I live in southern California, so we can see hummingbirds any day of the year. Sometimes hummer interest on this forum seems to start and stop with the ruby-throated, or the occasional vagrant from the west, so I don't bother posting much. You seem to be a keen observer of hummingbird behavior, as am I. Sometimes I study the individual residents and chart out their various territories in my garden. Many have their favorite flower species and personality quirks. Most are Allen's or Anna's here, but rufous often pass through during migration. Several other migrants are also possible.

While the species are different, some of the behaviors may be shared. I know that when certain favorite flowers in nearby locations are in bloom, fewer resident hummers may appear in my garden during that time. Another reason for fewer visits to feeders in May and June in your area may also be the availability of other food sources. Then in August, when the nearby nectar sources are drying up in the summer heat, they may frequent feeders in greater numbers.

Thanks for this information, gyr-falcon. I hadn't really thought about it that way, but you're right, August does turn dry and flowers are much scarcer. In fact, most years August is just plain tired and ugly.

I've been thinking only in terms of numbers of hungry mouths, but availability of food is another variable, and just as important if not more so.

Thanks again, I see just a little clearer now.