Bird ID please.

Please excuse 'feeder pose' and poor background. These little guys are a bit elusive, especially since the Pine Grosbeaks continually battle with them and chase them away.

Photo is from earlier today, north-west Wyoming. Doesn't show up so well in this image, but those wing markings are bright yellow. Closest I can find, in my Field Guide, is Brewer's Sparrow - but not an exact match. For scale, the feeder opening is about 2 inches wide, and 1-1/2 inches high, overall.

Thanks for any help.

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G'Jim c):{- ... 2x 50D (Both Gripped), 2x 7D (Both Gripped), 2x 5D Mk II (One gripped), 1x 60D, assorted glass (10-800mm), sundry accoutrements.
The beginner clicks the shutter and says "Let's see what I got." ... The experienced photographer thinks "How can I capture what I see?"
My Photography: http://www.gjimphotogr​aphy.com

you're a great friend, but if Zombies chase us, I am tripping you.

G'Jim c):{- ... 2x 50D (Both Gripped), 2x 7D (Both Gripped), 2x 5D Mk II (One gripped), 1x 60D, assorted glass (10-800mm), sundry accoutrements.
The beginner clicks the shutter and says "Let's see what I got." ... The experienced photographer thinks "How can I capture what I see?"
My Photography: http://www.gjimphotogr​aphy.com