Sunday, January 6, 2008

Flights of sandhill cranes inspire questions for an expert wildlife biologist

Simply Living

(First appeared in Orlando Sentinel January 6, 2008)

There is a mystery surrounding sandhill cranes that has intrigued me for years. It concerns their evening pattern of flying in great V's toward some unknown location. If you've been outside about 5:30 p.m. and happened to look upward, you might have seen them too. Maybe, like me, you've also wondered, "Where are they going? And why are they going there?"

My curiosity has peaked in recent weeks as I began noticing their distinctive flight patterns just before sunset. Looking up, I see the sky dotted with cranes flying overhead in flocks of 14, 16, two dozen or more at a time.

They take to the sky with uncanny regularity, as if an internal buzzer has signaled them to stop feeding and go aloft before dusk. Coming from all directions, these majestic fliers with the gray feathers and red crowns flap their wings in unison and point northeast.

Their evening flight takes them directly over our property, causing me to stop whatever I'm doing to ponder their patterns. Is there some great roosting spot where hundreds of cranes gather at night for communal repose? If so, where is it?

To find answers, I contacted Florida's pre-eminent crane researcher Steven Nesbitt at his home in Gainesville. According to Nesbitt, a communal resting place is exactly where they're going.

"Cranes are social birds," explained the retired wildlife biologist formerly with the Florida Fish and Wildlife Conservation Commission. "Sometimes hundreds or, in some places, even thousands, will roost together in one spot."

They gather for protection as much as socialization. With predators in Florida such as alligators, bobcats and coyotes, sandhill cranes seek safe roosting spots free from surprise attacks.

"Typically, they want open marsh or shallow open water," said Nesbitt. "Since cranes cannot perch, they are obligated to spend their time on the ground or standing up in water that's two to three inches deep. They look for a lake bottom that is solid or firm, not one that's mucky or with a whole lot of vegetation. They also roost on islands in lakes and shallow water."

Nesbitt postulates that the many of the cranes I've noticed are "northern migratory cranes that have come to Florida for the winter from the Great Lakes, eastern Minnesota, Wisconsin and southwest Ontario."

There are six subspecies of sandhill cranes worldwide with a total population of about 400,000. Florida's year-round residents are called Florida sandhill cranes (Grus canadensis pratensis) while the migratory birds that winter in Central Florida are greater sandhill cranes (Grus candensis tabida).

Migratory cranes start arriving in Florida in late October and peak between Thanksgiving and Christmas. They remain in the Sunshine State through mid-February before leaving for the long flight back North.

Despite belonging to different subspecies, the native and visiting birds intermingle freely, occasionally feeding, flying and roosting together. That explains why large V's of birds appear in wintertime when the area's total crane population swells.

"The last time it was recorded," Nesbitt said, "the Florida sandhill crane population was in the 4,000-to-6,000 range. The population of greater sandhill cranes is approximately 40,000, and most of them migrate to Florida in the winter."

Sandhill cranes usually roost within about a mile of their feeding range area of 500 to 1,200 acres.

"They're as much an upland bird as a wetland bird," he said. "They do a lot of their feeding in pastures and grassy uplands."

Maybe that's why I seldom see more than an occasional pair here on our property -- with an ever-expanding number of bamboos, pine and oak trees, our land no longer contains large enough open pastureland to satisfy a large flock's needs.

Of the many wondrous birds in Florida, sandhill cranes are among my favorites. Their great size is part of what makes them special. About 4 feet tall with a wingspan of almost 7 feet, these beautiful birds are just slightly smaller than North America's largest bird, their endangered cousin the whooping crane.

Their mating habits are also endearing. Like geese and swans, cranes are monogamous. Not only do they choose lifelong partners -- and live an average of 25 years -- but both sexes also share in parenting chores, with the male birds helping to incubate the eggs and raise the babies.

With a tendency to return to the same habitat annually and an easy comfort with their human counterparts, sandhill cranes become familiar sights in many a Central Florida neighborhood.

Finally, it's their distinctive call that draws me to them with wonder and admiration. A sandhill crane's croaky vocalization is like a beacon back to prehistoric days. Fossilized remains of birds with bodies almost identical to modern sandhill cranes are estimated to be at least 10 million years old.

Although Nesbitt helped clarify much of the sandhill crane mystique, I'm still curious about those expansive marshy areas where hundreds of cranes roost at night. Someday, I'd like to see one in person. If any readers know of such a spot and are willing to show it to a passionate observer, I'm up for the task. Anything I find out will be shared in a future column.

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