I work with bird dogs (duck dogs and upland flushing retrievers) on a daily basis. Typically these dogs are Chesapeake Retreivers, Labradors, Golden Retrievers and Springer Spaniels. There are a few other breeds that I've worked with successfully but I can say I've never trained a Great Dane for bird hunting.
While a Great Dane still has a better sense of smell than a human they're more of a sight hound/sight hunter. Add that to the fact that most Great Danes in America have been watered down so much with breeding for looks and "gentle" temperaments that they won't hunt anymore anyway.
If you've got Great Danes, congratulations, you've got yourself a pair of nice house dogs. If you want a bird dog go get yourself a dog that was bred for it.
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