What kind of birds? Most of the birds I shoot are little guys jumping between a bush and a bird feeder about 3 feet away. I sit in my window about 30 feet away from the feeder with a Sigma 150-500mm lens on a tripod and a D5100 set for 1/4000 sec and lens wide open with ISO 3200. The shutter is set for continuous. Originally, I just pushed the button on the camera, but I just got a cable release. I first go out and set up a focusing target between the bush and the feeder and set the manual focus on the target. (The feeder is slightly forward of the bush so the flight path is at an angle to the camera. The depth of field of that lens at that distance on that camera is slightly less than 3 inches so I'm hoping to split the difference between focus on the feeder and focus on the bush.) Whenever I see any movement around the bush/feeder area, I fire a burst and hope for the best. In a couple of hours, I'll take about 400 or 500 pix and have nothing in about two thirds of them. Of the rest, most are thrown away due to being out of focus or just a partial bird either coming into the frame or going out of it. But there are a few that are rather interresting and OK focus (not really all that sharp, but close.) And then are one or two... I haven't had the opportunity to shoot large flying birds yet. I have shot birds feeding at the feeder. For those I was outside at a range of about 15 feet with the 150-500 lens. Focus was AF-S with apperture priority and ISO of 100 to 200. I set the lens so that the shutter is in the 1/200sec range. I just looked at some at rest bird pix and it seems I was using ISO 800 1/100 sec shutter and f6.3(wide open for the 150-500 set at 500mm) I used single point focus, mostly using the center sensor. The bird pix here were all from a tripod.