There are around 10,000 living species of birds. All present species inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the 5 cm Bee Hummingbird to the 2.75 m Ostrich. Some birds, especially parrots, are among the most intelligent animal species; a number of bird species have been observed manufacturing and using tools.
Many species undertake long distance annual migrations flying thousands of miles. Birds are social; they communicate using visual signals and through calls and songs. Currently about 1,200 species of birds are threatened with extinction by human activities.