Friday, January 28, 2011

Sandhill Cranes: An Ancient Lineage

Greater Sandhill Cranes in early light
(Photos by Narca)

Sandhill Cranes are a huge draw at Bosque del Apache National Wildlife Refuge in New Mexico, and the inspiration for their annual Festival of the Cranes, now in its 24th year. When you rise early, before dawn breaks, and venture out to the gatherings of cranes, where they sleep during the long winter night along the margins of wetlands, you may hear their primeval, haunting rattle, long before the light reveals the masses of the great birds.

Joy in the Morning (Mixed media by Narca)

And primeval they are: a 9-to-10-million-year-old crane skeleton found in Nebraska is identical to that of the modern Sandhill Crane's, making it the oldest known bird species still surviving! Biologists argue about how many subspecies of Sandhill Cranes there are, either five or six. Three of those are non-migratory, living year-round in their strongholds in Cuba, Mississippi and Florida. The others (Greaters, Lessers and––some say––Canadians) migrate each year between northern breeding grounds and more southerly wintering grounds, such as Bosque del Apache. Here at Bosque, the Greater Sandhills predominate, with a sprinkling of Lessers mixed in.

Lesser Sandhill Cranes have shorter legs and bills.

Why are Lesser Sandhill Cranes smaller? They are actually a great illustration of "Allen's rule," which states that warm-blooded animals from colder climates usually have shorter limbs than their equivalents in warmer climates. And indeed, Lessers nest in the High Arctic, at the highest latitudes of any of the Sandhill Crane subspecies, and their bills and legs are noticeably shorter than those of other Sandhills.

As the early sun slants across the bosques (or woodlands) of the Rio Grande, we notice an odd pairing of cranes. A young Lesser Sandhill (about 3 feet tall) is staying right next to an adult Greater Sandhill (over 4 feet tall). Their motions mirror each other's, first as they walk, and then in preflight posture with their necks craned. When they finally fly, they fly together, just the two of them.

A Greater and a Lesser Sandhill Crane keeping company

Rod Drewien, our friend and crane specialist, suspects that this young Lesser was a member of a family group that was disrupted by hunting in a state to the north of New Mexico. The immature bird became lost, and winged its way to Bosque del Apache, where it appears to have found a kindred spirit in this adult Greater.

So in the case of our Odd Couple, I'm wondering whether a pair bond is actually forming, and if it is, where would this odd couple nest? In the High Arctic with the other Lessers? Or perhaps with other Greaters somewhere like Gray's Lake in eastern Idaho? Talk about a basically dysfunctional marriage!

Sandhill Crane Pas de Deux

Rod tells me that some day I have to visit the Lesser Sandhill Cranes' primary staging area along the Platte River in Nebraska, where 80% of the world population of Sandhill Cranes (as many as 800,000) amasses in March along a 75-mile stretch of river, in an immense roil of wings and dancing. Here they gather, eager to push north to their nesting grounds, but compelled to wait until winter releases its grip on their breeding territories. Okay... a month and a half from now... I'm ready!

If you are ready, too, a good place to go is Audubon's Rowe Sanctuary near Kearney, Nebraska. Or, if you enjoy exploring with a guide and like-minded companions, both Naturalist Journeys and WINGS offer an annual jaunt to the Platte River to witness the staging of the cranes.

Sandhill Cranes cover about 300 miles in a day of flying!

No comments:

Post a Comment