Bird intelligence deals with the definition of intelligence and its measurement as it applies to birds. The difficulty of defining or measuring intelligence in non-human animals makes the subject difficult for scientific study. Anatomically, birds (the 10,000 species of which are the direct living descendants of, and so are, theropod dinosaurs) have relatively large brains compared to their head size. The visual and auditory senses are well developed in most species, while the tactile and olfactory senses are well realized only in a few groups. Birds communicate using visual signals as well as through the use of calls and song. The testing of intelligence is therefore based on studying the responses to sensory stimuli.
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