There are so many reasons why cats love trees so much and now that spring has come, they just start flying up. And no, they have never heard of Bird's rights.
One interesting fact about cats and trees id that If you look closely at your cat's claws, you'll notice that they are curved in a downwards direction. That is the reason they can easily scale trees. But when a cat wants to dismount from a tree, they have to sort of scurry down backwards. This is due to the curve of the claws, which prevents them from climbing back down the tree face first.
Anyway, these cats seem quite satisfied up there and not too concerned with how they will go down.