I realize this may be a silly statement purely because it's so obvious, but here you go: feathers are very important to birds. Damage to the feathers can be harmful to the bird, very possibly leading to death. Now, when someone goes out of their way to harm a bird's feathers with, say, pink paint...that's shameful. And when that person gets caught...well, you can form your own opinion: Farmer convicted over painted hawk.
As an FYI, the bird species being talked about in this article is the New Zealand Harrier. More information on this beautiful bird can be found here.