I like that first shot a lot. You have an obvious subject, and a very non-distracting background. Good job capturing the catch-light in the eye. That catch-light is what gives this picture some “life.”
But to answer the question, whenever you want to do anything with a long lens with smaller aperture values, the first thing you need to think of is light. It looks to me as though you were shooting on a day when rain was threatening. Think: Dark sky, cool light, dead picture. You can fix some things in post-processing, but your best shots aren’t going to be the rainy-day ones. There is nothing that can replace strong sunlight for beautifying pictures. So do try to plan your shooting times (if you can) for times when the sun is out. Early morning is the best time for this; the sun’s light is ‘warmer’ and its angle will be lower.
I might recommend getting a slightly lower perspective, if you can. Putting yourself at eye-level with an animal subject, instead of shooting from above, gives a more personal, more interactive feel to the photo.
Just for fun, I played around with the first image in Darktable. Essentially, I saturated the image a bit more, increased the temperature in white balance, and made the whole image lighter. I also sharpened and de-noised it a bit.
But the main key with bird photography is Practice. You’ve got some great work here; keep it up.
Practice.
Practice.
Practice.
And have fun!
