The Silver Bird Vessel is the seventeenth treasure that can be found in Uncharted: Drake's Fortune.
The Silver Bird Vessel is found in Chapter 4 - Plane-wrecked. This treasure is very easy to miss. It is separated from the previous treasure by a platforming section. Once you finish the platforming section and before you move onto the next area (containing numerous wooden death traps), head to the right and to the cliff. Be very careful here because you will fall off if you move too far from the edge because there is nothing for you to hang onto here.