My macbook has a high cpu usage because of one process and i don't know why.
com.apple.bkagentservice is part of BookKit, which itself is part of iBooks.
Based on the limited information in your question I'd guess the BKAgentService is trying to reconcile your books in iBooks.app on your Macbook with the books registered against your account in iCloud, and some conflict is causing it to go a little mental.
Something I'd try is closing iBooks, killing the BKAgentService, then renaming the following two folders and re-opening iBooks. This will relaunch BKAgentService and it should start to sync your library from scratch.
That looks to me like a problem with iCloud. (com.apple.bird is a process of iCloud.) Try logging out of iCloud and see if that helps. If it helps, try logging back in and see if that breaks it.
I had the exact same problem, but a simple restart fixed it.