Sagebrush Characteristics Influencing Foraging Patterns of Pygmy Rabbits

Abstract

The pygmy rabbit (Brachylagus idahoensis) is endemic to the sagebrush steppe landscapes in the western United States. Pygmy rabbits have adapted to this region by depending on big sagebrush (Artemisia tridentata) as a source of nutrition and concealment from predators. Being a central place forager, and a dietary specialist makes pygmy rabbits an ideal subject to study foraging tradeoffs. Our objectives were to determine if pygmy rabbit foraging patterns are influenced by the nutrient content of individual sagebrush, or the size and location of individual sagebrush. We first developed a near infrared spectroscopy assay that can be conducted in the field, with whole plant foliage, to determine individual sagebrush crude protein (CP) and acid detergent fiber (ADF) contents. We then measured the size, location, protein, and fiber contents of >1,500 foraged and non‐foraged sagebrush plants surrounding pygmy rabbit burrows in 2 field sites in northern Utah, USA. We found significant site differences in sagebrush CP levels and significant season differences in sagebrush ADF levels; sagebrush closer to central burrows were higher in protein and lower in fiber. Pygmy rabbits preferred to forage on taller sagebrush plants that were closer to the central burrow but only marginally higher in CP (0.2%) and lower in ADF (1%). Sagebrush plants with a >50% chance of being foraged, were <5.6 m from the burrow, >0.67 m tall, >10.4% CP, and <34.95% ADF. The selection of closer, larger, and more nutrient‐dense sagebrush may be influenced by pygmy rabbits' need for concealment from predators or a way to minimize foraging effort. © 2020 The Wildlife Society.