Sandhill cranes are a threat to Siberian breeding birds

 

 

USA 2000-01
Emitting an incredible crescendo of trumpeting, sandhill cranes (Grus canadensis) take flight from the Platte River, flock after flock heading for the surrounding maize fields to feed on waste kernels. (Photo copyright © by Kaj Halberg)

 

 

On a cold March morning, before dawn, a dozen warmly clad people are walking behind their guide down a path, which leads to a large blind on the shore of the Platte River, in central Nebraska, United States. From the river, we hear a huge chorus of trumpeting sandhill cranes (Grus canadensis), but the birds themselves can barely be seen, roosting on sand bars in the river, only about a hundred metres away.

As the rays of the rising sun penetrate the morning mist, the birds take shape, and a fantastic scene unrolls in front of us. In the shallow waters of the river, about 50,000 cranes are standing shoulder by shoulder. Their trumpeting now intensifies, and the birds begin to shift restlessly, a few of them performing their graceful dance. Then, with an incredible crescendo of trumpeting, the birds take flight, flock after flock heading for the surrounding maize fields, where they eat waste kernels, left over from the harvest. Farmers consider the cranes beneficial, as sprouted maize kernels from the previous year are regarded as a weed.

Every year, during their spring migration in March and April, huge flocks of sandhill cranes roost here for a few weeks before continuing to their breeding grounds in swamps and lakes further north. The cranes used to roost in many prairie rivers, but today most of these rivers are regulated by dams, causing most of the sandbars, on which the birds roost, to be either submerged or covered in dense vegetation, such as willows, because the sandbars are no longer inundated by spring flooding. Along the Platte River, much work is done to clear these thickets, causing about 80% of the world population of sandhill cranes to roost here.

 

 

USA 2000-01
In March, huge flocks of sandhill cranes gather in the Platte River, Nebraska, roosting here for a few weeks before continuing their migration to the breeding grounds further north. (Photo copyright © by Kaj Halberg)

 

 

Successful species
The sandhill crane is the most numerous crane species in the world, numbering around 650,000. Today, five subspecies are recognized: canadensis, breeding in eastern Siberia, Alaska, and northern Canada, comprising four fifths of the whole population; tabida, breeding in southern Canada, and northern and western U.S.; pratensis, breeding in Florida and the southernmost part of Georgia; pulla, breeding in the southeastern corner of the State of Mississippi; and finally nesiotes, breeding on Cuba. A sixth subspecies, rowani, is no longer accepted, and some authorities only acknowledge two subspecies, canadensis and tabida. Northern populations – including the Siberian breeding birds – spend the winter in southwestern U.S. and Mexico, while southern populations are resident. Some populations, e.g. in Mississippi and on Cuba, are very small and threatened with extinction.

In Nebraska, researchers have found 10-million-year-old skeletal parts of a crane, very similar to the ones of the modern sandhill crane, but it is probably a different species. However, 2.5-million-year-old subfossils of sandhill cranes have been found, still making it one of the oldest living bird species today.

 

 

USA 2000-01
The world population of the sandhill crane is increasing, undoubtedly because they have easy access to waste maize kernels in agricultural areas. Farmers consider the cranes beneficial, as sprouted maize kernels from the previous year are regarded as a weed. (Photo copyright © by Kaj Halberg)

 

 

Chukotka 2011
Sandhill cranes in courtship display, Chukotka Peninsula, eastern Siberia. (Photo copyright © by Kaj Halberg)

 

 

Chukotka 2011 
Nest of sandhill crane, Chukotka Peninsula, eastern Siberia. Cranes usually lay two eggs, sometimes one or three. (Photo copyright © by Kaj Halberg)

 

 

Threat to Siberian breeding birds
The world population of the sandhill crane is still increasing, undoubtedly because they have easy access to spilled maize kernels in agricultural areas of the U.S. and Canada.

Recently, the sandhill crane has expanded its range far west into Siberia, and the Russian population today exceeds 10,000 birds. Traditionally, Russian hunters do not shoot the cranes, but in later years the sandhill crane has become so numerous that some hunting of the species takes place. As the cranes are omnivorous, they eat whatever they can find: roots, insects, mice, and eggs and young of numerous species of birds.

In later years, several Siberian wader species have declined drastically, mainly due to habitat destruction on their flyways between breeding and wintering grounds. In China, Korea, and Vietnam, huge areas of coastal shallow waters have been converted into shrimp farms, salt pans, or fields – areas which migrating waders are dependent on for fattening up, before continuing to their breeding grounds. Many waders, arriving in Arctic Siberia, are now in a poor condition, which means that they produce fewer young – or simply skip breeding. Thus, production of chicks has plummeted in many species, and one species, the spoon-billed sandpiper (Eurynorhynchus pygmeus), is critically endangered, with less than a hundred breeding pairs.

Under these circumstances, marauding sandhill cranes do make a difference, and the beautiful birds have become a threat to Siberian breeding waders.

 

 

Reference
Meine, C.D. & Archibald, G.W. (red.) (1996). The cranes: Status survey and conservation action plan. IUCN, Gland & Cambridge

 

 

(Uploaded February 2016)

 

(Revised April 2017)