Signs of Winter 13: Sandhill Cranes!

Photo by K. Thomas. Wikimedia Commons

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A few mornings ago while I was enjoying my second cup of coffee, the announcer on the radio reminded everyone of a coming, spectacular, natural event: in the next few weeks, 20,000 migrating sandhill cranes will be gathering in the lakes and wetlands of the Great Sand Dunes National Park in the San Luis Valley and also out on the Yampa and Elk Rivers just west of Steamboat Springs! They will hang out in the valley and around the rivers for about a month, feeding and resting up from the first leg of their spring migration, and then in mid to late March, disperse out to the north into their summer breeding grounds.

For the past month I have been looking for “Colorado Signs of Spring,” and here was a big one! I just needed to figure out where the San Luis Valley and Steamboat Springs were (my Colorado geographic sense is still in a very primitive state!). Then I had to figure out how to get there in a COVID-19-safe manner!

Sandhill cranes (Antigone canadensis) are one of 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 feet! A very substantial bird!

I’ve mentioned sandhill cranes several times over the years. I first saw them in the wetlands around Lubbock, Texas when I was an undergraduate student at Texas Tech, and  more recently we chased the “memory” of them up their spring migration route through New Mexico from the Bosque de Rio Grande through the banks of the Rio Grande in Albuquerque, just missing them each year (2014 and 2016)  we went out to New Mexico on our March Spring Break from Penn State.

But, finally, in August, 2017, while visiting Yellowstone, we matched up with the end of the cranes’ summer breeding period, and got see adults and fledglings (the “colts”) gamboling about in the isolated wetlands of the park. They were magnificent!  (see Signs of Fall 5, October 5, 2017).

Photo by D. Wicks

My good friend, Don Wicks, regularly sends me pictures of the Sandhill cranes that walk through his yard down in Florida!  They are members of a small, non-migratory population of cranes (the Florida subspecies) that are very well adapted to the proximity of humans. Photos of these birds walking confidently through urban and suburban neighborhoods interacting with their human neighbors are a bit startling. The cranes look more like intelligent aliens quietly exploring human habitations than wild animals out foraging for food.

Colorado serves as both a migratory staging area and also a very limited breeding site for Sandhill cranes, and the story of these birds in Colorado is a microcosm of the species’ history in the post-European settlement years throughout North America. Sandhill cranes along with many wild species of birds and mammals were intensively hunted as food by early, European settlers and miners. Further, the wetlands upon which the cranes rely for both food, refuge and nesting sites were being rapidly degraded or destroyed by human activity. Sandhill crane populations, then, greatly declined. In 1961 only 61 birds were seen at the traditional migratory stop-over sites in the state. These sites in the southern and northwestern parts of the state had historically been gathering sites for many tens of thousands of cranes! Further, by the early 1970’s there were only 25 breeding pairs of Sandhill cranes in Colorado!

Photo by Mwanner. Wikimedia Commons

Placement of the Sandhill crane on the Colorado Endangered Species List in the early 1970’s provided protection against hunting and further habitat destruction. Further, the construction of numerous artificial lakes and wetlands along with designation of established wetland areas as refuges also re-generated much needed habitat for the cranes. These events marked the beginning of a period of rapid recovery for these birds in Colorado. In 1993, Sandhill cranes were down-listed from “endangered” to “state-threatened,” and in 1998 to a “species of special concern.” Today, as we previously mentioned, tens of thousands of Sandhill cranes utilize Colorado wetlands on their spring and fall migrations. There are also 250 to 300 breeding pair of Sandhills nesting in the state’s protected breeding refuges.

Throughout North America the Sandhills have had such a robust recovery of numbers that all but one of states in their western migratory flyway have established hunting seasons  for the birds. Only Nebraska, the home of the Sand Hills for which the cranes are named, offers the cranes total protection from legal, human predation.

Whooping crane. Photo by Sasata, Wikimedia Commons

.I have been trying to figure out exactly why the whooping crane was pushed to the very brink of extinction while the Sandhill crane which faced similar stresses and pressures, is flourishing. In 1942, due to intense human hunting (for food and for feathers) and massive losses of wetland habitats, there were only 16 whooping cranes left on Earth. Today, even after years of intensive conservation efforts, there are still only 800 whooping cranes in the wild! The Sandhill crane, though, now has a population of over 500,000 individuals and is, as we reported in evaluating the Great Backyard Bird Count  two years ago,  expanding its summer, breeding range into upstate New York and the northern, Great Lakes- Midwest.

