This is an article on an analysis that found that children raised in greener areas have higher IQs AND lowers levels of difficult behavior - and this is on humans who are the ultimate domesticated animal so consider how important it is for your bird's wellbeing (emotional, physical AND cognitive) to have an environment that resembles the wild: natural light from a nearby window, a solar schedule, flight, large cages, a big bowl of water (make sure it's not too deep), natural branches (with leaves if at all possible), toys made out of natural elements as well as 'earthy' colors surrounding them - and don't be afraid to use things like grass, soil, rocks and edible plants. It all adds up!
https://www.msn.com/en-us/news/technolo ... li=BBnbcA1
And some more:
https://www.interiordesignology.com/how ... ell-being/
http://naturalhealthperspective.com/fea ... ealth.html
https://www.ecowatch.com/study-shows-li ... 58780.html