There are literally millions of stamps in this world to collect, one is bound to choose favourite topics to narrow down the search - one of my topics are the animals, especially the endemic and/or endangered species (these two often overlap). The Inaccessible Island Rail (Atlantisia Rogersi) is a small bird of the rail family, the only species in its genus; endemic to Innaccessible Island (an extinct volcano not even 13 square km in size) in the Tristan Archipelago in the isolated South Atlantic, notable for being the smallest extant flightless bird in the world. Its conservation status is Vulnerable.
This is my somewhat belated entry for Sunday Stamps - letter I. There are some amazing entries that you can find following this link.