Here in Southeast Alaska (SE AK), we have one species of hummingbird that is very common in the warmer months, the Rufous Hummingbird, Selasphorus rufus. These guys show up in the Wrangell area in the early spring, the very early spring before there are any flowers blooming or leaves budding out and not even very many insects out and about yet. Many years there is still quite a bit of snow down to the lower elevations as well so I was always interested to know how they were able to consume enough calories to meet their incredible daily energy needs. It was a mystery for me until about 10 years ago in early April when I was walking a very popular trail here in Wrangell and had stopped to watch a Red Breasted Sapsucker, Sphyrapicus ruber, working a group of willows. Sapsuckers are a type of woodpecker that specialize in drilling holes in trees in order to feed on the cambium and sap. When the sapsucker flew off to another group of willows, a hummingbird immediately fly in to the newly drilled holes and fed on the sap! Mystery solved! A few days later, I saw the same sequence of events in a different part of town in a different group of willows. I have since watched Ruby Crowned Kinglets doing the same thing in the winter.
This is a photo of sapsucker holes on the trunk of a dead willow. The holes have effectively girdled the tree and are quite possibly the cause of its demise. I find the relationship between the sapsuckers and hummingbirds really interesting and am now curious to know if a hummingbird follows the same sapsuckers throughout the spring until there are enough flowers blooming or feeders out on porches to allow them to go their own way.