Looking for help on visual differences between a few species (1 Viewer)

I've been compiling information on hummingbirds recently as a few of you may know. There are many species that I will eventually be illustrating, but there are lots of similar birds which I can't find visual differences in.

Basically I'll post some species pairs that I can't find information on separating. If you could point me towards ID traits that are different in the two species, I'd appreciate it immensely. Many species are vastly different in geographic location so the differences are rarely if ever noted in literature it seems.

This thread will be continuously updated with new queries as time goes on.

List:
1. differences between Green-fronted Hummingbird Amazilia viridifrons vs Chestnut-sided Hummingbird Amazilia (viridifrons) wagneri

2. differences between Canivet's emerald (Chlorostilbon canivetii) and Cozumel emerald (Chlorostilbon forficatus). (regarding Canivet's male vs Cozumel male and Canivet's female vs Cozumel female). Actually anything that shows all emeralds, male and females, would be awesome, but I doubt something like that exists. Would be too good to be true...

Don't know if this forum has a character limit on first post but reserving a second post just in case. No yelling please

I assume you've read the sources, but if not:

(1) Rev. Soc. Mex. Hist. Nat. 25 (1966): 222.

(2) Proc. Biol. Soc. Washington 3 (1885): 23.

Good luck--