Reportedly three Maltese Falcons were created for the film. Two of lead and one of lightweight resin.
Here is a link from Guernsey's Auctions which speaks about them:
The iconic falcon statuette at the center of John Huston's 1941 film-noir masterpiece "The Maltese Falcon" (Warner Bros.) is one of the most important and recognizable objects in the history of cinema. As the legacy of the film has continued to grow, more so has the intrigue surrounding the seductively mysterious falcon statuette.