Besides their physical adaptations that have allowed them to minimize water loss and survive arid climates, Kangaroo rats have developed many behavioral traits that have aided them in their survival in xeric environments. |
Nesting Locations Evaporative water loss from respiration is one of the highest risks of dehydration that Kangaroo rats face. While Dipodomys cannot eliminate water loss from respiration, their nesting habits help to greatly reduce water loss. The amount of water lost during respiration is strongly correlated with the humidity of the air being respired, whereas the moister the air, the less water lost (Schmidt-Nielsen & Schmidt-Nielsen, 1950). In order to increase the humidity of the air they breathe, Kangaroo rats have evolved the tendency to construct elaborate tunnel systems that reach far under the desert surface in which they live. It has been shown that in such environments, relative humidity increases with depth until the air becomes saturated. (Figure 1). Therefore, by utilizing burrows that reach far into the ground, Kangaroo rats are able to create shelters for themselves that are significantly more humid than surface humidities, and reduce evaporative water loss (Figure 2).  
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Figure 1. Variation of Relative Humidity with distance below the surface. The figure shows that as distance below the ground increases, so does relative humidity, until it levels off at 100% when the air becomes fully saturated. Adapted from (Schmidt-Nielsen & Schmidt-Nielsen, 1950)
Temperature Regulation Kangaroo rats are nocturnal animals, and even then only leave their burrows for a portion of the night. While nocturnality in Dipodomys was once believed to be a result of high daytime temperature avoidance, it has been shown that they can survive temperatures of 42.5 °C for up to an hour. Since daytime temperatures rarely get this high, even in the hottest months, nocturnality is thought to be a result of water conservation instead of high temperature avoidance.(Tracy & Walsberg, 2000). While Kangaroo rats have been shown to be able to endure activity at ambient temperatures between 25° - 35° C with little evaporative water loss, water loss increases rapidly at temperatures above 35° C. (Figure 3).
 Figure 2. Absolute Humidities at surface and inside burrows during a 12 hour span. The figure shows that absolute humidities inside the burrows were significantly higher than those at the surface. Adapted from (Schmidt-Nielsen & Schmidt-Nielsen, 1950)
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Figure 3. Evaporative Water Loss in Kangaroo Rats at Different Temperatures. The figure shows that above 35° C, water loss increases rapidly.
Adapted from (Tracy & Walsberg, 2000)