Variation in renal structure and urine concentrating capacity among ground squirrels of the Spermophilus townsendii complex (Rodentia: Sciuridae).

Renal structure and urine concentrating capacity varied significantly among nine populations of desert ground squirrels representing four closely related taxa. Variation in renal structure was weakly associated with taxonomic grouping. Urine concentrating capacity was not correlated with standard measures of habitat were aridity, but it was correlated with soil salinity. Maximum urine osmolalities for one population from the most saline habitat were among the highest documented for sciurid rodents. Results do not support the hypothesis that hibernating sciurids have poor renal efficiency.