Probably not blackbirds that you see, most like likely crows scavenging.

But anyway blackbirds are about the size of a robin, many of them have a red band on their wing. Blackbirds like to get into large flocks and swoop and dive together, especially the ones with no red band.

Most likely crows, which are a little bigger than a robin. Sometimes you will see several crows together, even working together.

Ravens are BIG birds, maybe the size of a small cat (less the tail length.) Ravens are more solitary.

Blackbirds like to live near the water. Crows do well in town around people, though they live in the country and do well around farms and ranches. Ravens like meadows and fields. At least the ones around here do.