It's not necessarily a matter of not wanting to share space. Some birds instinctively build nests on cliffs, but when their instincts drive them to nest on the

It's not necessarily a matter of not wanting to share space. Some birds instinctively build nests on cliffs, but when their instincts drive them to nest on the side of skyscrapers, their young end up falling to their deaths since skyscrapers are taller and more vertical than the cliffs they evolved around. (Fledglings falling out of nests is normal, but in natural environments is rarely lethal.) In cases like this, anti-bird architecture is really just an attempt to say "no really, this isn't a good place for a nest".