Excerpts from Jim Conrad's
Naturalist Newsletter

from the April 21, 2008 Newsletter written in the community of 28 de Junio, in the Central Valley 8 kms west of Pujiltic, elev. ~700m (2300ft), ~N16.331°, ~W92.472°; southeastern Chiapas state, MÉXICO
ARRIVAL OF THE SULFUR-BELLIED FLYCATCHER
Sulfur-bellied Flycatchers are fairly common, large, heavily striped flycatchers with long, rufous-colored tails. They're even found in the US, in canyons along the Mexican border where Arizona and New Mexico meet. I wouldn't mention my spotting one here except for two things:

First, for us this is a summer bird. In other words, the species winters in South America and comes north to Mexico and Central America during the northern summer. It's interesting to think about why the species migrates, simply changing one disturbed, tropical habitat for another. Is this a case of a migratory impulse evolving back in the Ice Age when it may have made sense, but now is merely a vestigial behavior providing little competitive advantage?

My guess is that this bird is taking advantage of the rainy season's greater abundance and diversity of winged insects. He's in South America during that continent's rainy season, and now has come to this side of the equator for our rainy season, shortly to begin. If this is the case, one wonders why more tropical species don't do it, and how did the species ever discover that when things dried out south of the Equator they were getting rained on to the north?

The second reason I'm glad to mention spotting this bird is that it's the hundredth species on my list of birds seen at 28 de Junio and its reserve. The list is available here.