Flying Female Broadtail
This pretty hummer is probably a female, or an immature male broadtailed hummingbird (Selasphorus platycercus)
The first hummingbird at our feeders arrived on April 22, 2012. At first it was just a trickle -- just one or two a day. Now we have them dive-bombing each other and fighting over the feeders (we hang 9 quart-sized feeders around our covered deck and in the nearby aspen trees.) By mid-summer, the hummers will be draining all of them every other day.