The city is literally TEEMING with blackbirds, and these poor animals have to be caged.
Ravens are not city birds - this is not rooks who nest in and around cities - ravens live in forested and mountainous areas (i live in a bigger forest complex and there are a lot of ravens here but no rooks or crows (crows also prefer urbanized areas and they have a liking for river valleys) - consequently you cannot keep ravens free in a zoo park in the middle of the city - they are way too shy (while ravens are very intelligent and learn quick especially when young they become very novelty-shy while growing older)
blackbirds are known for their adaptibility to urbanized conditions they fare very well in city parks (if only is there places they can build their nests - a pair of blackbirds made a nest in a high ornamental shrub in the middle of our quite busy common yard - they are not shy birds)
blackbirds are known for their adaptibility to urbanized conditions they fare very well in city parks (if only is there p
by the way it's possible that what you call blackbirds are actually rooks (gawrony) - European blackbird