The timing of the disaster had especially worried scientists and bird-watchers, since it came amid the annual spring migration of tens of millions of birds through the Gulf of Mexico.

(Watch video: "Gulf Spill Still Threatens Millions of Migrating Birds.")

"There is still the potential for impacts, but nothing like last year," said Michael Carloss of the Louisiana Department of Wildlife & Fisheries.

Carloss, who directed the agency's rescue response, hasn't seen any "obvious" changes in migratory patterns or the numbers of birds arriving or passing through Louisiana—a major bird habitat.

But he describes the damage assessment to wildlife as a "long,