Birds fight over territory, potential mates, and food. 

In the photo set below Kelly Munday illustrates graphically the steps in the Bald Eagle attack on a Trumpeter Swan in British Columbia on a lake. She describes the photo opportunity as follows: 

• "My husband, son and I were out in our boat on Lakelse Lake in Terrace.  We were at the mouth of the Lakelse River where I spotted a pair of Trumpeter Swans and started photographing them.  The pair split up and one swan flew past me and a Bald Eagle came out of nowhere, grabbed the swan, struggled with it for approximately 5 seconds.  Feathers were flying everywhere!  The swan was quite a bit larger than the Bald Eagle and the swan broke free, dropped and then flew back to the water.  We waited to see if the swan was okay and it appeared to be fine, just a few feathers lost.  I have never witnessed this before and none of the ornithologists that I have talked to have ever witnessed this before.  The swan was approximately 100 feet over me and I was in a moving boat so the pictures aren't as clear as I would have expected with this lens but needless to say an absolute amazing series was captured!"