Sunday, October 30, 2011

Sandhill Crane

On Friday, Erika and I finally made the drive to Sherburne National Wildlife Refuge, about 90 miles from Northfield and just beyond the northwest suburbs of greater Minneapolis. Comprising over 30,000 acres of wetlands, oak savannas, and prairies, the refuge lies in the transition zones between eastern woodlands and prairie as well as northern and more southern forests. This wilderness, relatively close to the city, amazed us. The lakes and marshes almost reminded me of parts of Florida! One reason to visit Sherburne in October is the refuge serves as a staging area for migrating Sandhill Cranes. On Friday, refuge personnel counted 5352 Sandhill Cranes, and we had no trouble finding them in harvested fields northeast of the refuge. I was surprised how close they allowed us to approach (although we did not leave our car, which we used as a mobile bird blind).
Sandhill Cranes are awesome. Genetic studies suggest that these cranes are an old species without close relatives. They are more closely related to Australian cranes than they are to the Common Crane of Europe. Sandhill Cranes live to over 20 years, do not breed until they are 2-7 years old, remain in stable pairs over at least several years, and provide extended care to their young, staying together for almost a year. They usually only fledge one young per year.
Sandhill Cranes migrate and winter in large flocks. The use of migratory staging areas makes them particularly vulnerable to loss of wetlands. In Sherburne, the cranes roost in marshlands and feed in the surrounding fields during the day. As they fed, we saw several cranes dance. In the fall, these dances are antagonistic displays, protecting feeding space or family groups. As you might predict, antagonistic displays are most often done by males.
Family groups remain together from hatching through the following March. The advantages of family groups for the young include more feeding time, fewer aggressive encounters, and less time spent watching for predators. Juveniles outside of family groups tend to be in poor physiological condition.
Minnesota Sandhill Cranes migrate through the eastern and central United States and winter in Georgia, central Florida, the Gulf Coast and Texas. These cranes, along with others from Canadian breeding grounds, stop at staging areas during migration. Huge crane concentrations form in the spring for up to six weeks in the North Platte and Platte river valleys in Nebraska.
Cranes begin their migratory flights in the morning and usually stop near sunset. They cover about 250 km per day at speeds up to 83 km/hour (depending on wind conditions). They fly at altitudes of up to 2500 m. They prefer sunny days with tail winds. They are often inspired to migrate by seeing crane flocks overhead.
My source for almost all of this crane information is Tacha et al. (1992, The Birds of North America Online).

3 comments:

  1. Thank you, Dan, for the photos and the informative commentary. We went to Sherburne a couple weeks ago, but didn't know where to find the cranes, so we never did see them! :-( Good to see your photos.

    Betsy Kerr

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  2. When visiting a National Wildlife Refuge, it is always worthwhile to stop at the headquarters and ask about "good" birds....

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