I have not been able to sketch in the field yet as it is winter (Mid-February), but I noted some good suggestions from other users below (folding stool, cotton sock etc). Instead, I practiced with a reference picture of a bay-breasted warbler, that spent the 2022 summer in the woods back at the cottage. I followed the same steps that Liz used to paint the waxwing. I had fun mixing this palette of colours, and adding a leafy background.