Cranes are among the oldest living birds on the
planet. Fossil records place cranes in Nebraska more than nine million years
ago, long before there was a Platte River, which by comparison, is a
youthful 10,000 years of age. Sandhill cranes have
adapted well to the change in landscapes over time and their populations are healthy and continue to rise.
Sandhill Cranes and the Platte River
Sandhill cranes have been found as far north as
Alaska and Eastern Siberia. In order to reach these destinations, cranes
must build up enough energy to complete their long journey and to begin
breeding. For the cranes, the
Platte River Valley is the most important stopover on this migration. The
river provides the perfect spot to rest, and the nearby farmlands
and wet meadows offer an abundance of food. Without the energy gained at
the Platte, cranes might arrive at their breeding grounds in a weakened
condition -- where food may be limited until the spring growing season
begins.
The Platte River region has a variety of
habitats that support cranes. The most important is the Platte River
itself. The river is very shallow and sandbars dot the channels. It is
here the cranes rest at night, gaining protection from
predators like coyotes.
In the morning, cranes shuffle up and down the river waiting for the
sun to pop up over the horizon. As the sun rises,
cranes head out to feed and loaf in the surrounding fields. During
the day, cranes "dance" to relieve the stress of migration and strengthen
pair bonds. Cranes are very "social" birds and in the evening,
congregate in wet meadows before heading back to
the river for the night.
Cranes are omnivorous, eating both plant and animal materials.
With the abundance of cropland in the Platte River valley, corn makes up
nearly 90 percent of their diet, providing carbohydrates for fat
production. Wet meadows along the river provide invertebrates that
make up the remainder of their diet. Worms and snails provide
protein, with the snail shell being a source of calcium that is essential
for egg development.
Migrate or not?
There are six subspecies of sandhill cranes, of which three are
migratory and three non-migratory. Two of the non-migratory subspecies
are endangered: the Mississippi and Cuban sandhill crane. All of the
migratory subspecies pass through Nebraska and their populations are
thriving (~600,000). The most numerous is the lesser sandhill crane, which
is the smallest subspecies. The Canadian sandhill crane comprises about
15 percent of the birds staging along the Platte, and the greater sandhill crane
about 5 percent.
The wings of a crane are approximately six feet
long. Cranes are lazy fliers, relying on thermals to carry them along. Thermals are rising columns of warm air, and when southerly winds
start to blow, you will see cranes testing them for flight conditions.
Sometimes during flight, the upward wingbeat is very quick,
giving cranes a mechanical look. Cranes ride thermals so efficiently that they
have been seen flying over Mt. Everest (~28,000 feet).
An adult sandhill crane is between three and
four feet tall and weighs 6 to 12 pounds depending on the subspecies. Adults have bright red skin patches
on their crowns and are usually gray with brown stains. Juveniles have
brown skin patches and can be dark grey to brown in color. Crane's can
also stain their feathers by preening after they have
been probing the ground for food.
Their bills and
feet are important tools. A crane's bill is very sharp and
sturdy, useful when probing frozen soil. The edges are
serrated to grasp slippery food like worms and snakes. Not only is it used
for preening, it is also used as a weapon.
The feet and legs work in conjunction with the beak. The foot has three
long toes with claws on the end. These claws are very sharp and can be
used for scratching in dirt to find food and for protection. When a crane
is threatened, it will use its wings to maintain its balance and then
jump up and strike at the attacker with its feet.
How do they do that?
Do you ever wonder how cranes
stay warm while standing for hours in near-freezing water? They can reduce the amount of blood that has to be warmed by constricting
blood vessels in their feet. Also, the arteries and vessels in their
legs
are
right next to each other so the colder blood is warmed before it reaches
the body.
Understanding cranes better will add to
your enjoyment and appreciation as you watch them in their daily
activities and marvel at the magic of their
migration.
