Thermals

I have an RC thermal soarer. I also have a few park-flyers that I fly in my cul-de-sac. Observationally, I think the classic explanation for thermals may be under-representing the contribution of evaporation. Wikipedia Thermals or What do Thermals Look Like?

Air with a higher water vapor content has a lower pressure than dry air. Therefore as water evaporates, the air mass is going to have a lower pressure and therefore tend to rise.

Observationally, the best thermal activity seems not to be at the time of day corresponding to the highest radiant heat (early-mid-afternoon), but earlier when evaporation from morning dew or a rainstorm seems highest. Similarly, in times of high humidity, thermal activity seems much lower.

Combining this with the idea that birds can see into the ultraviolet, I wonder if birds can actually see water vapor gradients and therefore detect thermals? Ultraviolet Vision in Birds: What is its function?