Originally Posted by StarlingWings
The sun makes budgies more active just in general--it is instinctive, but it's also physical. They absorb the UV and Vitamin D very well and it stimulates their activity levels
Also, since budgies see UV light, it urge them to be more active.
I think that's what it is, I've heard people ask that before
I was lead to believe that unless they are out in the sun, the Vitamin D doesn't get absorbed. Having it shine through the window isn't the same.
But I'm not 100% on this. I'm sure someone will know for certain.