Allen's Hummingbird (Selasphorus sasin) vs. Rufous Hummingbird (Selasphorus rufus)
Most Rufous Hummingbirds have atleast some green flecks on their backs at some point of growing up. Some lose them by the time of adulthood. Some keep or gain more into a "green-backed" Rufous Hummingbird status.
It's this green-backed Rufous Hummingbird that is near identical to the adult Allen's Hummingbird, a bird that always has a green back.
Where ranges overlap, it can be difficult or impossible to separate the two other than having the bird in-the-hand. As time marches on, there are those who are learned enough in their bird observing, field-work and/or region they live in that can tell the difference between the two without it in-hand. Others atleast have experienced leanings toward one species ID or another. The advent of high-shutter speed digital photography has helped, too.
There was an effort today to capture two green-backed Selasphorus species hummingbird.
We caught one. One person in the party is long-timed permitted to do this.
Allen's Hummingbird , Marathon, Brewster Co., TX. A location where migration routes do overlap.
One way out of the hand to get a strong hunch is this:
Hatch-year (HY), birds hatched this calender year (have a mixed audience reading), Allen's Hummingbird male develop their full gorget earlier than do Rufous.
This HY male Allen's is well on his way.
By the way, HY hummingbirds have corrugations or wrinkles/grooves running alongside their bills. After-HY birds typically lack them completely or they are almost gone.
That's what Kelly is looking at in the above pic.
This HY bird (and us for that matter) is all the way into the month of December. It's lost some its older feathers, though has some left.
Check out the primary feathers of one of his wings:
It has new secondary feathers. It also has new primary feathers except for the outer-most 3 (P7-9). More brown in color and certainly more worn on the edges. He's growing up.
Also, his tail still has some old pin feathers amidst newer adult tailfeathers.
Moving from age-characteristics of humming birds back to species specific characteristics making this an Allen's Hummingbird, and not a green-backed Rufous Hummingbird...
These two species have 10 tail-feathers or retrices. There are five on the left and five on the right. The innermost are both labeled tailfeather number 1 (or R1). So from the innermost two tail-feathers, our R-1's, we count outward; R-2, R-3, R-4, R-5.
In the above photo, those two thickest feathers by his index finger are the R-1 tail-feathers.
R-2 feathers on a Rufous Hummingbird has a notch in it.
R-2 feathers on an Allen's does not.
No notch here.
All the tail-feathers in each sex and age-class are narrower in Allen's compared to Rufous.
This become more acutely apparent in R-5. The outermost tail feathers. They are narrower in Allen's Hummingbirds.
Again, no notch in R-2, and check out the narrower outermost tail-feathers. Somewhere we can dig up a photo of the tail of both species side-by-side. I'll edit that in, in the future, perhaps.
Anyways, as is standard procedure in avian fieldword various physical measures were taken.
This is wing chord length:
Chord length is a measurement taken when a bird's wing is bent at around a 90 degree angle (sort of as if it were at rest). The length from the "wrist" to the longest primary wing tip is taken.
Check out his new band on his right leg. Tiny.
I've worked with band sizes from albatross, sulids, shearwaters, noddies, terns, warblers, vireos, shrikes, and others. The band size for a hummingbird is amazing!
Measuring tail length:
Width of the outer tail feather:
After various other morphological data taken, this HY male Allen's Hummingbird with a healthy weight was released ... with a bad auto-focus..
Another far-West Texas Allen's Hummingbird. This is the latest calender date that Kelly has banded an Allen's. Kelly's been doing this for a long time.
**He later banded an Allen's Hummingbird this afternoon at a friend's place in Alpine.