Authorities immediately restricted access within a radius of three kilometres of where the bird was found as tests were under way to see if it carried the highly pathogenic strain which can kill humans.
Tough new measures come into force in infected areas in five states on Saturday, with cats having to remain indoors, dogs on a leash and access to poultry farms restricted to employees and veterinarians.
The H5N1 virus was first detected in mid-February in wild swans on the Baltic Sea island of Ruegen in Mecklenburg-West Pomerania and since spread to two other states in the north and two in the south, Bavaria and Baden-Wuerttemberg.
Earlier this week a cat on Ruegen died of bird flu in the first case of a mammal in Europe in which the lethal strain was positively identified.
Experts believe the animal might have died after eating an infected bird, following similar cases in Asia, where the disease surfaced in mid-2003, infecting 174 people worldwide, 94 of whom have died.
The spread of the disease in Germany has been blamed on migratory birds resting on their way from Asia.