 The similar motor constraints on human and avian song may have driven these to have similar song structures, including "arch-shaped and descending melodic contours in musical phrases", long notes at the ends of phrases, and typically small differences in pitch between adjacent notes, at least in birds with a strong song structure like the Eurasian treecreeper.Musicologists such as Matthew Head and Suzannah Clark believe that birdsong has had a large though admittedly unquantifiable influence on the development of music.Birdsong has influenced composers in several ways