A pewee at Packery Channel, Corpus Christ, TX, September 13 2015
Background: in early October 2011 one to three Western Wood-Pewees were identified on Mustang Island, located a few miles north of Packery Channel which is an area of live oaks and scrub in a small subdivison on the barrier island of (North) Padre Island. CLICK HERE to read about that event and see photos of the birds.
Eastern WP (EWP) is a common migrant throughout the Texas coast, breeding from the east Texas Pineywoods west through north-central Texas and throughout the Edwards Plateau in the center of the state. WWP is a summer resident in the higher mountains of west Texas, and a scarce migrant west of the Pecos River and in the western part of the Texas Panhandle. Despite breeding as far east as south-central Manitoba, WWP is extremely rarely-documented in central and eastern Texas - largely due to ID problems associated with the expected EWP.
In the early afternoon of September 13, 2015 Martin Reid (MR) found a WP with an extensively dark mandible* - in fact as dark as the darkest mandible he'd ever seen on WWP in their normal range. The bird was hunting from a low power line just above a line of small live oaks, as were a few Eastern Kingbirds and an Olive-sided Flycatcher, intermittently. MR obtained a series of photographs, but it remained silent and ignored playback of EWP and WWP vocalizations. NOTE: it was blustery, with a fairly strong north wind, such that all birds that were perched in the open were "leaning-in" a bit.
Early afternoon on a hot sunny day in south Texas leads to difficulties in lighting/dynamic range when photographing birds - especially when the bird is high-up and in the open and there is limited opportunity to change the angles relative to the high sun. Thus almost all the photos were taken at various levels of overexposure. All the tyrannids that were perching on the wires looked relatively paler above than when viewed in more neutral lighting.. I have included at the bottom a photo of an Olive-sided Flycatcher to offer a point of reference - but note that it was much further to the right and is from an angle that was not capured for the pewee.
* Pyle, in "ID Guide to N.A. Birds, Part 1" provides an illustration of WP mandible patterns from below (Figure 142 on page 215): they show decreasing amounts of distal duskiness from left to right across four examples. The text states that the 3 leftmost patterns exhibit the range for WWP and the 3 rightmost patterns exhibit the range for EWP. Put another way, the middle two patterns can be found in both species, but the leftmost pattern (which is more than 3/4 dusky) is outside the range of EWP, while the rightmost pattern (which is pale except for a very small dusky tip) is outside the range of WWP. As with all attempts to limit the range of a morphological feature, I expect that extremely rarely, an EWP could have duskiness approaching or matching the illustrated leftmost pattern in Pyle's Figure 142 - but keep in mind this is meant to show the darkest limit for WWP, so an EWP like this should, in theory, be quite exceptional. Looking at the pewee seen at Packery on this day, in all of the many photos at different angles the mandible is almost entirely dusky/blackish - even more so that the darkest pattern shown in Pyle's Figure 142.
There is an ID article for the two Wood-Pewees from the ABA's BIRDING Magazine (CLICK HERE to link to it). Reviewing the ID points discussed therein, I'd score the Packery bird thus:
1. Voice: N/A. 2. Contrast between upper and lower wing bars: Somewhat intermediate - but seemingly okay for Fall WWPs - see below. 3. Ratio of primary extension to tail extension (PE/TE): In one or two images, seems very close to 1:1, but in others it appears lightly less. Compare to this WWP from California in October. 4. Gestalt (tail angle): In all photos the wings and tail look to be in-line. It is possible that the windy conditions were affecting this to some degree, but the posture seems consistent across all situations. 5. Lower mandible coloration: All-dark. At most there was a very slight paling immediately next to the edge of the arc of feathers at the base. Note that in the linked-to article it says: "Some Easterns occasionally have dusky lower mandibles extending from the tip and halfway to the base of the bill, overlapping with Western's lower mandible. In addition, some Westerns can have almost entirely pale lower mandibles. We thus caution that this field mark alone is not reliable.". This implies that the extreme pattern for EWP is for the dark to extend "halfway to the base of the bill" - the mandible pattern on the Packery individual is significantly darker than this. 6. Overall coloration of underparts and upperparts: Hard to assess properly in the lighting conditions. NOTE: since all the photos are with a sky backdrop, all were over-exposed in order to gather detail on the underparts. The contrast on the underparts and extent of dark across the breast seem better for WWP.
NOTE: After looking at some photos of WWP on the internet, I noticed a slight difference in the covert edging between spring/summer, and fall. Here is a link to Brian Small's WWP photos from California; note that on the bottom three photos - from October - the wing coverts look fresher and the pale fringes to the median coverts are slightly more prominent than on the June birds. There also seems to be a tendency for the innermost median fringes to be slightly more prominent compared to the outer fringes.