A New Look at Altitudinal Migration

AUK-16-228

(Alice Boyle; 29 March 2017)

I became a birder in my early 20s when I moved to Costa Rica to play in the Orquesta Sinfónica Nacional.

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One of the things that puzzled me from the start were descriptions of the seasonal migrations of birds within that tiny, lovely, benign country. I grew up in a place where bird migration seemed not only logical, but frankly the ONLY sensible thing to do in winter. But why would some birds move up and down mountains each year in a place where the weather is always warm and food hangs from the trees wherever you go?

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few other researchers were asking similar questions in other parts of the world.

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Part might have to do with the perception that these are not “real” migrations.

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It turns out that we have LOTS of birds in North America that make similar types of movements. In fact, roughly the same proportion of the North American avifauna migrate up and down mountains as does the Costa Rican avifauna—20% to 30% depending on how you count it. With the exception of the Himalayas, reports from other avifaunas seem consistentwith this figure.

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The fact that such movements are often partial (not all birds migrate), facultative (not genetically hard-wired), and short-distance actually makes them more attractive subjects for many types of migration research. We have far better chances of determining what ecological conditions tip the cost-benefit balance toward migrating in species that have built-in control groups in the form of resident individuals.

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If we are to protect our avifauna for future generations, understanding these movements will be as important as understanding the marathon flights of the migration poster children.

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