I talked to a farmer yesterday who said (at least in the US) it is bird flu. For some reason, the layers seem to have been hit harder than the boilers.
When bird flu shows up in an area, the only way to stop it is to cull the entire flock. Broiler chickens go from hatch -> slaughter in as little as 8 or 9 weeks. Hens need closer to 5 months before they start laying eggs. It just takes longer for the stores of hens to be replenished.
I was just in Vegas and the Flamingo didn't even have their birds out in display because of avian flu. The different bird species (including flamingos, natch) are all quarantined from each other somewhere else.