Swainson’s hawks are medium-sized hawks that breed in western North America and winter primarily in southern South America. Here are some key facts about where these migratory raptors spend their winters:
What areas do Swainson’s hawks migrate to in the winter?
The majority of Swainson’s hawks winter in the Pampas regions of southern Brazil, Uruguay, and central Argentina. This expansive grassland habitat provides an abundance of insects, small mammals, and reptiles for the hawks to prey on during the winter months.
Research has shown around 95% of Swainson’s hawks migrate to and winter in a fairly concentrated area spanning parts of southern Brazil, Uruguay, Paraguay, and northern and central Argentina.
Country | Main wintering regions |
---|---|
Brazil | Rio Grande do Sul |
Uruguay | Across western and southern regions |
Paraguay | Southern and western regions |
Argentina | Buenos Aires, La Pampa, San Luis, Cordoba, Santa Fe, Entre Rios, Corrientes |
A smaller number, around 5%, overwinter in the Llanos regions of Colombia and Venezuela. The Llanos is a vast tropical grassland plain, similar to the Pampas, that also provides plentiful prey for the hawks.
How far do Swainson’s hawks migrate?
Swainson’s hawks make one of the longest migrations of any North American raptor. They can travel up to 14,000 miles round trip each year between their breeding grounds in western North America and wintering grounds in South America.
Their southbound migration from the U.S. and Canada to Argentina covers approximately 5,000 – 8,000 miles one-way. The return trip north covers another 5,000 – 8,000 miles back to their breeding territories.
What routes do they follow?
Swainson’s hawks generally follow well-defined flyways on their epic migrations between North and South America:
- Autumn migration south: They concentrate along the front range of the Rocky Mountains in late summer and begin migrating south through Central America or Mexico in September. Some hawks follow the Atlantic coast south from Florida.
- Spring migration north: They return to North America through Central America or Mexico starting in March. Raptors spread out across the western U.S. to reach breeding grounds from Alaska to northern Mexico.
When do Swainson’s hawks arrive on the wintering grounds?
Most Swainson’s hawks arrive on their South American wintering grounds between mid-October and December. The timing of migration depends on the following factors:
- Age – Adult hawks tend to start migrating earlier and arrive in Argentina and surrounding regions in October and November. Young hawks migrating for the first time arrive later, in November and December.
- Weather – Migration tends to be earlier in warm autumns with beneficial winds and later if poor weather causes delays.
- Breeding ground location – Swainson’s hawks from farther north in Canada migrate through the Great Plains and arrive in South America later.
By mid-December the bulk of the population has reached the grasslands regions of southern Brazil, Paraguay, Uruguay and central Argentina where they’ll spend the next 6-7 months.
How long do they stay on the wintering grounds?
Most Swainson’s hawks remain on their South American wintering grounds for around 6 to 7 months. They start arriving in October and November, and most birds depart for the return migration by March and early April.
Some data suggests older, more experienced adult hawks spend the shortest time on the wintering grounds and are the first to start migrating north again by February and March. Younger hawks, less than 5 years old, may overwinter for a month longer before beginning spring migration in April.
What habitats do Swainson’s hawks use in South America?
Swainson’s hawks occupy open grassland and pastureland habitats during the winter months in South America. The main habitat types they utilize are:
The Pampas
The majority of the population winters in the expansive Pampas grasslands that span northeast Argentina, Uruguay, and southern Brazil. This fertile plain covers over 750,000 square km and provides ideal habitat of open grasslands and farm fields with abundant prey.
The Llanos
A smaller number of Swainson’s hawks overwinter in the Llanos region of northern Colombia and Venezuela. The Llanos is a vast tropical grassland plain covering over 300,000 square km, made up of treeless open savannas, wetlands, and pastures.
Agricultural lands
Swainson’s hawks often forage in agricultural areas, particularly alfalfa, wheat, and soybean croplands in the Pampas region where rodent prey tend to be abundant.
Ranchlands
Pasturelands and grasslands grazed by cattle provide an important habitat, offering prey like rabbits, ground squirrels, mice and insects.
What do Swainson’s hawks eat in South America?
