Bird photography is a slippery slope heading towards a very frightened credit card
, and you have made a good start here Ade. We all have our own styles and techniques, but there are a few things to try when you first start, these are the basics for you to build your own style on.
There has been some good advice already offered, but with small birds like these, the closer you can get, or the longer focal length lens you can get the better.
I'm assuming looking at your settings that you were using your lens at the 250mm end, and with a shutter speed of 1/160 for all the shots. You have changed the aperture and ISO for the different shots. At 250mm, the rule of thumb is that you need a shutter speed equal to the focal length when hand holding. That means that at 250mm, you need a shutter speed of 1/250. The 70D is a 1.6 crop sensor, and so the 1/250 should be increased by 1.6 which is 1/400 or nearest above. The IS on the lens will allow you to reduce the speed by a stop or two, but it is preferential for fast moving birds to keep your speed higher.
In the case of the Greenfinch, you would have been better reducing your aperture by a stop and increasing your shutter speed by a stop. Having said that, the Greenfinch is the best shot you have posted.
My standard settings are either manual, or AV, I would suggest AV is the best for you to start with. For birds, generally keep your aperture wide, and if the light is poor, increase your ISO to give you the required shutter speed, then change the shutter speed for different lighting conditions rather than changing the aperture.
Evaluative metering is good for this genre, and use central AF point aimed at the eye. RAW is the best format in my opinion, but if your not conversant with it, I would suggest taking it a step at a time, get used to your shooting techniques first, then move on to RAW.
There's lots more but you do need a starting point and there's nothing to be gained by trying to run before you can walk.
I hope this helps