90% of the time they are swallows. Swallows do not attack your drone, they just fly around it in search of insects. The insects near any drone flee and therefore there are more insects around your drone per m3 than would otherwise be. Birds are much "wiser" than we humans will admit, especially when it comes to food. I've never heard of a collision between a drone and a swallow!
Seagulls will circle your drone flying above. Best to try and get above them and make them think you are the predator. They can be a pain during nesting season. Crows have an established home territory where they build nests and raise their young. Urban territories are about 10 acres, but rural territories are much larger. Crows hold their territories year-round. They will attack without question doing a barrel roll at your drone.
Hawks and eagles will take down your drone and its happened many times to even large UAV's like the Yuneec Typhoon H.