Another 70-300 user. Great!
The shots of that series were initially posted here
Red-winged Blackbird
This was a small marshy pond with lots of water growth and tall weeds. Normally they will either go up high on trees or light poles but in the ponds they will feel it is safer on top of the tall weed because they have an unobstructed view of everything around them.
Both the male and female were flitting from weed to weed but stopping for a while to scold me for pointing the camera at them. Once I knew where they most frequently landed, got closer and waited.
As long as our movement is slow and gentle they do not seem to be that easily scared off. Being used to seeing humans also helps I suppose.
Sorry if this is not much help but guess luck has also a great part to play in photographing birds of any kind.