2004 Update: The Costa's Returned! We first saw a male Costa's in our yard on April 25, 2004. It was scarce for a week and often chased by Rufous males, but as of May 3 it claimed the yard as its territory. This year, it remained through July 1.
A male COSTA'S HUMMINGBIRD visited our yard for five weeks in 2003 (first noticed June 5; last seen July 13). He seemed to like our yard, and was very territorial. In these pictures, he is perched on a low interior fence where he often sallied out for insects in the evening. At other times, he chose the top of a tall tree from which to survey the yard and keep intruding hummingbirds out. It worked for quite a while. On his first day here, all three of our regular hummer species (Anna's, Rufous, Calliope) were present. Within a week, only a female Calliope was able to stay long enough to be identified. In early July, we experienced an influx of Rufous Hummingbirds (including adult males). Costco (my dad saw the bird first, and proudly gave it this nickname) had to share the yard at that point, but lingered for over a week.
We often heard his scratchy, somewhat Anna's-like song, and he occasionally performed the Costa's characteristic dive display. Far from being shy, he stayed right on the fence when we were out working in the yard, and allowed approaches as close as 2 feet. After we watered the flower border, he sometimes drank water droplets left on the leaves.
Note: On the evening of June 6, 2003, I saw a female hummingbird at our feeder that I suspected was either Costa's or Black-chinned, but I saw it too briefly to get a positive ID. Unfortunately, it has not returned.