Six chickens have tested positive for bird flu after they died suddenly.
The discovery means a new 3km protection zone will be enforced in the Mont Felard area.
All poultry keepers are encouraged to house their birds to make sure they are kept separate from all other commercial, domestic and wild birds, though this isn't yet a legal requirement.
Other bird keepers outside the two exclusion zones are highly encouraged to house their birds too, as well as register their flock with the government.
Anyone with a flock of more than 30 birds is already legally required to register, but the States Deputy Chief Vet Caroline Terburgh says registering means bird keepers can be kept up to date 'on bird flu outbreaks and guidance on how to best look after your flock.'
Islanders are encouraged not to touch dead or sick birds but to report them by calling 441600.