Patterns from eBird -- Gulf of Mexico migration
Blackpoll Warbler, St. Johns, Newfoundland, May. Photograph by Brian Sullivan.
The basic distinction is just as it sounds: some birds fly directly across the Gulf of Mexico, while others take a route that skirts the edge of the Gulf and allows them to avoid flying over open water. The evolutionary calculus that has led to these different strategies takes into account a couple different things. First, migration is an energetically costly and inherently risky enterprise. This is especially true over water. If bad weather strikes during a crossing, birds caught over open water may not be able to fly to safety. The birds that have evolved migration routes over land probably are safer, since they can easily weather a storm in some thicket or copse of trees anywhere along their path. On the other hand, the birds that find the shortest possible route need less overall energy to get from point A (wintering grounds) to point B (breeding grounds). These birds may also arrive more quickly, which means they can claim the best breeding territories in spring and the best wintering grounds when returning south in fall. Thus, the specific strategy employed by the various species depends on the species' breeding/wintering grounds, its physiological ability to fly long distances over water, and the complex interaction of the benefits of a shorter migration path over the costs of taking a riskier route.
In the discussion below, we provide animated STEM maps for a wide range of species. While many of these spring migration routes have been discussed in field guides and even textbooks, we are excited to display the animations of the migrations side-by-side for the first time. Instead of discussing each species' annual cycle in depth (these can all be found on the occurrence map pages), below we make quick comparisons about the spring migration routes of these spring migrants, just as we all eagerly await the first eBird reports in our area!
One failing of these maps is that the models have so far been built for the continental United States only. So you must use your imagination south of the border as you envision the departure of Scarlet Tanagers from the Yucatan Peninsula, or the flow of flycatchers northward along the Gulf Coast in Verzcruz and Tamaulipas, Mexico. Similarly, these models show bird occurrence on land, so the river of Neotropical migrants that pulses across the Gulf of Mexico is also not depicted.
Yellow-billed Cuckoo: A long-distance migrant that winters in South America, cuckoos are strong fliers. Much of the population heads up the Yucatan Peninsula and makes a direct crossing of the Gulf of Mexico. However, many birds breed in west Texas and a few breed west to Arizona, California, so these birds may take a more direct route up through Mexico. Notice how much later these western breeders arrive, with few records before late May. Read more.
Scissor-tailed Flycatcher: Wintering in southern Mexico and south to Costa Rica, Scissor-taileds breed far enough west that a trans-Gulf crossing would not gain them much. They tend to move coastally through eastern Mexico and enter the U.S. through south Texas. They are routinely seen on active diurnal migration in Texas. Read more. Yellow-throated Vireo: Yellow-throated Vireo winters from southern Mexico south to Colombia and breeds in the eastern U.S. and Canada. In classic trans-Gulf migrant fashion, it moves north through the Yucatan and undertakes a direct crossing of the Gulf when conditions are right. This is true for Red-eyed Vireo as well, but not for Warbling Vireo, which is a circum-Gulf migrant. This is a new map, with no occurrence map page yet.
Wood Thrush: Wood Thrushes winter from southern Mexico to Panama and on spring passage many of them undertake a direct trans-Gulf migration. Catharus thrushes (like Swainson's, Gray-cheeked, and Veery) take a similar route, and Gulf Coast thickets can be alive with the calls and sights of these brown thrushes, which otherwise can be quite hard to detect on migration. Read more.
Prothonotary Warbler: A brilliant yellow favorite of warbler-watchers everywhere, Prothonotaries winter in swampy woods from Mexico to northern South America. Like many eastern warblers, they are true trans-Gulf migrants, and their spring arrival on the mid-Gulf coast is pretty obvious on the occurrence map below. Read more. Chestnut-sided Warbler: Chestnut-sided Warbler winters from west Mexico south through Central America. Their northward passage is brings them up through south Texas and also north through the Yucatan. Like Orchard Oriole and many other species, Chestnut-sideds may employ both circum-Gulf and trans-Gulf strategies, depending primarily on where they are going and where they are coming from. Read more. Blackpoll Warbler: the migration route of Blackpoll Warbler has been much studied and debated. It winters in Amazonian South America and migrates south in fall over the open ocean, jumping straight from the Northeastern U.S. to the eastern Caribbean or even South America. The spring route is the reverse, but shifts to the west a bit, allowing the warblers to stop off on islands when needed, and with many birds coming north through peninsular Florida. Essentially unknown in Texas in fall, there are a few northbound Blackpolls that reach the Texas coast each spring, but never in the huge numbers seen in Florida and on the East Coast. Read more. Scarlet Tanager: Wintering in Amazonian South America, Scarlet Tanagers breed in the eastern U.S. and eastern Canada and are classic trans-Gulf migrants. The concentration of recent arrivals on the coast of Louisiana and east Texas shows up quite obviously on the occurrence map below, and makes it apparent just how important these coastal areas are to tired migrants! Read more. Indigo Bunting: Although a few Indigo Buntings winter in south Texas, most winter to the south in Mexico and Central America. In spring they come north via both routes: both over and around the Gulf. In reality, many species show this flexibility, and categorizing birds as either trans-Gulf or circum-Gulf is not always black-and-white. Read more. Bobolink: Bobolink winters in southern South America and migrates north to eastern South America, embarking from there on a flight across the eastern Caribbean with occasional stops on the islands. The population enters the U.S. in Florida and other eastern states, and is actually comparatively rare in Texas. Several other Caribbean species, including Black-throated Blue Warbler, Cape May Warbler, and others follow a similar route, mostly avoiding the western Gulf. Read more.
