Ive seen vidoes on youtube showing birds and bats flying in slow motion at a nearly strict side view. Go look for them and pause the video at certain points and use as reference. Or go to spriters-resource.com/ and look up some bird/ bat sprites to use for reference. Another thing you could do is have him move up a pixel or 2 when his wings go down showing that hes getting some air lift from the flap.
You can also increase your contrast to make him pop out a bit more.
Yeah I know but Im not good to draw I have to practice more
Thanks for you advice I'm gonna try !