Serum proteins were studied to clarify interrelationships of seemingly disjunct herds of feral donkeys (Equus asinus) in the mountains of Death Valley National Monument, California. Sera of 162 donkeys from five localities in the Panamint Mountains were examined by starch-gel electrophoresis to assess polymorphic variation in transferrins. Four homozygous and six heterozygous transferrin phenotypes controlled by four codominant, autosomal alleles were identified with Fe59 autoradiography. Significant interlocality heterogeneity in genotype distribution and allele frequency distribution among herds was demonstrated. The maximum distance between adjacent herds was 52 km and the minimum distance was 14 km. There are no major physical barriers to movements between herds; furthermore, donkeys are highly mobile animals capable of extensive travel. Behavioral isolation of adjacent herds occurs from May through July, during the peak of reproduction. This isolation is reinforced by fidelity of individuals to their respective home ranges, and to physiological dependence on permanent sources of water. Adjacent herds may overlap during winter when breeding and dependence on water sources are reduced.
