Additional file 1.

Syringeal skeleton of the male and female zebra finch syrinx (interactive 3D PDF). This 3D PDF figure can be viewed with Adobe Acrobat Reader version 9 or higher (http://www.adobe.com webcite). Click on the figure to activate the 3D features. Tyzack [121] provides a comprehensive introduction to the use of interactive 3D PDF files, while Kumar and colleagues [69,122] provide instructions on how to create interactive 3D PDF files.

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Düring et al. BMC Biology 2013 11:1   doi:10.1186/1741-7007-11-1