I was hearing all these broad-tailed hummingbirds (Selasphorus platycercus) flying around near Echo Lake and it seemed impossible. What was blooming for them to eat? Willows. They were buzzing about the willow catkins at 3200 meters (10,500 feet). This male was bold enough that he moved to within one meter of me and my friend. Nice experience. First time in a more wild setting to get to observe a humming bird up close.
It is still quite early spring up there on the 3rd of June and almost nothing else is blooming at that altitude.