 Luis Felipe Baptista and Robin A. Keister argued in a 2005 paper "Why Birdsong is Sometimes Like Music" that the way birds use variations of rhythm, relationships of musical pitch, and combinations of notes can resemble music.They consider the theory that birds sometimes exploit variation in song to avoid monotony.They survey bird families that habitually borrow phrases or sounds from other species; the European starling is a well-studied borrower, and it is possible that the species inspired a Mozart piece.