The Relationship of Water Content, Seed Selection, and the Water Requirements of a Heteromyid Rodent

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Abstract
Kangaroo rats are mainly granivores, and some species store large amounts of seeds in underground caches. These desert rodents do not drink free water under natural conditions but instead rely on preformed water in their diet and metabolic water produced by food oxidation. Moisture content may therefore influence kangaroo rat seed selection. Feeding experiments were conducted to determine both the effects of water content in seed preferences by Dipodomys spectabilis and the minimal preformed water requirements of these rodents. Results demonstrate that the minimal seed water content for a positive water balance is 10%-11% wet mass, under laboratory conditions. These rodents can sense a 6.05% difference in water content and always prefer the moistest seeds available, even when selecting among seeds containing over twice the minimal water necessary for a positive balance. These results indicate that kangaroo rats do not ingest only enough preformed water to meet their requirements but instead maximize water intake through their seed preferences.