July 19, 2018
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Bird migration is more complicated than you think

Bob Duchesne | BDN
Bob Duchesne | BDN
A common tern chick (left) lets its parent hear about its displeasure.
By Bob Duchesne, Special to the BDN

Birds fly south for the winter. Oh…if only it were that simple.

It’s easy to think that summer life is routine for our birds until they decide to leave, and they then fly directly south to their winter homes. Some do. Others meander. Arctic terns are the world’s champion migrants, partly because some fly all the way from the Arctic to the Antarctic, but also because they wander ridiculously. For instance, Arctic terns nest on some of Maine’s islands, and when our birds leave, they are as likely to fly over to Africa as they are to South America.

Last Sunday, the Isle au Haut Ferry made its last puffin trip of the season to Seal Island. I tagged along as official spotter, a role that I had also filled two weeks earlier. What a difference two weeks make! Puffins share the island with their larger cousins, the razorbills. Typically, razorbill chicks are ready to go to sea about two weeks earlier than puffin chicks. On my previous visit, there were plenty of razorbills milling about. Two weeks later, not a single bird could be found.

When razorbill young are fledged, it’s the father that leads them away from the island. They swim to wherever the food is. Dad feeds the chick for a while, but gradually the little tyke learns to catch its own meals.

Meanwhile, when puffin chicks go to sea, they’re completely on their own. One fateful night, the chick walks out of its burrow, stumbles to the water’s edge, and just swims away. It will not touch land again for 4-5 years, when it is mature enough to start its own family. Perhaps as an inducement to leave, the puffin parents eventually stop bringing food to the chick. Thus, on our last visit, all the adults were just milling around our boat, floating or flying, their parental obligations complete. There were hundreds more puffins to watch than usual.

The terns weren’t so carefree. Adults continue to feed young after they’ve fledged, and the young terns were chasing their parents relentlessly, begging for food. No longer confined to their nesting islands, young terns could follow their parents to sea in search of food, pestering them the whole way.

In bird world, everything goes a little nuts once the chicks leave the nest. For instance, when it’s time to go south, some young birds head north. Herons and egrets are notorious for this behavior. There are many great and snowy egrets that nest in southern Maine, almost none above Thomaston. But once breeding is complete, some disperse northward, moving into Bangor and a few coastal marshes.

Red-headed woodpeckers breed nowhere near Maine. But when families disperse, some wander north, and a few youngsters can reach Maine. Forster’s terns don’t breed here either, but a handful wander this way each autumn. Other species disperse northward. This may be Mother Nature’s trick to encourage some species to expand their ranges. Youngsters who have no obligation to parents or siblings may go north before going south, just to see if there are new places to colonize next spring.

The post-nesting, pre-migration period is chaotic, even in your own backyard. Many family groups are still together. A family of five blue jays has been coming through my yard lately. Although they have been doing so silently, I’m alerted to their presence by the whiny “zhree” of the red-eyed vireos, warning their own families to be careful around the jays.

Very shortly, warblers will give up all semblance of family bonds and join with other species to form foraging flocks. Large groups of different species work the trees together, looking for food and watching for hawks. As they move through the forest, they utter quiet chip notes to keep themselves organized.

Birds get clues that it’s time to migrate from shortening daylight, declines in temperature, and changes in food supply. As these signals intensify, birds get restless. Europeans noticed this seasonal restlessness in caged songbirds centuries ago. German behavioral scientists even studied the phenomenon by subjecting caged birds to these cues and observing their reactions. They called the restlessness zugunruhe. Such restlessness also occurs in other migratory animals, from whales to caribou.

Many of our songbirds are neotropical migrants, wintering in Central and South America, or enjoying tropical islands in the Caribbean. Longer migration requires earlier departure, and these birds are already starting to get restless. After a month of relative quiet, it’s getting noisy out there.

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.

 


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