Certain birds can share the same tree as a 'food source' by looking at it from a different perspective. The Downy Woodpecker and Brown Creeper, for instance, will hunt for insects while going UP a tree. Conversely a Nuthatch will hunt for insects on the same tree(s) while going DOWN.
Check out this Screech Owl video;
What is the magnitude of the oil spill in the Gulf? (Not just the beaches but the whole Gulf)? For a comparison, the Exxon Valdez oil spill in Alaska in 1989 was 11-million gallons. It's estimated to have killed between 100,000 and 250,000 seabirds.
The recent Deepwater Horizon spill ("leak" actually) let about 210-million gallons of oil pour into the Gulf. Dead birds are still being counted, and more deaths will occur for decades; the bird deaths may total well over a million.