Partridge flank feathers

[Darwin]

Here are a couple of page that might give you a few ideas.
http://caledoniaflies.co.uk/caledoniafly/index.php?main_page=index&cPath=66_92

http://frankiemcphillips.com/category/104/wet-mayflies.html

http://www.caithnessqualityflies.co.uk/Mayflies.html