The exact number of bird species in the world can change as new species are discovered, and taxonomic revisions occur. However, as of my last knowledge update in September 2021, there were approximately 10,000 to 11,000 recognized species of birds worldwide. Bird taxonomy is an evolving field, and ongoing research can lead to changes in the classification and naming of species. For the most up-to-date information, it's best to refer to resources like the International Ornithological Congress or organizations focused on bird conservation and research.