COASTAL FALL-OUTS OF NEOTROPICAL MIGRANTS
A straight flight across the Gulf of Mexico is approximately 600 miles. During spring migration most birds flying north must accomplish this feat in a single non-stop flight or risk perishing. With a tail wind from the south, the flight may take only 24 hours. Under these favorable conditions, most birds can cross the Gulf and even continue some distance inland before dropping out to rest and feed. However, coastal habitats are crucial to birds which become exhausted by their northward flight across the Gulf of Mexico, or to those which encounter bad weather.
What is a “fall out”
On the coast, migrating birds “fall-out” or land in great numbers during or following inclement weather associated with a cold front. The passage of storms produces strong northerly headwinds. Flying against a strong head wind not only slows northward progress, but it takes much more energy to travel the same distance. In addition, cold dense sinking air currents actually push these birds down. Exhausted birds are forced to land and rest, often at the first patch of beach grass or woodlot.
Local birdwatchers know that cheniers (coastal woodlands dominated by live oak) can be exciting places to be during fall-outs. Because cheniers are “islands” of terrestrial habitat surrounded by expanses of marsh or water, they tend to concentrate birds. Cheniers provide shelter, food and fresh water for migrating birds as they arrive along the coast.
After a strong cold front, birds can sometimes be seen flying towards land just above the wave tops. Tired birds sometimes even land on the sandy beach. The wooded cheniers and their weedy edges soon fill with birds seeking rest, food, and water, including many species of colorful Neotropical migrants (such as warblers, tanagers, thrushes, and orioles). Larger birds also fall-out, and chenier treetops may provide temporary refuge for Green Herons, Yellow-crowned Night-Herons, Least Bitterns, and even Purple Gallinules which simply couldn’t make it any farther inland! During the most spectacular fall-outs, an observer can see many individuals of many different species of birds in colorful breeding plumage! It is not uncommon to tally 20 or more species of warblers in a day-- many in the same tree!
The timing of a cold front will usually dictate the diversity of migrants that might be expected to fall-out, depending on whether it occurs relatively early or late during spring migration. Typically, during any particular fall-out, a few species will dominate. Expected species composition will change as spring migration progresses. The greatest diversity of migrants occurs during mid-April to mid-May (although strong cold fronts become less frequent as spring progresses). Check the weather before you head out, because on a typical day with clear skies and southerly winds (good migrating weather) most migrants continue past the coast to points further inland such as the Atchafalaya and Pearl River basins, and few birds will be found in the cheniers.
Depending on how much their fat reserves have been depleted, migrants will linger on the coast for only a few hours or a few days, just long enough to rest and refuel before weather conditions become favorable for them to resume their northward journey toward their final destinations. So, fall-out events tend to be of short duration.
On the America’s WETLAND Birding Trail, both the Sabine (Loop 1) and Grand Isle (Loop 9) loops access the immediate coast. Popular places to check on the Sabine Loop (Loop 1) include the trees around the Sabine National Wildlife Refuge Headquarters and Visitor Center (Site 1-5), and the Peveto Woods Bird and Butterfly Sanctuary (Site 1-9), but any patch of vegetation on the immediate coast may harbor migrants. The Grand Isle Loop (Loop 9) offers many different wooded sites to explore.
The most frequently encountered migrant land birds in the cheniers during a fall-out in April include: Yellow-billed Cuckoo, Ruby-throated Hummingbird, Acadian Flycatcher, Eastern Wood-Pewee, Great Crested Flycatcher, Red-eyed Vireo, Yellow-throated Vireo, White-eyed Vireo, Wood Thrush, Gray-cheeked Thrush, Swainson’s Thrush, Veery, Gray Catbird, Blue-winged Warbler, Tennessee Warbler, Northern Parula, Yellow Warbler, Chestnut-sided Warbler, Magnolia Warbler, Yellow-rumped Warbler, Black-throated Green Warbler, Blackburnian Warbler, Yellow-throated Warbler, Palm Warbler, Bay-breasted Warbler, Blackpoll Warbler, Black-and-white Warbler, American Redstart, Prothonotary Warbler, Worm-eating Warbler, Ovenbird, Northern Waterthrush, Kentucky Warbler, Common Yellowthroat, Hooded Warbler, Yellow-breasted Chat, Summer Tanager, Scarlet Tanager, Rose-breasted Grosbeak, Blue Grosbeak, Indigo Bunting, Painted Bunting, Baltimore Oriole, and Orchard Oriole. Some are more secretive than others.
Less commonly encountered but still not unexpected in April: Black-billed Cuckoo, Philadelphia Vireo, Golden-winged Warbler, Cerulean Warbler, Cape May Warbler, Swainson’s Warbler, Louisiana Waterthrush, and Lincoln’s Sparrow.
Migrants commonly spotted in more open areas include Eastern Kingbird, Scissor-tailed Flycatcher, Dickcissel, and Bobolink; less commonly, Western Kingbird and Yellow-headed Blackbird.