Firstly i duplicated the duck and flipped it. I made one smaller and the other one bigger,then i select both then went to object select pattern and make, that saved the pattern into the swatches panel.
On this screenshot i putted together 2 ducks where i made one smaller and the other one bigger. I changed the colour and started using shapes to place my pattern in. As you can see i have mixed the colour green and yellow into 1 shape and the other shapes i done orange and yellow, i didn't go over the top with the colours as i kept it simple.