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Wednesday, September 24, 2014

Predicting the Birds of Winter

Occurrence of Common Redpoll in Vermont
from 2002-12 based on Christmas Bird Count data.
Predicting the future isn’t easy. Crystal balls are unreliable and tarot cards can seem uselessly ambiguous. Weather forecasts do pretty well, but even with multimillion dollar radar equipment, they have their margin of error. Look at a graph of occurrence for Common Redpoll, and it can seem as random as flipping a coin. So how can one person accurately predict which northern-breeding birds will travel south, months in advance? Ron Pittaway has figured out.

Ron Pittaway is a prominent ornithologist in Ontario who began producing his famous ‘winter finch forecast’ over a decade ago. His forecast addresses ‘irruptive’ species of birds. These species are cold-hardy, and if they had it their way, would stay in the far north all winter long. But, in some years when food is scarce, they are forced to move south. Ron Pittaway predicts the movements of these birds by collating data on the seed crops of trees in the far north each year.

A Common Redpoll feeds in a birch
For example, Ron predicts a decent number Common Redpolls to move south this winter, because, “birch seed crops are variably poor to average in the boreal forest.” Redpolls like birch seeds, and without birch seeds in the boreal forest, the redpolls will move south. His forecasts not only predict which birds will come south with pretty good accuracy, they also give a glimpse into the life histories of these birds and how/where to observe them.

I, like many birders, eagerly await the winter finch forecast each year. As thousands of breeding songbirds disappear from Vermont each fall, it gives me something to look forward to in the winter to come.




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