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Swainson’s hawks start to gather in preparation to migrate

Bill Schiess,
Big mouths often cause trouble for the owner of that mouth.
A young Swainson’s hawk left its perch on a fence post and harvested a vole in the newly swathed alfalfa field near Mud Lake. As it flew back to the post, it started bragging about its catch only to be attacked by two adult Swainson’s who stole the youngster’s brunch.
In the same field, an irrigation pivot held 38 hawks, mostly Swainson’s, but some Red-tailed and a Prairie falcon joined them, waiting to harvest some food. The Swainson’s are the summer hawks of southeastern Idaho and are very social as they are starting to gather in large scattered flocks called “kettles.” There are several kettles located from Idaho Falls to Mud Lake where these hawks are gathering before migrating to South America for the winter.

Bill Schiess,
They do not gather in pairs or in a flock formation as waterfowl do, but will be in a loose group from the ground to several hundred feet in the air. Often at night, they will roost together in large trees with over 100 in a single large cottonwood.
The Swainson’s hawks are also called Grasshopper hawks and will spend most of their day feeding on grasshoppers, dragonflies and an occasional rodent to trick the taste-buds. Newly swathed and baled hay fields and harvested grain fields are great places for them to find plenty of food.
Each day a kettle of Swainson’s will fly in a vortex as they practice their flying techniques in preparation for their 1200-mile flight south. When they get serious about migration, they will fly high in the air, catch a thermal and soar with it until they need a rest. Thousands of Swainson’s form large kettles as the migrate through Mexico and Central America.

Bill Schiess,
During the 1990s their wintering grounds in South America became very dangerous for these medium-large raptors because of the use of pesticides used to kill grasshoppers. In one season an estimated 35,000 died in Argentina alone where they fed on grasshoppers poisoned with monocrotophos. Argentina along with several other countries have now stopped the use of these dangerous pesticides and the Swainson’s have now made a comeback and we are the recipients of their increased numbers.
Several times this week while coming back from watching elk, deer and pronghorns, I watched these magnificent birds. There are many color variations among the Swainson’s as there are “light’ and “dark” morphs; and right now there are both immature and mature birds which help confuse identification with the mixed flocks of them. The dark morphs seem to dominate the population of those in southeastern Idaho this fall.

Bill Schiess,
Swainson’s hawks are the most numerous hawks during the summer in our area, but by the first of October most of them will be grasshoppering in South America. By the end of November, they will be replaced by rodent killing machines, the Rough-legged hawks that have been nesting in northern Canada and Alaska. They will also be joined by the Red-tailed hawks that have been nesting in Island Park and the mountains around the Upper Snake River Valley.
With a predicted drop in temperature coming next week these birds may be abundant one day but gone the next. If you get a chance to watch a kettle of Swainson’s, enjoy it; they can be very entertaining while they steal each other’s food or chase their favorite insects around. Please enjoy the great outdoors safely, and let me know if something out there piques your interest.

Bill Schiess,
The post Swainson’s hawks start to gather in preparation to migrate appeared first on East Idaho News.

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