South Texas Fall Hawk Migration: Broad-winged Kettles at Bentsen
Every September, one of North America's most spectacular wildlife events unfolds over the Rio Grande Valley. Tens of thousands of raptors — led by the Broad-winged Hawk — compress into a narrow corridor along the Texas coast as they funnel south toward their wintering grounds in Central and South America. On peak days at Bentsen–Rio Grande Valley State Park, a single thermal can hold 10,000 or more birds spiraling upward in a dense rotating column before breaking off to glide south on set wings.
The Mechanics of a Kettle
Raptors are poor sustained flappers — they migrate by soaring, using thermals (rising columns of warm air) to gain altitude, then gliding southward to the next thermal. When a thermal coincides with a geographic pinch point, hundreds or thousands of birds converge in the same column. This swirling mass is called a kettle, named for the visual resemblance to boiling water.
South Texas is one of those pinch points. The Gulf of Mexico to the east and the Sierra Madre to the west funnel raptors through a relatively narrow coastal corridor. Add the topographic lift from the escarpment above the Valley floor and the result is some of the densest raptor concentrations anywhere on the continent during September and October.
What to Expect by Month
- August (late): The first wave belongs to the Swallow-tailed Kite, which begins moving south from its Florida and southeastern U.S. breeding grounds as early as mid-July. By late August, staging flocks of dozens to hundreds appear over the Valley before pushing across the Gulf.
- September (peak Broadwing week):The Broad-winged Hawk migration peaks during the third week of September — typically September 18–25 — though exact timing shifts year to year with weather. A cold front with northwest winds is the trigger: on the right morning, Bentsen's hawk tower can host counts of 10,000–30,000 Broad-wingeds between 10 a.m. and 4 p.m.
- October:Broad-wingeds thin out and buteos take over — Red-tailed, Swainson's, and Ferruginous Hawks move through, along with Osprey, Peregrine Falcon, and Aplomado Falcon. The local Crested Caracara and White-tailed Hawk remain on their territories year-round, providing a striking contrast to the migrants above.
Where to Watch in the Rio Grande Valley
Bentsen–Rio Grande Valley State Parkis the go-to hawk watch site in the Valley. The hawk tower — a 30-foot elevated platform near the park's west end — puts observers above the canopy, where scanning the sky is unobstructed. Arrive by 9 a.m. on days with northwest winds following a cold front. The park's tram service runs to the tower, or it's a short walk on flat trail.
Hazel Bazemore County Parkin Corpus Christi, roughly 100 miles northeast of the Valley, hosts the region's most systematic hawk count. The annual Rio Grande Valley Hawkwatch runs from mid-September through October, with volunteer counters tallying every individual. The park's 2024 season recorded over 700,000 raptors — making it one of the top hawk watch sites in North America.
Any open-country location with a clear view of the sky — a county road pull-off, a levee top, the parking lot of a nature center — can produce kettles during peak migration days. The birds are not restricted to a narrow flight line; the entire Valley corridor becomes a river of raptors when conditions align.
The Hook-billed Kite Factor
While counting Broad-winged Hawks by the thousand, alert observers at Bentsen sometimes pick out the much rarer Hook-billed Kite — a resident specialty of the Valley's mature woodland. Hook-billed Kites do not migrate; they live year-round in a handful of territories along the lower Rio Grande. But September and October hawk watches are the most productive time to see them in flight, as the birds often become active and soar during the same thermal conditions that lift the migrating Broad-wingeds. A close scan of any kettle at Bentsen is worth doing: the Hook-billed's distinctive bulging pale underwing and paddle-shaped tail silhouette are unmistakable once you know to look.
Planning Your Visit
- Best date range: September 18–25 for peak Broad-winged numbers; September 1–October 15 for the full migration season
- Best conditions: Clear sky with northwest wind following a cold front passage; thermals develop after 9–10 a.m.
- What to bring: Binoculars (8×42 is ideal for tracking distant kettles), a wide-angle spotting scope if you have one, and water — September in the Valley is still hot
- Bentsen tips: Park at the visitor center and take the tram or walk to the hawk tower; the park opens at 7 a.m. and fills up on peak days — arrive early