Early Migrant Warblers by Drew Weber
Migration may seem like it is just beginning, but some species are already moving south, and some have all but disappeared. Some of the earliest migrants are Cerulean Warbler, Hooded Warbler, Louisiana Waterthrush, Prairie Warbler, and Worm-eating Warbler. These species were already migrating south at the end of July, heading towards their wintering grounds. These species have all but disappeared from many parts of their breeding grounds already, and have completed vacated northern parts of their range.
If you want to find these species yet this year, there is time to get out and search for them but time is slipping away. Worm-eating Warblers are on their way to Mexico and Central American, while Cerulean Warblers are heading for high quality forests in the Andes. On a trip to Costa Rica in early August several years ago, I was surprised to find a Louisiana Waterthrush chipping along a stream, looking quite at home already.
The distances these birds fly between breeding and wintering grounds is quite stunning. The Louisiana Waterthrush that I saw in Costa Rica had just finished flying over 2,000 miles if it came from somewhere in Pennsylvania which is the central part of their range. To top it off, this 0.7 oz bird just flew across the Gulf of Mexico, possibly island-hopping from the Florida Keys thru Cuba and the Yucatan Peninsula in Mexico before arriving at this final destination.
In order to make their trip a bit easier, these long distant migrants are primarily making their flights at night when the air is more stable. Another advantage of migrating at night is that most of their predators are visual hunters and so the warblers are relatively safe at night. All night long while you are asleep, warblers and other migrants are streaming overhead, almost undetectable except for the occasional chip notes that alert us to their passing. These early migrating warblers are taking advantage of ample food supplies such as insects as they travel. A perk for us birders is that the birds then spend the day foraging to fatten up for the next leg of their journey. This makes them easier to find because they are actively moving around.
Once these birds reach their final wintering destination, they join up in mixed species flocks with other Neotropical migrants, as well as tropical species that live in Central and South America year round. In the tropics there are lush forests that have a bounty of food resources, enough for both the residents and the migrant warblers. A good question would be, “why don’t they just spend the entire year there if the food resources are so great?” The answer is that the food available to them at their breeding grounds is abundant as well, and they have likely evolved to migrate to both take advantage of these resources as well as avoid competition with the year round residents of the tropical forest.
So, the next time that you are out looking at birds and find a warbler, think about the journey that this tiny bird is about to embark on. With some good fortune, the same bird will be making the same journey back next year to nest again.