A 2024 Natural England risk review [see attached] concluded that there is a very high likelihood that captive-reared mallards will be exposed to highly pathogenic avian influenza H5N1 after release. Once exposed, there is a very high likelihood of widespread morbidity and mortality in wild birds. The review concludes that captive-reared juvenile mallards have potential to act as both a reservoir and amplifier of H5N1 and to play a major role in H5N1’s continued persistence and dissemination.

The release of captive-reared mallards is already prohibited in Protection Zones, Surveillance Zone and Captive Bird Monitoring Controlled Zones. Releases are also prohibited in Avian Influenza Prevention Zones with housing measures.