White River Ivory-bills at carrying capacity?

Here's an intriguing quote from an August New York Times article (the bold font is mine):

In a telephone interview today, Bobby Harrison of Huntsville, Ala., one of the first people to see the ivory bill in the Cache River, said he was never worried about the criticism. He added that he figured that the bird had come north to the Cache River only because there was no room in the White River refuge. "It's already got ivory bills in it," he said.