Maybe another hummer, I've seen them chase others away for .25 miles...they can be very territorial.
I have a sliding glass door 5' from my feeder and never had a problem.
If you have cats in the neighborhood, my vote is on one of those worthless, evil, @#&*$%#@$%

Did both deaths happen during migration? I had one keep bumping into my upstairs window even though there was 5 feeders in my yard. He seemed to feel a feeder should be up there, high. Another flew right into my porch window. Both birds survived but were obiviously migrators. This never happens with my regulars. A cat probably would have taken it with. Also, in behalf of cats, the owner is to blame, not them. I've always had cats, inside. Safer for them and the birds.

I saw a picture on a hummingbird website of a praying mantis that was eating a hummingbird. It said they lay in wait near hummingbird feeders and stalk them, watching them come and go before making their move. If you see one on a feeder, chase it away. I googled hummingbird predators and found a surprising list that included spiders and their webs.

Regarding your hummingbird loss, I agree a cat would have taken the bird with him/her to either eat or show off to its master. I'd vote for the window accident. I had a hummer this fall keep trying to get at a hoya plant I have inside that is in bloom. It smells sickingly sweet. The bird just wouldn't leave the window alone! I finally had to move the plant away from the glass.

It would be hard for a cat to catch a hummer, they move to fast and aren't on the ground. My cats watch the hummers at the feeders (the feeders are up high) but don't really try to catch them. Cats mostly go after birds that are on the ground.

I hate to tattle on my dear puddy tat...when we lived in CA, (and I didn't actually have the understanding I have now about hummers, nor did I deliberately feed them... but she has caught MANY hummers in her past....NOW, thank goodness (and interestingly enough) when I put up feeders all over the place to draw them in, she doesn't even try to get them...In fact, she sits out on the patio under the furniture and watches them, just like me :)

There have been many times when they would fly down low to check her out...and she just watches stoically without any salivation :)

I wouldn't call cats evil or wothless, they are just following their instincts.....

And a dog tearing a cat apart is just following its instincts. Society doesn't tolerate pet dogs killing for sport and we shouldn't tolerate it in pet cats either (or either of them running feral). Because I love cats and birds I believe cats belong inside where they'll be safe and so will the birds.

I don't think it's cats because they wouldn't leave it laying there. I found another one dead on my front porch a few days after the last one. I think that they are fighting each other more than usual this year. I just don't know if it is the sugar water or what that is making them mean.

Ahhhhhhhhh Buford, but they do fly low. Mine were feeding off my Homestead Pink Creeping Verbena & also almost appear to touch the ground getting at some of the low agastache blossoms. I have also seen them chase anything that moves, including rabbits & ground squirrels, just inches above their heads.