I was on the horn, reaching out to one of my closest homeys, calling to invite him to come help me comb some hilly, brushy country up by Colville next week. For several years, I’ve been trying to catch up with one of the big whitetailed bucks that favors a secluded hollow along the top of a too-steep ridge. I figured that he could help. Not so, he figured, since he was in Arizona.
“What…? What’s in Arizona?” I asked. He laughed and said, “Arizona…”
Suddenly it dawned on me; this is migration time – for both our feathered and snowbird friends. I have long marveled at the mysterious forces that trigger migration for any of the critters scattered across the face of the globe. I asked Homey “What made you decide to go now?” He paused for a moment and said, “Mama said it was time to go.”
That snowbird migration mystery solved, I was now free to think about birds.
For a couple weeks now, we’ve all been watching the big mixed-species flocks of various birds undulating across the valley. The authors of “The Birder’s Handbook” (Ehrlich, Dobkin and Wheye) think these mixed flocks may have to do with increased feeding efficiency – more birds able to find more food. Some argue that it has more to do with mixing far-sighted birds with near-sighted birds for safety. Whatever brings them together, at one time or another you will see mixed flocks of starlings, red-winged blackbirds, horned larks, wrens, sparrows, nuthatches, pipits and others. In all likelihood, some of the species in the flock are readying for winter in Paradise, while others are preparing to head south. I’ve long considered the possibility that they are all just saying their good-byes.
Be that as it may, we still wonder about what triggers migration. How do they know when? And furthermore, along these great traveling distances between breeding and wintering grounds, how do they know where or how?
As far as knowing when to head south, most votes go to photoperiodism – the changing length of day and/or the amount of sunlight reaching some critical level.
To me, the most interesting part of the equation is the part where they birds find their way back and forth. It is in this area that experiments and careful observations have shed most light in the last decade or so. Clearly, we have vastly underestimated our feathered friends through history.
Birds apparently acquire their navigation information from five primary sources: (1) the stars; (2) the sun; (3) topographic features of the land over which they fly (including wind direction where it is influenced by land forms); (4) earth’s magnetic field; and (5) scent. Given today’s tools of science, ornithologists are breaking new ground and filling in missing pieces in all five of these sources. The clues are used in some hierarchical way, and in different orders by different species.
Captive indigo bunting youngsters learned a false night sky pattern as they grew. Once released to migrate, they reacted and oriented to a misplaced star pattern. Oscar Gordo’s work in climate research has tied migration timing and pattern changes to weather and climate shifts, with temperature emerging as the dominant factor.
With the ability to look at global energy patterns, Deppe, Wessels and Smith produced a very interesting space based study. The study was published in the Alaska Park Science Journal in 2006. Looking at bird migration on a global scale and comparing it to energy and food availability patterns, they developed a conceptual framework for examining individual energy budget and survival issues within migration paths worldwide.
In the May 13, 2010, issue of Nature, Ritz, Thalau, Phillips and the Wiltschkos reported on their discovery about birds’ eyes. It appears that a special light-absorbing molecule in the eyes of migrating species allows them to actually visualize the earth’s magnetic field, perceiving the magnetic field lines as a sort of road map. One researcher has suggested that birds may see those magnetic lines as patterns of color, or light, superimposed over surroundings as they fly.
The whole business is fascinating, of course, and there is vastly more to learn – at any level you like. Check out migration patterns and timetables at www.birdnature.com/migration.html. Find out all you ever wanted to know about bird tracking, specific North American pathways (and books on the subject) on the terrific web page at www.backyardnature.net.birdmgrt.htm. You will find very cool family games and interactive pieces at the Smithsonian’s Migratory Bird Center, with its cool games and interactive pieces, at nationalzoo.si.edu/scbi/migratorybirds/education/kids_stuff/woth_game/default.cfm.
No doubt, somewhere online, you will find information about “Snowbird” migrations, too. Maybe you can find out why on earth they would leave Paradise.
