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Blowin’ in the wind

February 22, 2011

Doing most of my birding by bicycle has made me a little fitter than I used to be, given me a new appreciation of my local patch, and, above all, has made me more attuned to the weather.  A glance at my previous post will give you an example of what happens when you blithely ignore a forecast for nasty weather.  In particular, I’m paying close attention to the wind these days.

In the Okanagan Valley, we only get two kinds of wind— south and north.  The south wind is the prevailing wind, blowing for days sometimes as the Pacific coast, just over the mountains to the west, is being battered by winter storms.  The north wind is less common; in the winter it occurs as Arctic air flows like a huge river through passes in the Rockies and fills the southern valleys of British Columbia.

Yesterday, two things got me out of the office for an extended lunch break.  One was a call from my son Russell, telling me that the Snow Goose that has wintered in Summerland, the goose that I’ve looked for twice already, was sitting on the beach at Sunoka Park.  The other thing was that for the first time in days it was perfectly calm.  I biked up to the north end of the West Bench, made a mental note of the Western Bluebirds in the Russian olives, then barrelled down the Sage Mesa hill to the highway along Okanagan Lake.  The calm water made for good viewing conditions—little groups of Horned Grebes far offshore, a male goldeneye diving off a distant point.  When I could see Sunoka Park in the distance I immediately noticed a white spot!  Stopping, I checked the shore with binoculars—there were actually four or five white spots, all buoys marking the swimming area.  No white geese in sight.

I began the usual tour of Trout Creek’s maze of roads, peering into each orchard and vineyard for wayward goose flocks.  Finally, as I gave up and started back south, I saw a small flock of Canadas beside the road ahead.  I stopped and looked for more in the orchard and there, only 20 metres from me, was a gorgeous adult Snow Goose.  I had a celebratory sandwich and coffee, then began the 10-kilometre return trip.  To my dismay, a strong south wind suddenly sprang up, filling the lake with whitecaps and cutting my cruising speed from 30 kph to 11 kph.

As I slowly pedalled on, fighting the wind, my thoughts turned to how birds deal with wind, especially during migration.  One of my favourite bird stories is the migration strategy used by Blackpoll Warblers (I tell this story in more detail in my book An Enchantment of Birds).  These birds spend the winter in northern South America, then migrate north in spring through the eastern United States and spread out across the boreal forests of northern Canada and Alaska.  In late summer they migrate south, but use a rather different route.  Instead of moving directly south (though the species is a common breeder in the northern half of British Columbia, we never see them in southern British Columbia), they fly east to the Atlantic seaboard, from Newfoundland south to about Delaware.  There they feed, fatten up (doubling their weight to 21 grams) and wait for the wind.

An immature Blackpoll Warbler mistnetted in the southwestern Yukon, near the beginning of its epic journey across Canada, then the open Atlantic, to reach wintering grounds in South America

When the right weather system arrives, bringing strong winds from the northwest, they take off over the Atlantic, continuing until they encounter trade winds that blow them southwest to the Antilles and northern South America.  The entire 3500-km over-ocean trip takes about 88 hours of nonstop flying, all powered by the wind.  If the wind fails en route, the birds descend and look for any dry spot to rest, the lucky ones finding ships or even islands such as Bermuda.

You can see the different seasonal patterns of Blackpoll Warbler sightings on eBird:  spring and fall (look at the southeastern states to see the difference).

While most North American songbirds don’t make the adventurous flight that the Blackpoll Warbler does, many do fly across the Gulf of Mexico twice a year—no mean feat in itself.  And several shorebirds, notably the Bar-tailed Godwit and Pacific Golden-Plover, fly non-stop over the Pacific on their migrations.  The vulnerability of these birds to the vagaries of wind direction and strength can have deadly consequences.  Rob Butler analyzedBreeding Bird Survey data for a number of songbird species in North America and found that spring populations tended to be low after autumns that were unusually stormy in the Gulf of Mexico.  Climate change models predict that we will experience more frequent and stronger weather events, so unpredictable winds may be yet another difficulty songbird populations will have to face in the coming decades.  My tough ride home yesterday seems paltry in comparison.

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