The 45-year-old defendant would reportedly gain access to ornithology collections at various museums in countries including Switzerland, Germany and Austria, claiming he was doing scientific research, according to the ATS news agency.
He would then pluck feathers off exotic and valuable birds, stealing what were described as "very rare and precious objects, of inestimable scientific value".
His victims included red kites and buzzards, a variety of eagles and the endangered Usambara eagle owl of Tanzania.
The man, whose name has not been released, has been charged with the theft of feathers from 127 different species over more than seven years.
According to state prosecutors, the losses suffered by the various museums amounted to six million Swiss francs (5.4 million euros, $6 million).
His trial is due to start on Tuesday and a verdict is expected the following day.