Thursday, December 25, 2008

Weirdo warblers

After more than a week on the Golden-cheeked Warbler project here in Chiapas, and the goldencheek counter still only at one, it’s clear that we’re off to a poor start. I expected to have seen more of them by now. I thought I briefly saw one yesterday, but I got such lousy looks and the bird never reappeared, that I decided not to count it.

What I didn’t expect to see here was a Magnolia Warbler. For some reason, we’re not seeing many Golden-cheeked Warblers but we’re seeing these goofball warbler species that aren’t supposed to be here. Last week we had a male Black-throated Blue Warbler in one of the flocks. Yesterday, we found a Magnolia Warbler in the first flock we studied at our second site, Huitepec, in the mountains just outside of San Cristóbal.

Mind you, we’re not really out of wintering range for Magnolia Warbler here. But I have never seen one in warbler flocks in mesoamerican pine-oak forests, because those flocks are generally at elevations too high for Magnolia Warbler.

This species, according Cornell’s Birds of North America (1) , occurs on the wintering grounds in a variety of habitats between sea level and 1,500 masl. The bird we saw in Huitepec was in cloud forest, at an elevation of 2,351 masl!

Another thing that occurred to me while observing this flock: do certain flock members perhaps stick together? For example, the first birds we encountered in this flock were a female Black-and-white Warbler and a Slate-throated Redstart. Both are birds with very distinctive foraging styles; quite different, both however utilizing the same middle layer of the forest. During the two and a half hours that we observed this flock, these two would occasionally pop up, always together. Other duos we observed in this flock were the Magnolia Warbler paired with one of the three Blue-headed Vireos, and two female/immature type Townsend's Warblers. Seeing one member of these duos was usually followed by seeing the other.

This is not something I've observed or been aware of before, but – if true – could be an interesting aspect of flock dynamics. Such a phenomenon may be more pronounced in forests with dense vegetation, like for example this cloud forest at Huitepec, where visibility is limited, as compared to more open situations in classic pine-oak forest. What I have noticed before is that the area used by the flock tends to be smaller in forests with dense vegetation, and bigger in more open forest.

(1): Hall, George A. 1994. Magnolia Warbler (Dendroica magnolia), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

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