I'm sure the bird was planning to mount an attack and was only thwarted by Oscar's intense scrutiny. We have geese that Emma has to keep a close eye on too!
In general, birds are extremely dangerous. It may get used to you if you will feed her. Just if your windowsill will have many birds, then you may have raccoons. Raccoons look harmless, but they're dangerous. I have tested this on my experience. I often fed the birds that came and could spend the whole day under my windows. Everything was fine until the raccoons started sneaking into my yard and catching birds. At first, they were just hunting for birds, but soon they were trying to get into my house. I was scared when one of the raccoons managed to get into my house and hurt my dog. I immediately turned to experts that work with wild animals, and they caught all the raccoons. These creatures caused a serious injury to my dog, it took a month to heal all the wounds.