Rufous vs Allen's?

Usually when you see a bird you cannot I.D. you just go to the species family section in a guide book or cellphone app and pick out the picture that looks like your bird. Sometimes not. A photo really helps. Sometimes.

Gunnar to Rick Snider: 

"Is this an immature male Rufous Hummingbird ... or female?" (versus an Allen's?)

Rick:

"To identify as a Rufous you have to have a clear spread-tail shot to see if there is a narrowing of the tip of R2 which the Allen's doesn't have. Often males have more rufous on their top tail feather, R1, females less. Spots in the throat are variable. Only adult males can be be identified as Rufous, rather than Allen's, if they have a substantially rufous back."

Gunnar: 

"I did get a rather poor photo of the Allen's at Justin LeClaire's backyard earlier in the week. Couldn't prove it by me, but Justin and the Delesantros did I.D. it."

Rick: 

"Yes, green in the center of the back of an adult male means Allen's in almost all cases. A small number of green backed males, percentage not well established at 2% in California, are green backed Rufous in which case they have to measure the width of R5 in the hand to prove it is an Allen's and not a green backed Rufous. In Justin's case with two green backed males one was banded and R5 measured to remove all doubt. The second male was not captured and measured so you have to go with the fact that 98% (or whatever) of the green backed ones are Allen's and call it an Allen's.

 Slightly less confused - Gunnar