I'll preface all this by saying I'm no expert, but I think I can give you a tip or two that helps me.
Birds in flight are crazy hard. You can't just reach up and move the sun where you'd like it to be to light the bird. The bird very seldom takes flight in the direction you'd like, and it's always hard to get close enough. Often, you have only a second or two to react to a bird taking flight or appearing overhead. It's a really fun challenge!
I would use a faster shutter speed if I were you. I typically use at least 1/1000 and prefer 1/2000. Birds move quickly, especially the wing tips, so I like to shoot a really fast shutter speed to stop the motion. I try to approach birds with the sun at my back, but terrain doesn't always permit this. Also, so many BIF shots are opportunistic, just being in the right place at the right time.
Your shots are pretty good, and I think that with some post processing to bring out the shadow details, they could look even better.
Keep shooting and posting!