Hundreds of Swainson’s hawks dotted the air space over Osgood Monday morning

Photos: Bill Schiess |

Our summer hawks, the Swainson’s, are getting ready to head to Central and South America for the winter. I received an email this week from a woman that told me there were hundreds of hawks over Bear Island, 10 miles north of Idaho Falls, about 4 p.m. on Sunday, Sept 6.

Early Monday morning as the sun was fighting its way through its smoke-blanket, I drove from Roberts to the Osgood interchange just east of the freeway, counting 247 Swainson’s hawks. They filled trees, covered irrigation pivots and worked the recently harvested fields as they all were looking for their favorite foods: grasshoppers and dragonflies.

Some hawks would run their prey down, while other birds would pick off flying insects with their small feet and eat them without landing.

Also known as the Grasshopper hawk, Swainson’s are very social and congregate in large scattered flocks called “kettles” to feed or to get ready to migrate.

“They were flying in a vortex from very near the ground to several hundreds of feet high,” the lady commented in her email. “No pairs, not a flock formation, just sailing roughly in a vortex.”

She had probably witnessed a kettle practicing their flying technics in preparation for their 1200-mile flight south. When they get serious to migrate, they will fly high in the air, catch a thermal and soar with it until they need a rest. Thousands of Swainson’s have been observed migrating through Mexico and Costa Rica.

During the 1990s, the wintering grounds in South America became very dangerous for these medium-large raptors because 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, has now stopped using these dangerous pesticides and the Swainson’s have made a comeback.

As I watched these magnificent birds Monday, it appeared that there were several species of hawks involved in getting their breakfast. There were some that were light-colored and some that were almost black. Swainson’s hawks have a “light” and a “dark” morph. Right now, there are both immature and mature birds that confuse the identification of them.

East of the Rocky Mountains are mostly light morph birds, while about 10 percent of birds in the west are the dark morphs. The birds north of Idaho Falls had a high percentage of darkies in that kettle.

Swainson’s hawks are the most numerous hawks during the summer in southern Idaho, and by the first of October, most will be hunting grasshoppers 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.

I would like to thank the woman who emailed with an observation of the Swainson’s hawks. It gave me an excuse to go searching for what is happening in the wildlife world.

By the way, Swainson’s hawks feed on small rodents and other creepy-crawly things during their nesting time and before the grasshoppers become abundant.

Please enjoy the great outdoors safely, and let me know if something out there interests you.