The easiest way for me to tell is to look at the tail. I usually cannot get close enough without alerting the bird. Try this site, it is what I have used!

By the way, I last spotted a hummer on Sunday, was suprised to see a 'what I presumed to be' young male at my Red Nicotiana and Purple Petunias (can you believe it!) today. Must be a migrater, mine were almost all female this year, and knew how to use the feeders!! I guess all males must be taught........ :) Christy
Hope you find this usefull!

Here is a link that might be useful: rubythroat

thank you... i saw one this morning at almost day break... im in southern arkansas, the temps here in the mornings are around 40ish right now...