Economy

Concentration helps spread alright, but any exposure to an infected... hang on we've just had a pandemic. You know this stuff.

Wild birds are infected and dying all the time. They are the reservoir through which the infection spreads. Chickens are too controlled and, as you said, quick to die, to be good vectors.

https://opendata.agriculture.gov.ie/dataset/h5n1-wild-bird-species-identification