Nebraskaland

56 Nebraskaland • October 2021 The term "migration spectacle" in the Great Plains usually conjures images of clouds of snow geese, swarms of sandhill cranes or hordes of red-winged blackbirds. Rarely is the term associated with a bird of prey in Nebraska. However, every autumn a mass migration of Swainson's hawks takes place during a very brief period. If you are not in the right place at the right time, it is easy to miss. Swainson's hawks are similar in size and structure to our resident red-tailed hawks, but one major diff erence is that Swainson's hawks undertake an extraordinarily long migration twice each year. Swainson's hawks spend the winter in southern South America, primarily on the Pampas grasslands of Argentina. In spring, this species migrates north through South and Central America to reach their breeding sites in the Great Plains and Intermountain West of North America. Some birds even nest as far north as the Yukon or eastern Alaska, which translates into a one-way migration of 7,000 miles or more. As summer fades and gives way to fall, Swainson's hawks must migrate back south to reach their winter quarters. In Nebraska, the main movement of Swainson's hawks occurs at the very end of September or during the fi rst few days of October, often on the heels of a cold front. On certain days, especially in central Nebraska, dozens of Swainson's hawks may be seen overhead or in open spaces, and sometimes groups can number into the hundreds or even low thousands. The largest groups are often observed in and around recently harvested soybean or corn fi elds where birds settle in to roost during the evening and are present the following morning before they continue south. Groups of these birds often will follow the combines in the hopes the disturbance exposes easy prey, such as mice, voles and grasshoppers — yes, these hawks readily consume large insects. If you are fortunate enough to encounter a fl ock of Swainson's hawks in the fall, take some time to appreciate the variation in their plumages. This species has light, rufous and dark phases or morphs. Light phase birds, which are usually the most numerous, have dark upperparts, a white belly, a brown bib on the upper breast and a white area on their head near the base of their bill. Dark phase birds are entirely dark brown, and intermediate birds are mostly dark, but also have variable rufous underparts. The Swainson's hawks' migration only becomes more spectacular as they move south, and birds are increasingly concentrated as the landmass narrows through Mexico and Central America. Like most raptors, Swainson's hawks rely on thermals of hot air that rise as the sun warms the ground. Migration over the ocean is not an option for these birds because there are no thermals. Flocks, or kettles as they often are called, may number into the hundreds of thousands until they reach South America. MIXED BAG RAPTOR MASS MIGRATION By Joel G. Jorgensen If you are fortunate enough to encounter a fl ock of Swainson's hawks in the fall, take some time to appreciate the variation in plumage of these birds. JOEL G. JORGENSEN, NEBRASKALAND

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