Wednesday, November 12, 2014

"One Hundred Miles of Hawks"

Sub-adult Swainson's flying over Panama. Smithsonian Tropical Research Institute, Panama
The Swainson's hawks were late leaving the northern Plains this fall but a few weeks ago the last ones departed, eventually to be replaced by small numbers of rough-legged hawks arriving from the arctic.

The Swainson's is I think my favourite buteo, perhaps because it is still common enough that most days out in open country I can find one circling in the sky. But I am particularly in awe of its long migration, one of the lengthiest of any hawk. Each year the Swainson's hawks that nest here on the mixed-grass and moist mixed grass prairie travel 11,000 kms twice as they migrate between northern nesting grounds and the Pampas of Argentina.

What route do they take to get from northern to southern pastures? The people of Panama can tell you. In early November the narrowest parts of the isthmus of Central America witnesses one of the world's greatest avian spectacles. In the skies above Panama City, when clear migrating weather returns after several poor days, a river of hawks will pass by. Turkey Vultures, Broad-winged and Swainson's hawks numbering in the hundreds of thousands boil overhead in great kettles swirling their way southward.

On November 2nd this year, Panama City set a new record for counting hawks: two million hawks in a single day, which more than doubled the highest  previous count at Panama. From a press release put out by the Smithsonian:

"The official count from Sunday's massive raptor migration is 2,105,060 birds, most of them turkey vultures and Swainson's hawks," said George Angehr, a Smithsonian ornithologist.

And here is a news report from Panama

What caused the high count this year though? No doubt weather played a role, but the previous high of 900,000 was from 2013. Are the overall numbers of these species increasing? Certainly turkey vultures are increasing. And I have heard birders, naturalists and ranchers say that they are seeing more Swainson's hawks than they were a decade ago.

That could be good news and makes sense considering that their numbers were down to a record low after the mass die-off in the mid-90s caused by Argentinian farmers using Monochrotrophos and Dimethoate to kill grasshoppers. Six thousand Swainson's were killed directly by the poisons; many more were severely weakened. Monochrotrophos has been banned for almost twenty years, but Dimethoate is still in use in South America. However, it does seem that Swainson's hawks may have regained some of their numbers, at least here in Saskatchewan.

Birdlife International estimates that the total population of Swainson's hawks is around 580,000 and Canada may have a little more than 100,000 of those coming to spend each summer. Having departed from prairie farms and rangelands mere weeks ago to ride the river of hawks across the bottleneck of Panama, the northernmost Swainson's hawks on the planet are now gliding and soaring their way to the grasslands of Argentina where they will pass the winter eating crickets, grasshoppers, mice and voles.

Those of us who admire these elegant-winged hawks and want to keep seeing them in our summer skies need to do what we can to protect the wellbeing of their habitat at both ends of their yearly journeys. If the winter brings them plenty of prey free of pesticides, most of them will come back again in fine shape next April.
Swainson's Hawk, just north of Grasslands National Park

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