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The evolution of the sense of touch in birds: the role of the avian tactile bristle


The sense of touch was a cornerstone in mammalian evolution. It is one of the most specialised sensory systems, driving brain complexity and behavioural flexibility. Some bird species also possess tactile sensors that are analogous to mammalian whiskers; however, they have been largely overlooked by researchers. These sensors take the form of rictal bristles, a type of facial feather present notably in the Caprimulgiformes order (Nightjars and related species). This study is the first step in characterising bristle morphology and anatomy in birds, focussing especially on the Caprimulgiformes. 183 specimens were measured from 61 nightjar species at Tring Natural History Museum and it was found that bristle features (thickness, branching, and length) varied greatly between species, with no clear evolutionary pattern occurring within the nightjar phylogeny. Anatomical work on two closely related African nightjars (Pennant-winged and Fiery-necked) showed large variation within the rictal bristle follicle. The Pennant-winged nightjar had intrinsic muscle fibers around bristle follicles, whereas the Fiery-necked nightjar had intrinsic collagen fibers and mechanoreceptors. Despite the difference, the presence of intrinsic fibers suggests that the bristles may well be moveable, and the mechanoreceptors reveal their role in touch sensing. The next step will be to characterise the neuroanatomy to assess whether the brain structure and connections also varies greatly between these two related species. Future studies, within the PhD, will expand this work further, by firstly investigating other bird groups to see how and why rictal bristles might be present in certain species; and secondly defining bristle-use during foraging.


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