Wild birds are indeed the main way that avian influenza spreads, however `ars` is just grinding some axe of theirs. California does not have a free-range chicken regulation. Virtually all commercial chicken flocks in California are already housed indoors. The California "cage-free" regulation only enforces minimal standards against cruelty. It essentially codifies these industry guidelines: https://uepcertified.com/wp-content/uploads/2021/08/CF-UEP-G...
"Avian flu experts have called for caution in implementing cage-free requirements, noting that poultry exposed to the outdoors have a higher risk of contracting the virus."
"Incorporating lasers that deter wild bird populations into biosecurity protocols can help prevent the spread of highly pathogenic avian influenza (HPAI) between commercial poultry farms."
> Why is it only American free-range egg farms are being affected, while Canada and Mexico’s are being spared?
Mexico immunizes their birds, which is highly labor intensive, which they can afford due to low wages and the US can't.
Canada is far north and the infected wild birds have not gone that far in large numbers (although the numbers are increasing).
Immunization isn't just about cost. Many countries have decided meat from vaccinated chickens are not safe to eat and the US exports a lot of chicken to those countries. We cannot vaccinate until the others will allow it.
Source? Why is it only American free-range egg farms are being affected, while Canada and Mexico’s are being spared?