We owe special thanks to the P.A. Hens Memorial Fonds which funded this study, thus enabling the first author to work in the Leiden collection. Furthermore we would like to thank the collection manager of birds and mammals, Hein van Grouw, for his technical support in the collection. Last but not least we are grateful to Edward Dickinson and David Wells for their thorough reviews and helpful comments on this paper.
Edited: L.P. van Ofwegen