Swainson’s hawks are opportunistic predators that hunt a wide variety of small prey on their wintering grounds in South America. Their main prey includes:
- Insects – especially grasshoppers, cicadas, beetles
- Small mammals – mice, rats, ground squirrels, voles
- Reptiles – lizards, snakes
- Birds – doves, sparrows, blackbirds
- Rabbits
In grasslands and ranchlands, they typically hunt mice, ground squirrels, rabbits, reptiles, and grasshoppers. In agricultural areas, rodents like voles, rats, and mice make up a large portion of their diet.
Hunting techniques
Swainson’s hawks employ a variety of hunting techniques to capture prey on their wintering grounds, including:
- Still-hunting – Perching and scanning for prey from an elevated perch
- Low-flying coursing – Gliding and flying low over grasslands to surprise prey on the ground
- High-flying – Soaring at heights up to 1000 feet to spot prey below
- Hovering – Hovering in midair while hunting
- On foot – Walking on the ground to chase down prey
Do Swainson’s hawks compete with other raptors in South America?
Swainson’s hawks overlap on the wintering grounds with several resident raptor species, but generally do not compete strongly with them for prey and habitat resources. The other main raptors they share habitat with include:
Species | Diet | Habitat |
---|---|---|
Chimango caracara | Insects, small mammals | Open grasslands |
White-tailed kite | Small mammals, birds | Grasslands, farm fields |
Aplomado falcon | Birds, insects | Savanna, grasslands |
Differences in preferred prey and foraging habitat allow Swainson’s hawks to winter alongside smaller numbers of these resident raptors without substantial competition.
Do they mix with other hawk species?
Swainson’s hawks are sometimes seen feeding or roosting in mixed flocks with other migratory hawk species from North America that also overwinter in South America, such as:
- Broad-winged hawk
- Short-tailed hawk
- Zone-tailed hawk
- Red-tailed hawk
- Sharp-shinned hawk
However, Swainson’s tend to remain mostly separate from these other species on the wintering grounds.
How do Swainson’s hawks behave and communicate on the wintering grounds?
Swainson’s hawks exhibit the following behaviors and communication on their wintering territories:
Foraging
They hunt both solo and in pairs over open grasslands and agricultural fields.
Roosting
They roost communally in groups up to 20-30 hawks, choosing sites with lots of trees such as windbreaks, tree lines, small woodlots, and forest edges.
Vocalizations
Swainson’s hawks make rattling high-pitched alarm calls to alert others to danger. They communicate with a high whistled “klee-uk” courtship call.
Displays
Breeding displays like circling flights and undulating displays help pairs reestablish bonds before migrating north to nest.
Interactions
They have occasional antagonistic interactions with other hawks over territorial disputes or prey theft.
What threats do Swainson’s hawks face on the wintering grounds?
Some key threats to Swainson’s hawks in their wintering areas include:
- Habitat loss – Conversion of native grasslands to agriculture reduces habitat.
- Poisoning – Pesticides reduce prey and can poison hawks.
- Human persecution – Shooting, trapping, etc.
- Collisions – Power lines, towers, turbines, and vehicles.
Habitat loss to cropland expansion is the greatest threat, as it shrinks the open grasslands favored by Swainson’s hawks for winter foraging.
Is climate change affecting them?
Some potential climate change impacts on wintering Swainson’s hawks may include:
- Shifting wintering ranges as habitats change
- Impacts on prey abundance and distributions
- Increased drought drying out grasslands
- Weather pattern changes altering migration timing
Ongoing research is studying how climate shifts may influence Swainson’s hawks on their South American wintering grounds in the future.
Conclusion
Swainson’s hawks undertake an incredible 14,000 mile round trip migratory journey each year between their breeding territories in western North America and wintering grounds in the grasslands of southern South America. On wintering areas spanning parts of Argentina, Brazil, Uruguay, and surrounding regions, Swainson’s hawks occupy open pasture and grassland habitats where they hunt rodents, rabbits, insects, reptiles and other small prey. Though they face threats from habitat conversion and pesticide use, most Swainson’s hawks successfully overwinter and make the return trip north to breed in the springtime.