I can state that because this one doesn’t infect migratory birds which don’t die from it but do fly around the world infecting humans wherever they go.
Hell even if it did, the bird population is a fraction of what it was in 1918.
In 1918 you could not have functional national quarantines because of all the passenger pidgeons. That is why Passenger Pigeons are extinct today - they were intentionally eradicated in the twenties.
They used to teach this in school, and when I was growing up I was interested in the topic and read a lot of books about the times. And of course the men who fought in the Great War were only in their sixties then and I loved to hang out with my grandfather at the barber shop or the grain elevators and tractor stores and listen to those guys reminisce.
Passenger pigeons were extinct by 1914. Not sure where you are getting this.