Prof. W. W. Cooke (1904) writes: “Though in migration the yellow warbler occurs in Florida as far south as Key West and is sometimes fairly common in northern Florida, the numbers that migrate through the southern part of the State must be very small, for not a bird passing north or south has been reported from any of the Florida lighthouses. The migration route of the yellow warblers that breed near the Atlantic coast is evidently southwest to northern Georgia and Alabama, and then across the Gulf of Mexico.”
Perhaps the main flight from Florida and the other Gulf States is across the Gulf to Yucatán and then down through Central to South America, for there seem to be no records for Cuba for the eastern yellow warbler. There is a regular migration along the coast of Texas. Dickey and van Rossem (1938) say that “the eastern yellow warbler migrates through El Salvador in fair numbers, but no specimens were taken at any time during the winter. In the fall, particularly, great numbers are in evidence. The first arrivals reached Lake Olomega on August 1, but the main body did not begin to drift through until about the middle of that month.”
Frederick C. Lincoln (1939) remarks: “Redstarts and Yellow Warblers, doubtless the more southern breeders in each case, have been seen returning southward on the northern coast of South America just about the time that the earliest of those breeding in the North have reached Florida on their way to winter quarters.”
Winter.—Dr. Alexander F. Skutch contributes the following winter notes: “This morning as I sat at breakfast a yellow warbler flitted among the shrubbery outside the window. Here in Central America, through 8 or 9 months out of the 12, this well-known bird occupies the same place in dooryard, garden, hedgerow and scrubby pasture as during its briefer sojourn in the more northerly regions where it nests. None of the resident warblers of Central America is quite so abundant and familiar about human dwellings. Everywhere it avoids the heavy forest and prefers the sunlight that floods the clearings made by man.
“It is one of the first of the visitants from the North to arrive in Central America, appearing in Guatemala as early as August 9, reaching Honduras by at least the fourteenth, Costa Rica by the seventeenth, and Panamá by the twenty-second of the month. These early dates are for the Caribbean lowlands, along which it appears to migrate. It arrives later on the Pacific side of the Isthmus, especially in Costa Rica, where it has not been recorded before August 24, at San José, and not until September 11 in the Térraba Valley, still more isolated from the Caribbean flyway by lofty, forested mountains. But by the end of September, it is well distributed as a winter resident over both coasts of Central America, and in the interior up to at least 5,000 feet, becoming rarer at the upper limit of its altitudinal range. Much above 5,000 feet it apparently does not winter; but it is occasionally seen in September in the high mountains as a bird of passage. A heat-loving warbler, it is most common in the lowlands where, in the plantation districts of northern Central America during the winter months, it is among the most abundant birds, whether resident or migratory.
“Although a number of wood warblers which winter in the Central American highlands are gregarious, those that center in the lowlands are typically solitary. In this, the yellow warbler is no exception. Each wintering bird appears to have its own territory, from which it attempts to drive others of its kind. Trespassers are scolded with insistent chips; or more rarely, soon after his arrival, a male will sing while defending his claim. Near San Miguel de Desamparados, Costa Rica (4,600 feet), on October 1, 1935, I made the following note: ‘This morning, which for a change was bright and calm, I heard a yellow warbler singing in the low fig trees near the house. Upon going out to look, I found that there were two yellow warblers in the trees. One was trying to drive the other away; but the pursued always circled around and returned. I watched them for a long time; but this indecisive action continued without any change in the situation. In the intervals of the pursuit, the warblers (or at least one of them) would sing, but in a low and imperfect fashion, far inferior to the yellow warbler’s summer song.’ Again, on October 31: ‘After the Wilson warbler, the most abundant winter visitor is the yellow warbler. The bird who on October 1 drove its competitor out of the fig trees beside the house still retains these trees and the surrounding Inga trees as its domain.‘
“The yellow warbler sings far less while in Central America than many other wintering species. Exceptionally, one will be found singing profusely. In early October, 1934, I came upon such a bird among the coffee groves of a great plantation on the lower Pacific slope of Guatemala. His behavior was so far out of the ordinary that I am tempted to copy in full the notes I made upon it at the time: October 5—On the afternoon of my arrival at ‘Dolores,’ I went out for a walk through the coffee groves. From among the ‘chalum’ (Inga) trees which shaded the coffee bushes, I heard a bird’s song which seemed to belong to a warbler; but I did not recognize it as the utterance of any species I knew. After searching for a time among the tree-tops, I spotted the singer, and was surprised to find him a yellow warbler. He was apparently a young bird, for he lacked the chestnut splashes along the sides which distinguish the mature males. He repeated over and over again his little song of four or five notes, which was so unlike the familiar song of the yellow warbler in the eastern United States that I did not at first recognize it; but once I had identified the singer, I realized that I was listening to a shortened and modified form of the typical song.
“As I stood watching and listening to this eccentric warbler, the rain clouds which had been gathering darkly in the west began to surrender their pent-up waters; and the sudden shower approached across the plantation with the roar of a myriad fat drops striking against the large leaves of the Ingas and the far larger ones of the bananas which shaded the plantation. I took refuge from the rain beneath the broad expanse of a banana leaf, which completely shielded me from the beating downpour. Soon the heavy shower exhausted itself; and I emerged from beneath my green roof. The warbler, who had taken shelter from the shower somewhere in the foliage above me, resumed his cheerful singing.
“‘On the next two days, I passed by the spot where I had heard the warbler singing, on the way to and from my botanical collecting ground. Morning and afternoon, I heard the same voice in the same part of the coffee plantation, where the bird seemed to have fixed his residence.’