I greatly appreciate the information Cornell puts out on issues such as how frequently (in days) that hummingbird feeders need to be cleaned and replenished according to outside temperature. I'm wondering if there are any similar guidelines on how much to increase the water in their sugar water as the outside temperature heats up. For example, at what point would you want to increase the sugar water ratio to 5:1? I've been increasing the water content incrementally, as I figure conditions are different when the temperature is in the 90's than in the 100's, and then in the 110's and beyond, etc. However, I'm looking for a more authoritative and definitive guide on what the ratio should be in various temperature ranges.

If anyone here knows and/or has encountered such a guide, please let me know!