Acknowledgements
The author would like to express his appreciation to Bisrat Haile, Weldegebriel Hadera and Yirga Halefom for their assistance during the field work, driving through rugged difficult terrains. The running expenses of this study was funded by Mekelle University and Tigray Biological and Biodiversity Association (in kind contribution) through projects: VPRCS/RB/25/2012, VPRCS/RB/20/2012 and CRPO/CNCS/PhD/MU-NMBU/001/2011.