International Migratory Bird Day

According to different estimates, there are 9,800 to 10,050 bird species in the world today. Modern birds are included into the subclass of Ornithurae or Neornithes, which is contrasted to Saururae or Archaeornithes. The archaeopteryx is only species in the latter group.
Ornithurae are subdivided into 2 subclasses including 33 orders (6 of them only with fossil forms) and 213 families (42 of them extinct). There 9,000 species grouped into 2,000—2,400 kinds. They are found across the world.