For the Birds Radio Program: Tropical Migrants
Costa Rica—Northern Visitors
I’ve been to Costa Rica twice, and Trinidad and Tobago once. Of the 577 kinds of birds I saw in the tropics, only 138 were species I’ve ever seen anywhere else. This number includes quite a few Texas and Arizona specialties. The Scissor-tailed Flycatchers I saw in the Pacific lowlands of Costa Rica would return to Texas and Oklahoma the next spring. The abundant Kiskadee flycatchers—big, striking yellow breasted birds—and Pauraques—long-tailed tropical relatives of the Whip-poor-will, I originally saw in Texas, along with another abundant species, the Great-tailed Grackle. One tropical hummingbird that got lost up in La Crosse, Wisconsin, a couple of years ago, a Green Violet-ear, was abundant in the highlands of Costa Rica. But other than tropical species that don’t make it much farther than the Mexican border, overall there weren’t many familiar faces among the Costa Rican birds, making the ones I did see all the more treasured. I saw Summer, Scarlet, and Western Tanagers in April on my second trip to Costa Rica—they were wending their way through Central America on their way north from their South American wintering grounds. And I saw a good assortment of warblers on both trips to Costa Rica, where they were wintering.
On the long flight down on my first trip, I marveled from the plane about just how far away Costa Rica is. Imagine a Tennessee Warbler weighing a third of an ounce, or a Ruby-throated Hummingbird weighing a mere tenth of an ounce, flying all that distance on its own power, wingbeat after wingbeat, hour after hour, day after day, with no steel-clad airplane for protection, only a thin layer of tiny, iridescent feathers. I saw one Ruby-throat in Costa Rica. Many of them go only as far as Mexico, but some of these microscopic birds go even farther—some as far as northern South America. Exactly opposite of what you’d expect, the individual migrants that winter the farthest south tend not to be the ones that summered the farthest south. Instead of a species as a whole just shifting down the map, it turns out that the individuals that winter the farthest south tend to be the ones that summer the farthest north—those individuals may travel more than twice as far each migration as the ones that summer farther south and winter farther north. This leap-frog migration makes our northern birds’ journeys even more impressive.
Costa Rica may not be the center of hummingbird migration—that’s up in Mexico—but it IS the center for wintering Tennessee and Chestnut-sided Warblers, Philadelphia Vireos, and Baltimore Orioles. The vireos were abundant in the highlands, and the other species at almost every place I visited. The two warblers and the vireo were found individually or within small mixed flocks with tanagers, flycatchers and other warblers and vireos, but the orioles hung out in oriole flocks. Some had only ten or twenty orioles, others more than a hundred. Like other members of the blackbird family, Baltimore Oriole males don’t molt out of their brilliant feathers in winter, so these flocks were beautiful to see, lighting up trees with a fiery glow. I also saw a handful of Wood Thrushes, and snatched a quick look at a Swainson’s Thrush as it flew away.
Considering how many tropical birds fill these countries, defending their territories and food supplies, it’s amazing to me that our northern birds, which breed throughout an enormous range of the northern and eastern states and Canada, can funnel down to an area much smaller in size, already teeming with birds, and eke out an existence. It’s one of the miracles of the earth, one that gives us a lovely sense of the rhythms of our northern seasons, and gave me a fresh yearning to see this spring migration, when some of these familiar faces will reappear back home where I’m used to seeing them.