Hummingbirds

I'm pleased to say that my hummingbird feeder is proving a hit - getting lots of use.  I need to get some photos, but these birds are very skittish so that might prove tricky.  But when I'm on my sofa and glance outside, nothing beats the view of a hummingbird hovering by the feeder and feasting on my homemade sugar water (1 cup sugar, 4 cups water, mixed together).  I think they're territorial, so I guess it's mainly just the one bird making use of the feeder - but occasional I see a pair, or a bird that looks to be a slightly different color (they're kind of all grey/green, so quite difficult to tell).  I'm also not entirely sure whether they are migratory - particularly in the Pacific NW.  The internet tells me that there is one type of hummingbird that will stay year-round, but I don't have a clue if that is what I'm seeing - generally, I am utterly clueless when it comes to identifying any sort of birdlife in the US.