First review and synthesis paper on feather fault bars. A model is proposed to link fault bar severity with the propensity to produce fault bars and the intensity of the perturbation. This study helps to explain contradictory results in the literature, to identify knowledge gaps, and to suggest further studies. Authors discuss that fault bars may be a key element to understand other aspects of avian evolutionary ecology, such as the physiology of moult, the integration of moult into avian life cycles, the strategies used by birds to minimize stress during moult, and the evolution of bird flight. informacion[at]ebd.csic.es: Jovani and Rohwer (2016) Fault bars in bird feathers: mechanisms, and ecological and evolutionary causes and consequences. Biol Rev doi: 10.1111/brv.12273