The birds, comprising nine males and 12 females, were transferred under a conservation partnership linking captive breeding with efforts to restore endangered wildlife populations in their natural habitats.
The crested argus (Rheinardia ocellata) is an endangered bird species listed under Appendix I of the Convention on International Trade in Endangered Species (CITES) and Vietnam's Group IB of protected wildlife.
Saigon Zoo has spent years researching, breeding and caring for the species. As of October 26, its captive population stood at 44 birds, providing a foundation for conservation efforts beyond the zoo.
The 21 birds will be cared for and monitored at Bach Ma National Park, where researchers will assess their adaptation and breeding potential in the new environment.
The longer-term goal is to release future generations into the wild at Bach Ma, which was once part of the species' natural range.
The zoo and national park coordinated preparations and transport arrangements to ensure the birds' safety.
Saigon Zoo completed the required legal and quarantine procedures and assigned staff to monitor the birds throughout their journey by road to Hue City.
The partnership forms part of broader efforts to connect captive breeding programmes with conservation in natural habitats.
Saigon Zoo is also pursuing a similar approach for the Eld's deer, another rare species, to strengthen biodiversity conservation.