The Lower Rio Grande Valley is famous for
its spring migration: during the peak times of
mid-April to mid-May, if you get a good storm
front coming in from the north (stopping the
migrants in their tracks as they arrive after just
having crossed the Gulf of Mexico), the birding
can be fabulous! Fall birding isn't quite
as predictable (we don't get many storm fronts
coming up from the south, halting the southbound
migrants before they cross the Gulf), but
it can still be exciting!
One thing many people don't realize is that, for some birds, migration actually starts in midsummer! The shorebirds that nest in the high arctic arrive at the breeding grounds, raise their kids, and start south before the cold weather sets in, so they can show up here in the Valley in July, with peak numbers in August (Upland and Buff-breasted Sandpipers, Wilson's Phalarope), September (Semipalmated Plover and Sandpiper, Solitary Sandpiper, Whimbrel, Red Knot) and continuing well into October (Baird's and Pectoral Sandpipers). Many target shorebirds, such as Piping Plover, Long-billed Curlew, and Stilt Sandpiper, start showing up in August and then spend the winter with us, not heading north again until May or June!
The Bayside Flats at South Padre Island (located just north of the Convention Centre) is a great place to look for shorebirds as one can drive right up to them (a higher-clearance vehicle is recommended, however, as while the sand is pretty hard packed under the multiple big "puddles" that congregate between you and the birds, they can look rather intimidating)!
Back on the mainland, the nearby Port Isabel Reservoir on Holly Beach Road (just off FM 510) can be another great place to study shorebirds, depending on the water levels. If you haven't gotten enough of driving on the beach, a run down to Boca Chica Beach will allow for that, depending on the tides and surf (Note: Non-US citizens will need to show a passport at the Immigration Check Point), and north of the Island, at Port Mansfield, you can observe shorebirds from the comfort of their new sheltered overlooks.
Any of the myriad small wetlands and resacas can also be productive; a few of our favorites include the "SR 100 Resacas" located just west of the US77/SR100 intersection, the "Rangerville Resaca" south of Harlingen on Rangerville Road and just south of Jimenez Road, and the multiple ponds within Estero Llano Grande State Park. If the water is low enough, Delta Lake (off FM 88) and Sugarhouse Pond (off FM 1425 north of SR 107) can also be very good. For the "grasspipers", one of the best spots is the Superior Turf Farms (locally known as the Weaver Road Sod Farms), located just north of Jimenez Road; great viewing is had right from Weaver Road!
September is the big push for many land birds: Hawk migration is probably the most famous (the big push of Broad-winged Hawks takes place about that time, with lesser numbers of Mississippi Kites, and even more rarely Swallow-tailed Kites), and October is the peak for Swainson's Hawks and nightjars (seeing one of the latter is a challenge); Bentsen Rio Grande State Park holds weekly hawk watches during September, so this is a great time to learn raptor ID skills!
Songbirds such as Baltimore Orioles and Ruby-throated Hummingbirds can also come through in staggering numbers in September, along with smaller numbers of the expected migrant vireos. Almost all the migrant flycatchers are present in September, as well as many of our warblers (see below). Some of our migrants breed just north of the Valley, so expect Louisiana Waterthrushes and Orchard Orioles to show up as early as July!
Warblers such as Yellow-throated, Yellow, Worm-eating, Canada, Wilson's, and Yellowbreasted Chats start coming through in August, followed by Northern Parula, American Redstart, Northern Waterthrush, and Mourning Warbler in September. Some of the later migrant warblers, such as Ovenbird and Tennessee, Hooded, and Magnolia Warblers, won't pass through until October. As in spring, the Convention Centre on South Padre Island (along with the Birding and Nature Center) can be good places to look for migrant land birds, but in fall they can show up most anywhere, so checking out any of our wooded migrant traps such as Quinta Mazatlan in McAllen, Frontera Thicket in Weslaco, Santa Ana NWR in Alamo, or even Edinburg Scenic Wetlands should be worthwhile.
A great resource for finding out what occurs when is John Arvin's Birds of the South Texas Brushlands, a bar-graph checklist available online at Texas Parks and Wildlife.