www.trakus.org is a reference site containing tens of thousands of photos and lots of accompanying data, which was established to collect and share anonymous information about the birds species that can be found in their natural habitats across Turkey.

www.birdtheme.org is an incredible database where every bird themed stamp can be found. It was the site I referred to the most while putting this collection together – it still is. Simply a boon for those interested in bird themed stamps.

www.bird-stamps.org again, a highly recommended website. It's a data bank encompassing all the bird species in the world. A highly recommended reference site for those interested in collecting bird themed stamps.

www.delcampe.net is an online marketplace and auction house for stamps with trustworthy users that also comes in handy for price-checking.