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Utz, Jamie – Understanding the trade-off between safety and food quality in a mammalian herbivore specialist, the Pygmy Rabbit (Brachylagus idahoensis)

Utz holding wild rabbitConserving a sensitive animal species requires an understanding of the simultaneous trade-offs between avoiding predators, such as raptors, and finding quality food within a landscape. Most conservation approaches only consider singular factors like percent cover of plants for refuge or diet quality at large, landscape spatial scales. Quantifying the synergistic interaction between refuge from predators and food at a scale relevant to an actively foraging animal could reveal the forces that shape habitat use.

To obtain a better understanding of habitat use components, I investigated trade-offs between perceived risk of predation and diet quality in the pygmy rabbit.  

A sagebrush obligate, the imperiled pygmy rabbit (Brachylagus idahoensis) is a rare example of a specialist herbivore that relies on sagebrush for all of its refuge needs as well as 50-99% of its diet.

Pygmy rabbits are the smallest rabbit species in North America whose high mortality rate is primarily due to aerial predation. As landscapes change and aerial predators gain access to previously inferior hunting grounds through human development (e.g. increased perch sites), the pygmy rabbit faces unprecedented foraging challenges.

To test the driving factors behind foraging and habitat use, I hypothesized that pygmy rabbits would forage in areas with the lowest predation risk and highest quality food, but would trade-off lower predation risk for higher quality food. A series of controlled captive studies revealed that the value of cover can decrease if food quality is low and that the value of quality food can be reduced if cover is not optimal. Furthermore, foraging decisions by individual rabbits suggest strong variation in tolerance to either predation risk or poor food quality. Results show that the interaction between cover and diet quality can influence the risk associated with foraging and ultimately shape habitat use by a mammalian herbivore. The shifting variation in landscape quality and predator profile may yield strong pygmy rabbit conservation implications

Currently, I am replicating the above-mentioned captive trials in a field setting with wild rabbits. These predation risk manipulation trials may reveal the extent to which aerial predation risk influences foraging patterns, ultimately yielding previously undetected driving forces that determine pygmy rabbit habitat use and overall fitness.

Thesis Abstract