North and South: The Swainson's Hawk

This week, Swainson's Hawks will begin to arrive in the northern U.S.

Read on to learn about their migration and nesting habits!

Soaring high above the ground, numerous hawks dot the blue sky like so many kites. These hawks are Swainson’s Hawks. They are braving the perils of one of the longest journeys of any American hawk in order to successfully raise the next generations of Buteo Swainsoni, which is the scientific name of this hawk. In 1827, William Swainson first illustrated a Swainson’s Hawk, but it was not named after him until 1832 when a nephew of Napoleon Bonaparte discovered that this little-known hawk was a new species. The Swainson’s Hawk has an incredible life cycle, which includes a lengthy migration and a fascinating breeding season. Regrettably, there are numerous perils that threaten the life cycle of this species.

After a long spring migration from South America, the majority of the Swainson’s Hawks make their homes in the plains and prairie lands of western North America, where they breed and raise their young throughout the summer months. When fall comes, the hawks gather together in vast flocks, called “kettles,” in order to make the lengthy migration back to South America. Along the way, the Swainson’s Hawks may flock together with other migratory raptors, such as Turkey Vultures and Broad-winged Hawks. Flying in immense kettles, hundreds of thousands of Swainson’s Hawks can be viewed at a single location in Mexico in just one day during their migration! Eventually, the hawks reach Argentina, Paraguay, or southern Brazil, where they take up residence in the pampas, the South American grasslands. It is here that most of the hawks spend their winter from October to March. Some Swainson’s Hawks do not fly all the way to South America, but they winter in California, Florida, or southern Texas instead. The round-trip migration from North America to South America is over 12,000 miles, one of the lengthiest trips of a bird of prey on these continents. In March the hawks make the incredibly long journey again because they must be back in North America for their breeding and nesting season, starting in April.

A male Swainson's Hawk tours his territory from the air.

Arriving first on his summer stomping grounds, the male Swainson’s Hawk carefully selects a suitable nest site, or returns to a previous nest. Once the female joins her mate, the pair begins to construct their nest using materials like thin sticks, dead weeds, and soft bark. Most Swainson’s Hawks build their nests on a tree branch at least ten feet above the ground; however, some may even build a nest on top of an old Black-billed Magpie’s nest! After mating and laying two to three eggs, the female incubates her incarcerated offspring while the male hunts and brings food back to the nest. Because of the increased number of beaks to feed after the chicks hatch, the adult hawks generally feed snakes, rodents, or small birds to their hungry children, who require a high-protein diet.

A pair of juvenile Swainson's Hawks with their mother in the nest.

Finally, after thirty-five to forty-four days in their cramped nest, the chicks will become fledglings and leave the nest. At first, the fledglings learn to catch their own food by hunting insects on the ground. The young hawks grow in their independence as time goes on, and they usually remain with their parents until their fall migration.

An immature Swainson's Hawk flies near its old nest.

Throughout the year, there are many dangers that threaten the Swainson’s Hawks. When they are in South America for the winter, some may be killed for their meat, while others may die from ingesting pesticides. In the 1990s, there was a sharp decline in the breeding population of the Swainson’s Hawks in North America because of widespread pesticide use in Argentina. Sadly, around 35,000 hawks died in one winter season; however, due to the diligence of international conservation organizations, use of the offending pesticide was halted, allowing the Swainson’s Hawk population to stabilize. Although that crisis was tempered, other issues persist, like grasshopper control programs, which reduce foraging habitat for the Swainson’s Hawks. Predators contribute to the decline of breeding pairs and their habitat by eliminating nestlings. Declining nesting activity has also been traced to the removal of vital nesting trees in grasslands or similar habitats. There is good news! It has been discovered that artificial nesting platforms have been used by Swainson’s Hawks in areas with few trees, and this has happily increased their breeding range. Similar solutions should serve to counter the threats that face the Swainson’s Hawks.

A female Swainson's Hawk stands guard over her nest.

As has been seen, Swainson’s Hawks are wonderful raptors with intriguing life stages that are worth protecting, whether the hawks are migrating or nesting. It is up to us. We have been given stewardship of the earth and its creatures by God, who made it all. Accordingly, we must take excellent care of His valuable creation. Whether it is breeding in the North or wintering in the South, the Swainson’s Hawk is clearly a wonderful wonder of God’s world.