I should have noted in my initial post that the bird guarding the feeder is a female Ruby throated bird. The other plain birds trying to get to the feeder are most likely either other females or immature birds. the only exception is the black throated bird.

We have seen no males this year at all.

Your hummer with the black markings is most likely a juvenile male ruby-throated. The 2 photos below, taken just seconds apart, show how the gorget feathers flash red when the light hits them just right. The feathers are dark, and refract light much like a prism or rain droplets.

I agree that you're likely seeing a young male Ruby-throated. Black-chinneds are possible in Florida in the winter but they typically don't arrive until late October or later. The gorget feathers of adult males and young male Ruby-throateds will often look black in poor/backlit lighting. You pretty much will need to see some purple feathers in the gorget of the Black-chinned to id one in the field.

I've got a list of all of the species that have been reported in Florida as well as some photos on the species page at floridahummingbirds.net.

Steve in Valrico

Here is a link that might be useful: Floridahummingbirds Forum