Primary Identification
The first thing to look for when identifying a White Ibis is the curved pink bill. This unique feature immediately sets it apart from other all-white birds like the Cattle Egret and Great Egret.
While not as immediately apparent, the White Ibis does present with black tips on the (click the image to see a larger version where these tips are just barely visible) that are very clear during the birds flight.
Juvenile Form
The juvenile form of the White Ibis still possesses the distinct curved bill, but instead of being all white, it will instead be a mottled brown and gray. The presence of adults in the area, combined with the curved bill, can be a helpful indication that you are seeing a White Ibis.