ok so yam's parents being huge on animal rescue and they have a house full of animals. dogs, cats, rodents, birds, fish, reptiles, they've got em all. every day when the two of them get home from school they get mauled by three dogs, a macaw, five ferrets, two cats, a goose, a monitor lizard, and a pig before they can even take their shoes off - potion seller (bonus: yamaguchi carries around sugar gliders in his pockets always and the birds all flock to tsukki like he's a living playground)
To add onto the Tanked post, they also keep large birds in the building they build the tanks, near hazardous equipment and fumes that could potentially kill the birds. All in all; Birds don't belong there and it's a hazard to their health.