I read this book in the 80’s in my elementary school library. Large, detailed paintings, rendered realistically, of little cartoon-ish humanoid people dressed in WWI type clothes and gear. They lived and fought in the forest and used animals as we would use machines. I remember the pictures always showing both sides trying to get the upper hand on one another in each picture, and one wore WWI German type gear, while the other side wore British.
One picture was a guy riding a sparrow, dressed as a fighter ace, the sparrow having a intricate harness to hold the rider and two maxim machine guns mounted to its back. He is looking behind him, or below at the opposing Sparrow pilot.
I have included sketches of what I remember.
I’m pretty sure that you’re remembering one of the “Trumpets” books by Peter Cross. If you follow the link below and scroll down, at the bottom of the page on the right you’ll see one of the illustrations of someone riding a bird done up like a fighter plane, just as you describe (though this particular illustration looks like a starling rather than a sparrow).
https://petercrossart.com/books/trumpets/trouble-for-trumpets
This book has been a Stumper before – evidently once seen it remains with people!
This is it! I forgot about the hot water bottles! Thank you so much!!!
Oh wow I forgot about the hot water bottles! This is it, Thank you so much!
I’m so impressed by your sketches! They totally captured the style of the illustrations. I can’t draw anything without the reference right there…