canby Mountain, Colorado. Photo by G. Sumer. Wikimedia Commons

The headwaters of the Rio Grande are in the San Luis Mountains of south-central Colorado. Two small streams flowing down from Canby Mountain converge and then pass almost due east through the San Luis Valley and its extensive grazing land and agricultural fields (barley, wheat, potatoes, lettuce). The river then takes an abrupt turn to the south following the Rio Grande Rift and travels in an almost straight north-south line down the length of New Mexico.

West of Taos, New Mexico the Rio Grande cuts a deep gorge (“The Rio Grande Gorge”) through the basaltic rocks of the Taos Plateau volcanic field. It then continues on in the Rio Grande Rift   accentuating the rift’s boundary between the North American Craton to the east and the Colorado Plateau to the west.  We’ve talked about the Rio Grande Rift before when we explored some of it ancient volcanoes near Albuquerque (see Signs of Spring 10, March 3, 2019).

Bosque on Rio Grande in New Mexico. Photo by Camerafiend. Wikimedia Commons

The bosques (derived from the Spanish tern for “woodland”) stand out sharply against the surrounding, brown, sagebrush steppes. They are single canopy woodlands dominated by mesquite, cottonwood, desert willow and desert olive. Under the trees is a dense shrub layer that includes desert hackberry. blue palo verde, graythorn, Mexican elder and Virgin’s bower. A botanical study of a bosque near Albuquerque found that it housed 150 species of plants. The bosques are rich, diverse ecosystems that flourish adjacent to the hot, harsh, water-starved steppes.

The vegetation of the bosque helps to generate shade and moderate water loss from both vegetation and underlying soils. The shade also provides significant relief in the summer from the intense sunlight and high daytime temperatures. Many animals occupy the bosque to take advantage of its more moderate microclimate. Desert cottontails, racoons, American beaver, long-tailed weasels, bobcats, mountain lions and coyotes are all found abundantly with the bosques.

Coopers hawk (in my backyard). Photo by D. Sillman

Migratory birds (including sandhill cranes, ducks, geese, herons, egrets, numerous warblers) and a rich community of raptors (including northern harriers, red-tailed hawks, sharp-shinned hawks, Cooper’s hawks and American kestrels) are also found in the bosques especially  in the winter. There are also many bird species in the bosques year-round where they find safe, sometimes unique breeding habitats. Some breeding species of importance include the black-chinned hummingbird, the summer tanager, the gray catbird, the yellow breasted chat and the black-headed grosbeak. The Corrales Bosque Preserve just north of Albuquerque, had the highest density of nesting Cooper’s hawks in North America.

Over 250 bird species have been identified from the Corrales Bosque Preserve alone. Although these bosque woodlands make up less than 1% of the landscapes in New Mexico, at certain times of the year they provide habitat for more bird species than all of the other types of habitats in the state combined.

So the bosques are a nearly continuous line of rich, often moist habitats that stretch all the way from Texas into the heart of southern Colorado. They are the sustaining highway for the migrating sandhill cranes.

Sandhill crane. Photo by Mwanner. Wikimedia Commons

Sandhill cranes (Antigone canadensis) are one two species of cranes found in North America. The other is the extremely endangered whooping crane ( Grus americana ). Cranes are the tallest of the flying birds with most of the world’s fifteen species having individuals that reach four-and-a-half to over five and a half feet in height. The sandhill crane stands four foot six and has a wingspan of six and a half to seven feet! It has long legs, a long neck and can weigh up to eleven pounds! A very substantial bird!

I wrote about sandhill cranes a couple of years ago and went into some detail as to why the sandhill cranes have been able to stay so abundant while the whooping cranes have become so perilously  endangered (see Signs of Winter 13, February 25, 2021). Both species eat similar foods (they are broadly omnivorous eating everything from roots, seeds, small mammals, reptiles, worms, clams, insects and crayfish) and both species have extremely effective bills that can grab prey and even dig into frozen ground while searching for food. Two big differences between these two type of cranes, though, that may account for the difference in their population survivals are reproductive potential (sandhill cranes can have two eggs in a clutch while whooping cranes only have one egg in their clutches) and the broader habitat selection and habitat tolerance of the sandhills.

Sandhill cranes have a bright red forehead and slate-gray to brown-gray body feathers. Their legs are black and their wing feathers droop at the rear of their body producing a distinctive “bustle”. Cranes are among the oldest living birds on Earth. Fossils of cranes have been dated back to over nine million years.

Whooping crane with Sandhill cranes. Photo by USFWS, Public Domain

Colorado, for most sandhill cranes, is a seasonal staging site, a place to rest before heading on to their more northern breeding sites or before coming back to their southern, over-wintering sites. Increasingly, though, as the overall size of the Rocky Mountain Population of the sandhills has increased, more and more sandhill cranes are staying in Colorado to breed. Breeding groups can be found in Grand, Jackson, Moffat, Routt and Rio Blanco Counties, and over the past two decades smaller breeding groups have been observed in Mesa, Montrose, Delta and, most recently, Gunnison Counties.

Breeding pairs of sandhill cranes scatter themselves out near water (beaver ponds, reservoirs, streams, lakes, wetlands and marshes). They rely on the dense cover of the surrounding vegetation and their blending  plumage for concealment and safety.  They nest on the ground and during the breeding season are, in spite of the great size, quite inconspicuous.

At other times of the year, though, sandhill cranes can gather in very large numbers especially in their southern, over-wintering areas and in “staging areas” along their migratory flyways. These staging areas are very important sites for rest and refueling during both their Spring and Fall migrations. For the Rocky Mountain sandhills, their primary overwintering location is the Bosque de Apache in southern New Mexico. There are three main, migratory staging areas in Colorado:    on the Yampa River near Hayden, on the Elk River west of Steamboat Springs, and in the agricultural fields and wetlands of the San Luis Valley in the southcentral part of the state.

Sandhill cranes in Monte Vista, Colorado (San Luis Valley). Photo by D. Soldara, Flickr

Up  to 20,000 sandhill cranes gather in the San Luis Valley from mid-February to mid-March creating a spectacular, natural display. The flocks then return in the Fall (from mid-October to late November) accompanied by the juveniles (“colts”) from the summer breeding season. The Fall gathering is less concentrated and, seemingly, less coordinated than the Spring. In the Fall, the sandhills seem to be more focused on getting back to their over-wintering ranges as quickly as possible and gather and linger in the staging areas in smaller groups and for much shorter periods of time.

Deborah and I were not able to get down to the San Luis Valley this Spring to see the staging-gathering of the sandhills. We hope to go down this Fall to see them passing through on their way to southern New Mexico. We will also be up in Steamboat Springs this summer and will keep out eyes open for local sandhills on the Elk and Yampa Rivers.