There isn't one specific kind of bird that goes after drones the most. Birds of many varieties can be a threat, including:
Raptors (birds of prey) like eagles and hawks
Large birds like seagulls
Even smaller birds like crows and ravens
These birds might attack a drone for a couple of reasons:
They see it as a competitor in their territory
They mistake it for a predator trying to steal their food
If you're flying a drone, it's important to be aware of birds in the area and try to avoid bothering them. There are steps you can take to fly safely around birds, which you can find online.
Personally, I have never had hawks attack my drones. They often come circle around, but never stick around too long. Looks like they're just curious. Swallows often dive bomb close by, but never too close. The only birds I've ever had actually attack and chase my drone that I was worried about was a murder of crows, but I just put it in high speed mode and got away and landed quickly enough.
A tip, if you're in trouble with attacking birds, is to go straight up, which is hard for a bird to do quickly!
Also, there's another KZread video out there that recommends red reflective tape, which I have added to my drone. Haven't run into many birds yet, to test it, except for this one. I think it was a hawk, can't tell for sure!
Thanks for watching the video The ONLY birds I've ever had attack my drone were crows!