Swainson’s Hawks

Swainson's Hawk, (Buteo swainsoni), Photo Courtesy US FWS
Swainson’s Hawk, (Buteo swainsoni)
Photo Courtesy US FWS
Swainson's Hawk, (Buteo swainsoni), Photo Courtesy US FWSSwainson’s Hawk, (Buteo swainsoni)
Photo Courtesy US FWS

The Wellsville Mountains of N. Utah are known for their steepness, spectacular beauty, and an extraordinary fall raptor migration. The perfect mix of thermal uplift on its west slopes funnels the birds along the east side of the Great Salt Lake to their southerly destinations. Many species- eagles, falcons, accipiter’s, and buteos grace its slopes. The migration occurs primarily from mid-August to mid-October. Last Saturday’s hawk watchers were treated to 300 plus birds consisting of 15 species.

There is one in particular that is known for its extraordinary abilities and unusual behaviors that I will dwell on, that being the Swainson’s hawk. Nearly the entire population of these amazing birds will navigate their way to Argentina, a distance not equaled by any other raptor.

This species was named after William Swainson, a British naturalist. It is also known as the grasshopper hawk or locust hawk, as it is very fond of locusts and grasshoppers and will voraciously eat these insects whenever they are available. They have the unusual behavior of congregating in large numbers in fields to attack their prey. I’ve counted over 100 birds occupying cut hay fields in a half mile distance.

Breeding Swainson’s hawks are opportunistic feeders that respond quickly to local concentrations of food and rely heavily upon small mammal, bird, and reptiles such as young ground squirrels, rabbits, pocket gophers, mice, small birds. Birds taken include Mallards, young Sage Grouse, American kestrel, and young short-eared owls. Reptiles include snakes such as racers, gophers, striped whipsnakes, and lizards. Amphibians include tiger salamanders and toads.

In Argentina, Swainson’s hawks feed on flocks of the migratory darner dragonfly, following the hordes of insects and feeding mostly on the wing. Local outbreaks of locusts may also be exploited. There is also some evidence that road-killed birds and animals are consumed both on the wintering grounds and on the breeding grounds. They commonly follow tractors during haying or ploughing, where rodents are exposed for the hawks to capture, or insects are uncovered after crop cutting.

Wildfires often attract foraging hawks, especially grass fires in their South American wintering range where they frequently wait around the edges of the fire, picking off insects and vertebrates including grouse, lizards, and snakes.

This weekend I will be on my way to our raptor observation peak high in the Wellsvilles hoping to see this amazing bird, along with a host of other raptors as they migrate to more favorable climes, but only one of the myriad species will make it all the way to Argentina!

This is Jack Greene reading for Wild About Utah.


Pictures: Courtesy US FWS, San Andres NWR
Text: Jack Greene, Bridgerland Audubon Society

Additional Reading:

Animal Fact Sheet: Ringtail, Arizona-Sonora Desert Museum, https://www.desertmuseum.org/kids/oz/long-fact-sheets/Ringtail.php

Ringtail (Bassariscus astutus), Wildscreen Arkive, https://www.arkive.org/ringtail/bassariscus-astutus/

William Swainson and His Namesake Hawk and Thrush

William Swainson and His Namesake Hawk and Thrush: Swainsons Thrush, Photo Copyright 2004 Jim Bailey
Swainson’s Thrush
Catharus ustulatus
Copyright © 2004 Jim Bailey

Swainsons Hawk, Buteo swainsoni, Photo Copyright 2010 Eric Peterson Swainsons Hawk
Buteo swainsoni
Copyright © 2010 Eric Peterson

What links this melodious thrush of northern Utah forests
(Kevin Colver: Song Birds of Yellowstone)
with a hawk that soars over farms, range lands and prairies in western North America?

Both Swainson’s Thrush and Swainson’s Hawk are named after the 17th century self-taught British naturalist, William Swainson. He was a contemporary of John James Audubon. Like Audubon, Swainson was a passionate solo collector, taxidermist and skilled illustrator of birds. Unlike Audubon, Swainson’s single intensive field expedition took him far to the south, sailing to eastern Brazil. During his two year stay, he amassed a collection of 20,000 animal specimens, including 760 bird skins. Swainson ultimately named 20 species new to science. Although he never visited North America, he nonetheless co-authored an encyclopedic four volume treatise about North America’s fauna.

Swainson’s Hawk and Swainson’s Thrush share another similarity, this one biological. Both birds migrate long distances to escape winter’s cold and hunger. Swainson’s Thrush winters in balmy tropical forests of South America. Swainson’s Hawk soars farther, all the way to the arid Argentine pampas. There this large slender hawk dines mostly on big flying insects, particularly grasshoppers and even dragonflies. Swainson’s Hawks migrate in groups, often along regular corridors. Every September, Hawkwatch volunteers and hardy birders have reported hundreds of Swainson’s Hawks rocketing past the Wellsville Mountains of northern Utah, flying amid several thousand migrating raptors of all kinds.

Birds migrate to avoid the snow, cold and lean times of northern winters. Migration poses natural risks, of course. Hawkwatch ornithologists also suspect that widespread use of two deadly organophosphate insecticides on Argentine crops kills many insect-eating Swainson’s Hawks. The plow, pavement and subdivisions have also reduced this hawk’s historic northern range, especially in California. In addition, foolish people still shoot this relatively tame hawk, not caring that its diet of rodents and grasshoppers benefits our farmers and ranchers.

Professional disappointments drove the quarrelsome William Swainson south as well, to New Zealand, where he died in anonymity. His namesakes, Swainson’s Hawk and Swainson’s Thrush, live on to cross and recross the equator in pursuit of perpetual summer and the feast it provides.

This is Linda Kervin for Bridgerland Audubon Society.

Pictures: Swainson’s Hawk, Courtesy and Copyright © 2010 Eric Peterson, as found on utahbirds.org
Swainson’s Thrush, Courtesy and Copyright © 2004 Jim Bailey, as found on utahbirds.org
Bird Recordings: Kevin Colver https://wildstore.wildsanctuary.com/collections/special-collections
Text: Jim Cane, https://bridgerlandaudubon.org/
Voice: Linda Kervin https://bridgerlandaudubon.org/

Additional Reading:

Swainson’s Hawk, Fieldguide, Utah Division of Wildlife Resources, Utah Department of Natural Resources, State of Utah, https://fieldguide.wildlife.utah.gov/?species=buteo%20swainsoni

Swainson’s Hawk, All About Birds, The Cornell Lab of Ornithology, https://www.allaboutbirds.org/guide/Swainsons_Hawk/overview

Swainson’s Thrush, Fieldguide, Utah Division of Wildlife Resources, Utah Department of Natural Resources, State of Utah, https://fieldguide.wildlife.utah.gov/?species=catharus%20ustulatus

Swainson’s Thrush, All About Birds, The Cornell Lab of Ornithology, https://www.allaboutbirds.org/guide/Swainsons_Thrush/