He originally pleaded not guilty in May after being arrested in March. It's unclear why he changed his plea.
Dong is facing one count of illegally importing wildlife which carries with it a maximum penalty of 20 years in federal prison.
A second suspect has already pleaded not guilty to smuggling charges.
The trial of 34-year-old Duc Le is scheduled to begin next month.
He was arrested after investigators found 51 songbirds at his house.
AP contributed to this report.