Thursday, May 26, 2011

The Black-throated Green (BTG) Warbler

One of the common traits of elementary school children and professional systems engineers is that they both tend to be chronic observers.  And both can be encouraged to express their opinions regarding their observations, especially to those that show an honest interest in their words.  Enter a classroom of 4th graders, and you will hear a free-flowing sharing of opinions as to why birds, and their offspring, repeatedly migrate over the same geographic areas (even if the 4th graders haven’t yet studied the topic).  Enter a conference room of systems engineers, and you will hear a free-flowing sharing of opinions on how best to launch a crewed aircraft (even if the engineers are not rocket scientists).
And, in my opinion, both 4th grader and system engineer are excellent at drawing subjective conclusions, given little objective evidence; and both will be honest about their conclusions being “a best guess.”  In contrast, ask a software engineer to hazard a guess about anything, and they will ask you to state the requirements for the problem.
I would love to fill a room with ten 4th graders and ten systems engineers, provide each with a drawing pad and box of crayons, and (after ensuring that none had any experience with birding or ornithological knowledge), ask each to draw a picture of a Black-throated Green Warbler.
And, my subjective conclusion, based on NO objective evidence, is that I would see 20 similar pictures, with variations due mainly to the creativity and artistic skills of the individual (and on average, the 4th graders may outperform in the artistic domain).  I can visualize 20 pictures that show varying sizes and shapes of green birds with black throats.  Some pictures may show a bird that is forest green, others lime green; some throats may be solid black, others striped horizontal or vertical, but, well, you get the picture.
And so if I post the following two pictures, the 20 will say, “You asked us to draw a green bird that is black-throated, and now you are showing us more pictures of the Golden-cheeked Warbler, and you just blogged about it!” 
 Photo 1:

Photo 2:

But look again, I would say, and follow your outstanding objective observation skills, as I repost one of the Golden-cheeked Warbler pictures for comparison.
The Golden-cheeked Warbler photo from May 20th blog:  "THE Native Texan":

The Golden-cheeked has a black eye line (with no other shadowing on its bright golden cheek); black crown, nape and mantle (back of neck and upper back); and all of these black areas appear equivalent regarding the saturation of “blackness”.  Also note that the breast, belly and vent (think underbelly behind the legs) are either black or white—with no yellow coloring.
In contrast, the birds in the first two photos have a dull “masking” on the face (eyeline and auriculars), a crown of similar dullness, and a nape and mantle area that is “greenish” yellow, similar in hue to the masking on the face.  Also note that there is a yellow wash on part of the breast, belly and vent areas.
With these and other identifying traits, the first two photos are of Black-throated Green Warblers!  The Black-throated Green is a spring and fall migrant through Texas, and frequent winter resident of the Rio Grande Valley.  BUT, you note, the first picture shows the black throat, and the second picture does not!  Thus is my interest in posting this blog. 
The first photo is a male Black-throated Green (BTG), with the clear markings, including black throat of the male.  The second photo appears to be a female BTG.  BUT, why would I find a male and female BTG in the Austin, Texas area mid-May?  My multiple website analysis confirmed that, like the Golden-cheeked Warbler, the male and female BTG Warblers migrate separately, with males arriving in the Canadian and Northeastern U.S. breeding grounds first, and females soon following.  But breeding season is categorized as April to Mid-May, and these photos were taken mid-May while hiking a section of the Balcones Preserve in Austin, Texas.
So, my subjective best guess, based on very little objective evidence other than the first two photos above and an afternoon of web “research”, leads me to believe that either: 
1) The photos are of a mature male and immature male (that does not yet have full throat coloring) BTG Warbler; and that these two are somewhat late or off-course migrants; or
2) The photos are of a male and female BTG Warbler that seem to be “breaking the rules” of migrant behavior and location.
So for those reading this blog that are not (yet) birders, you have added the ability to distinguish between THE Native Texan (the Golden-cheeked Warbler) and the Black-throated Green Warbler, a beautiful “good get” spring migrant.
And for those reading this blog that are birders, what say you--first year male or mature female?  Thoughts on migration or other suggestion? 

I’ll look forward to your comments.

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