This rather lengthy statement is the result of a couple of discussions with people who wanted more explanation of the TBRCs stance on Allen's Hummingbird records and what birds are eligible for consideration.The undisputed identification of an Allen's Hummingbird requires precise measurement of the outermost tail feather/retrix (R5) and examination of one of the interior feathers (R2). The identification of adult male Allen's Hummingbird without these precise measurements is a controversial topic. In August 2001 the Texas Bird Records Committee (TBRC) made the decision that some Allen's Hummingbirds would be considered for state records without these measurements. The caveat is that this group would only include fully adult males. Fully adult means males that are after hatch year (AHY) with fully developed gorgets and adult retrices. First-winter male Allen's Hummingbird molt into this plumage during the late winter/early spring (depending on how you define these periods) and are often in fully adult plumage by mid-February. These first-winter birds can have some residual rufous tipping to the upper back feathers causing the back to look dull. Birds with this plumage characteristic require tail measurements to confirm the identification. In order for the TBRC to be able to accept records of AHY male Allen's Hummingbirds without in-hand measurements, good quality photographs that show the tail, throat and back are required. So what does this really mean when there is a Selasphorus hummingbird visiting your feeder and you are trying to decide if it is possibly an Allen's? Some of this discussion may seem overly detailed, but I want to be very clear.
First of all, and very importantly, ALL female and immature male Selasphorus hummingbirds have green backs. This includes individuals of three species in the United States (Broad-tailed, Rufous, and Allen's). So all birds in these groups must be eliminated, as only in-hand examination of the tail can separate Rufous from Allen's Hummingbirds. That only leaves one category, fully adult (AHY) males with the aforementioned fully developed gorgets and adult retrices. A fully developed gorget refers to a bird that has the brightly colored throat with the "corners" that extend down the throat. Adult retrices lack the white tips seen in immature males and are rufous with a black marking on the tip. For the TBRC to consider a potential Allen's Hummingbird as a state record without tail measurements it has to be a "textbook" AHY male. This link shows such a bird:
Close (and extended) examination of a potential Allen's Hummingbird are required to make certain that the bird does not have patches of rufous/brown feathering in the back. Any brown feathering in the back eliminates Allen's Hummingbird from consideration without tail measurements. An adult male Allen's is slightly smaller than a Rufous overall. The green on the back covers the central back and some rufous color may extend just above the folded wing. The rump will be rufous and it will extend well up on the lower back. In general, the rufous color present on the face, sides, flanks, rump, and tail tends to be more chestnut brown than the orange-brown color of Rufous Hummingbirds. The tail generally appears shorter and much more pointed than that of an adult male Rufous when the bird is at rest. As a general rule, Allen's Hummingbirds are much less pugnacious that are Rufous Hummingbirds.
The controversy stems from whether fully green-backed adult male Rufous Hummingbirds exist and how frequent are they in the overall population. The short answer is yes they do/can exist. McKenzie and Robbins (1999) made an extensive survey of specimens of AHY male Rufous and Allen's Hummingbirds and discovered two undisputed green-backed AHY Rufous Hummingbirds (95-100% green feathering) and three others that may be hybrids, including the specimen that had often been cited as evidence of the existence of green-backed AHY male Rufous Hummingbirds. As a result, there is appropriate concern that such individuals would be lumped in with true Allen's Hummingbirds if they are not captured and measured. Many purists contend that these measurements are essential to the acceptance of any Allen's Hummingbird and I certainly respect their opinions in this matter. Having said that, I have a different opinion which I (of course) think is supportable.
Here are some facts that weigh heavily in my consideration of this issue. There have been 22 Allen's Hummingbirds documented in Texas since 1 January 2002. Most of these (17) were captured by banders and tail measurements accompany the documentation. The range in dates of occurrence are from 13 August-28 February. During this time, these same banders have not captured a single fully adult AHY male Rufous Hummingbird with a totally green back despite capturing approximately seven times as many Rufous Hummingbirds. Brent Ortego, the most prolific hummingbird bander in Texas, stated in a note on TexBirds on 1 August 2002 - "I have handled hundreds of Selasphorus in TX with roughly half being male. No male was fully green-backed when it approached maturity. On the other hand, our banding team has handled at least a dozen Allen's in TX with most being male. I have only observed one adult male Rufous out of thousands with a partial green back in my travels. A fully green-backed one would be very rare." They have banded many more than that dozen Allen's Hummingbirds now.
To add to the overall picture, let us also consider Allen's documented in Louisiana. There have been 42 Allen's Hummingbirds banded in Louisiana since the fall of 2001. Therefore at least 64 individuals were documented between these two states in roughly the last two and a half years. You can imagine how many more were present. This sets the foundation that Allen's Hummingbirds are a regular migrant and winter visitor to Texas. It is my contention that an AHY male Rufous Hummingbird with a totally green back is an anomaly in nature and is very, very unlikely to be encountered. Is it impossible? Clearly "no" is the answer to that question, but equally importantly, should the TBRC ignore the preponderance of data to eliminate the possibility of accepting a Rufous Hummingbird as an Allen's? I think "no" is also the answer to that question. In my opinion, the chances of doing even that are remote. From everything I have read and heard the percentage of fully green-backed males in the overall population of AHY male Rufous Hummingbirds has to be well below 1%. It certainly does not appear to be a scientifically significant percentage.
McKenzie, P. M. and M. B. Robbins. 1999. Identification of adult male Rufous and Allen's hummingbirds, with specific comments on dorsal coloration. Western Birds 30:86-93.
Secretary, Texas Bird Records Committee, April 2004