 The use of standard blue screen techniques for doing matte shots of  the birds proved to be unacceptable. The rapid movement of the  birds, especially their wings, caused excessive blue fringing in the  shots. It was determined that the sodium vapor process could be used  to do the composites. The only studio in America that was equipped  for this process was the Walt Disney studio. Ub Iwerks (qv), who  had become the worlds leading expert on the sodium vapor process,  was assigned to this production.