Effect of Sodium on Seed Choice by Deer Mice, White-Footed Mice, and Hispid Cotton Rats

Abstract

Effect of sodium content on seed use was tested for deer mice (Peromyscus maniculatus), white-footed mice (P. leucopus), and hispid cotton rats (Sigmodon hispidus) using sodium-enriched pearled barley seeds (Hordeum vulgare). Each trial included the choice of four types of barley seeds [ 1.6 (control), 4.8, 7.1, and 16.8 mg sodium/g seed]. Seed use by deer mice and whitefooted mice differed with sodium concentration but was not affected by locality (eastern versus central Kansas) or gender. In contrast, seed use by cotton rats was not influenced by sodium content and, although seed use differed between males and females (females tested were larger than the males), relative use of seed types was not affected by gender. Average sodium concentration of seeds used did not differ with locality or gender for either deer mice or white-footed mice, or among deer mice (6.6 mg/g), white-footed mice (5.6 mg/g), and cotton rats (6.2 mg/g). Mammalian herbivores, including ungulates (Dalke et al., 1965; Hebert and Cowan, 1971), lagomorphs (Smith, Latherland, and Myers, 1978), and arvicoline rodents (Christian, 1989; Hansson, 1990), periodically use mineral licks or eat sodium-rich materials. Laboratory tests also have shown a positive effect of sodium on food choice by small herbivorous rodents (Batzli, 1986). Further, use of sodium-soaked wooden pegs presented to free-living fox squirrels (Sciurus niger) and woodchucks (Marmota monax) demonstrated a positive sodium response by both of these sciurid rodents (Weeks and Kirkpatrick, 1978). We tested use of NaCl-rich foods by free-living deer mice (Peromyscus maniculatus), white-footed mice (P. leucopus), and hispid cotton rats (Sigmodon hispidus). Because one cannot determine which small, free-living species of rodent has fed on test materials placed in natural environments, we used a chamber, essentially a large live trap, in which test foods were SCorresponding author. This content downloaded from 157.55.39.163 on Wed, 21 Sep 2016 04:39:04 UTC All use subject to http://about.jstor.org/terms 144 TRANSACTIONS OF THE KANSAS ACADEMY OF SCIENCE available to trapped rodents. Our objectives were to test for an effect of sodium content on food use by these small rodents and possible interspecific differences in food choice related to sodium content. We expected rodents to eat sodium-enriched seeds but not to maximize sodium intake by eating only our highest sodium-enriched seeds (a concentration several times greater than natural seeds). We also expected a greater sodium content in ingested seeds for the cotton rat, a herbivore, than deer mice and white-footed mice,