Shariar
Try Sealy et al (1997) Nitrogen isotope ecology  in southern Africa:
implications for environmental and dietary tracing. Geochim.
cosmochim acta 51, 2707-2717.
It contains a fair amount of data from arid southern African
environments.
Ambrose, S. (1991) Effects of diet, climate and physiology on
nitrogen isotope abundance in terrestrial foodwebs, J archaeol. Sci,
18, 293-317, is a review which has plenty of references.

Dr Julia Lee-Thorp
Department of Archaeology, Faculty of Science
University of Cape Town, Private Bag, Rondebosch 7701
South Africa
Tel. 027-21 6502350
Fax. 027-21 6502352