Isn't this counter to the idea that gaming can also slow cognitive decline for similar reasons?
The average CounterStrike player, for example, is scanning complex structures trying to identify an enemy, listening to sounds and trying to follow the source...etc. Why would the screen get in the way in one case but not the other?
Parent's point is IMHO that birdwatching involves a lot more attention, skill and experience than just plainly looking at a screen.
As sister comments point out, this could be reproduced with a lot more technology (VR with high precision controllers ?), which could bring it on par with playing Counter Strike in some ways perhaps ?
To expand on bird watching, people usually don't mindlessly choose a wood cabin and just sit there. They'll know which bird should be where depending on the season, where they tend to hide depending on the time of the day, their bird calls etc. and eventually trek to wherever the birds will be. It's also not so far from fishing.