Upon publication of this article [1] it has been noted that due to a technical error the publisher missed to include the Open Access Licence statement in the copyright line. The correct copyright line should have read: © 2015 Pears et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.