From 2001 to 2007, Majerus carried out experiments in Cambridge to resolve the various valid criticisms of Kettlewell's experiment. During his experiment, he noted the natural resting positions of peppered moths. Of the 135 moths examined over half were on tree branches, mostly on the lower half of the branch, 37% were on tree trunks, mostly on the north side, and only 12.6% were resting on or under twigs. Following correspondence with Hooper he added an experiment to find if bats, not birds, could be the main predators. He observed a number of species of bird actually preying on the moths, and that differential bird predation was a major factor responsible for the decline in "carbonaria" frequency compared to "typica". He described his results as a complete vindication of the natural selection theory of peppered moth evolution, and said "If the rise and fall of the peppered moth is one of the most visually impacting and easily understood examples of Darwinian evolution in action, it should be taught. It provides after all the proof of evolution."