Utz, Jamie – Understanding the tradeoff between safety and food quality in a mammalian herbivore specialist, the Pygmy Rabbit. 2012.
Conserving a sensitive animal species requires understanding the simultaneous tradeoffs between food and shelter within a landscape. Most management approaches only consider single factors like percent cover at landscape spatial scales. Quantifying the synergy between cover and food quality at a scale relevant to a foraging animal could better reveal the forces that shape habitat use. To better understand habitat use components, I investigated tradeoffs between predation risk and diet quality in a sagebrush endemic, the pygmy rabbit (Brachylagus idahoensis). This species is a rare example of a specialist herbivore that relies almost entirely on sagebrush for cover and 50-99% of its diet. I hypothesized that pygmy rabbits would forage in areas with low predation risk and high quality food, but would trade off lower predation risk for higher quality food. I compared food intake of pygmy rabbits during three double-choice trials designed to examine tradeoffs by varying the levels of predation risk (cover) and food quality (toxicity). Rabbits ate under dark cover and preferred non-toxic food. However, interaction results suggested 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 suggested strong variation in tolerance of toxins or predation risk. Preliminary field studies also show that heterogeneity of cover and diet quality in the sagebrush landscape can influence habitat use by pygmy rabbits, creating the potential for tradeoffs between cover and food quality. I measured physical and chemical plant characteristics to map habitat heterogeneity, and measured pygmy rabbit use of each plant using counts of fecal pellets. These measurements allowed me to estimate how pygmy rabbits are responding to microhabitat heterogeneity in their landscape. Interactions between cover and diet quality can influence risk associated with foraging and ultimately shape habitat use and should be considered in management decisions for pygmy rabbits and other mammalian herbivore specialists.