Something a bit different for you today. I have enjoyed painting these head studies. I worked hard to maintain loose brushwork.
If bits started to get muddy or over-fussed, I wiped the area off and started again. I like working on board for that reason - it makes starting again much easier.
I used a No 4 flat bristle for the entire thing apart from the eyes, those little line thingies on the beaks and my signature. This is way bigger than I normally use for detail e.g. the tongue of the right-hand bird.
For that, I just used the corner of the brush and blobbed paint on, pointillist style, of the right colour and value until it looked right.
The other technique I tried, to achieve the illusion of feathers, was to wait for the paint to semi-tack up and then drag the brush at an angle and - well - feathered it.