Below are a bunch of resources you might find useful which I have links to - either as an affiliate or just because I use them regularly. Click the logo to visit their website.
Rosemary & Co
My Reference photos
Wildlife Reference Photos
My go to brushes! I'm proud to be an affiliate for Rosemary & Co; you can click the affiliate link above or enter LISELLEFAEART at the checkout. Professional quality and affordable, Rosemary & Co handmake their brushes here in the UK, but ship worldwide. My most used brushes are the Series 316 Pointed Cat's Tongues, and the Series 230 mini rigger is great for painting whiskers!