3 September 2010 – two warblers

Last night (Thursday), our recent intense heat and humidity (108 heat index on Sep. 1) broke in a major way with a powerful gust front and storm system. A straight line wind speed of 87 mph was recorded in Oklahoma City. Overnight the temperature dropped considerably, and temperatures were in the upper 50s with a north breeze this morning. That weather seems to have finally brought down some migrants from the North.

I found two birds this morning, and both represented identification challenges. The first was an immature Mourning Warbler:

This bird’s throat was actually pretty grayish-white, rather than the obvious yellow one might expect on this species. Thus, I considered very carefully whether it might be a MacGillivray’s Warbler. But the broken eye-ring on this bird was barely broken, extending closer to the “corners” of the eye than typical for MacGillivray’s. Also, the undertail coverts extended very near to the tail tip, as expected for Mourning. Thus despeite the lack of a clear yellow throat, I’m confident calling this bird a Mourning Warbler.

I’m also confident in describing it as a fat score = 3. The bird’s fat completely filled the furcular hollow and extended over a large portion of the breast. The fat can be seen in the following photo right through the bird’s relatively transparent skin. The breast skin of a bird without a fat deposit would look sort of brick red in color, kind of like dark meat on a chicken. On this bird, the off-white color of subcutaneous fat is obvious:

The next bird was represented only by a few remiges:

These were smaller than the primaries on the Mourning Warbler, and rather dark gray with just a slight edge of olive green. The size, color, and lack of pattern indicate “warbler” to me, but it will have to be listed as “unknown.”

In this case, both birds hit the building after it stopped raining last night (~ 9 pm), judging from the excellent condition of the feathers. One was scavenged in that time – but still obvious to me – and one was untouched. The specimens were found about 7m from each other on the north side of the building.

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