The Sandhill crane has always been more abundant than the Whooping crane. It is speculated that before the European settlement there were “only” 10,000 whooping cranes in North America. But, why were they, and why are they so uncommon?

Both of these birds prefer to live in or near wetland habitats. The Sandhill was originally found all across the United States but was almost completely extirpated from areas east of the Mississippi River by the 1930’s. Two of its eastern subspecies (the Cuban and the Mississippi Sandhill cranes) have very small, non-migratory populations and are under intense extinction pressures. The Florida subspecies, mentioned above, is also non-migratory but seems to be flourishing in the cities and towns of that state.  The two more dominant, migratory subspecies (the Greater and the Lesser Sandhill cranes) are also doing very well. The smaller, “Lesser” subspecies numbers over 400,000 individuals and the larger, “greater’ subspecies, has a population of 100,000 individuals.

Whooping cranes were once found throughout the middle of North America. Their current range, though, has shrunk down to a breeding site in the Northwest Territories of Canada and another “human-constructed” breeding  site in Wisconsin. They overwinter in a limited number sites on the Gulf Coast of Texas including the Aransas National Wildlife Refuge.

Both the whooping crane and the Sandhill crane are quite omnivorous and actively forage for similar types of foods (seeds and tubers, berries, insects, snails, amphibians, reptiles, small mammals and even nestling birds). Spilled grains (corn, wheat, sorghum etc.) in agricultural fields are especially important food sources for migrating flocks of either species. Whooping cranes tend to eat more animal materials than other cranes, and they lack gizzard stones which reduces the efficiency of their grain digestion.

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

Both species build their nests on the ground. Paired birds build up mounds of grasses and sedges that can be three or four feet in diameter and, after active stomping and compression by the birds, six or more inches tall.  A small, central concavity on the top of the mound is then layered with finer, softer materials to hold and cushion the eggs. Nest sites can either be on wet or dry ground. Both species typically produce two eggs in a clutch although the Sandhill is capable of having clutches of three eggs. Typically only one of the whooping crane eggs results in a chick. The Sandhill cranes, though, may hatch out both eggs.

Ground nesting may seem quite perilous for any species of bird. Numerous mammalian and avian predators would relish eggs, nestlings or even adult birds. Foxes, racoons, coyotes, cougars, lynx, bobcats, eagles, ravens, crows, great horned owls and gulls are prominent predators of cranes and crane nests.  Bobcats, in particular, because of their rising numbers in biotic communities from which large predators have been removed, and also because of their very stealthy hunting habits, kill a large number of crane nestlings. Alligators also take significant numbers of fledglings and adults of both types of cranes.

Adult cranes, both Sandhill and whooping, though, are not defenseless against predators. They have extremely powerful, strong-boned legs with three sharp, forward-facing toe claws (the fourth toe (the backward facing hallux) is extremely reduced). During non-breeding months most cranes will simply run away from an approaching predator, but if there are eggs or young in the nests the adult crane will charge at encroaching predators, flapping its broad wings and hissing loudly. It may also then use its claws and even its sharp, powerful beak to lash at, peck at and, possibly, even kill the threatening predator.

Sandhill cranes overwinter broadly across southern North America. Wetlands in southern New Mexico and Arizona are favored by the western populations, while the eastern populations overwinter in Florida and across the Gulf states. Whooping cranes, though, overwinter almost exclusively on the Texas Gulf Coast (with a very small overwintering cohort in Florida).

Photo by P. Kates. Flickr

So why do we have such an abundance of Sandhill cranes and so few whooping cranes? Maybe the Sandhills can eat more types of food and digest it more efficiently because of their gizzard stones. That especially has to help out migrating flocks feasting on spilled grain in fields in this time of the Anthropocene. Maybe the Sandhills can reproduce more rapidly. Two chicks in a clutch generates a much more rapid rate of population growth than just one! Maybe the Sandhills as reflected in their broad North American distribution can live in a wider range of types of wetlands than whooping cranes. Maybe this broader distribution has made the Sandhills less vulnerable to cataclysmic weather events like hurricanes and other storms. The Texas Gulf Coast, the whooping crane’s primary winter refuge,  is quite susceptible to major storm events!  Maybe the Sandhills, as reflected by their ability to live closely with all of those humans in Florida, are just more adaptable to new conditions and change in general than the whooping cranes.

There are lots of possibilities!

Flocks of cranes, by the way, are called “constructions” or “dances” (or “sedges,” or “sieges,” or “swoops”).  I can’t wait to go see our local, migrating dance of Sandhill cranes!