Birds

I also think it is rare. It is hard for birds to see a window...it just looks like something they can fly through (until they crash into it).

Birds do not fly into cars on purpose. Usually it's a matter of the car and the bird reaching the same point at the same time. If the car is sitting still, then that is a different matter. It might be that they see reflections of the sky in the car windows and believe they can fly right through it. Same thing with house windows, especially large picture windows.

They are probably chasing insects and the car comes at them from seemingly nowhere to the bird in mid swoop.

Jeanne's answer is excellent. I would only add that, contrary to popular thought, many bird species are not highly or rapidly maneuverable in flight. (Exceptions include members of the nightjar [swifts, nighthawks, swallows], falcon [accipiters], hummingbird, warbler, vireo and sparrow families.)Couple that with the fact that very few things that birds encounter in their everyday world, including other birds, move as fast as an automobile going 55-80 mph. This makes it very difficult for them to gauge what a safe spacial buffer might be while flying. So, as Jeanne replied, it's not that birds intentionally fly into moving vehicles...it's just that they sometimes can't get out of the way fast enough when their paths cross.

Maybe they underestimated the car's speed or they dont care hit by cars because they can never be hit even by a running cars, too many amazing things I see from them at my rooftop before but it feels like they were pests with a bunch of them so I hve them bird spike and they never been back. Somehow I miss them.