Understanding Tradeoffs Between Food and Predation Risks in a Specialist Mammalian Herbivore

Understanding habitat use by animals requires understanding the simultaneous tradeoffs between food and predation risk within a landscape. Quantifying the synergy between patches that provide quality food and those that are safe from predators at a scale relevant to a foraging animal could better reveal the parameters that influence habitat selection. To understand more thoroughly how animals select habitat components, we investigated tradeoffs between diet quality and predation risk in a species endemic to sagebrush Artemisia spp. communities in North America, the pygmy rabbitBrachylagus idahoensis. This species is a rare example of a specialist herbivore that relies almost entirely on sagebrush for food and cover. We hypothesized that pygmy rabbits would forage in areas with low food risk (free of plant secondary metabolites, PSMs) and low predation risk (high concealment). However, because of relatively high tolerance to PSMs in sagebrush by pygmy rabbits, we hypothesized that they would trade off the risk of PSM-containing food to select lower predation risk when risks co-occurred. We compared food intake of pygmy rabbits during three double-choice trials designed to examine tradeoffs by offering animals two levels of food risk (1,8-cineole, a PSM) and predation risk (concealment cover). Rabbits ate more food at feeding stations with PSM-free food and high concealment cover. However, interactions between PSMs and cover suggested that the value of PSM-free food could be reduced if concealment is low and the value of high concealment can decrease if food contains PSMs. Furthermore, foraging decisions by individual rabbits suggested variation in tolerance of food or predation risks

Effects of resource availability on sex allocation in herbivores

For well over a century, ecologists have attempted to understand the evolutionary pressures shaping the allocation of resources to offspring of different sexes but support for competing theories remains inconclusive overall. Most empirical studies with mammals have been performed on free-ranging animals where researchers are unable to control environments or to trace the line of individuals over multiple years. At Washington State University and Starkey Experimental Forest and Range in Oregon, we set up nutritional trials to test the effects of body mass, body condition, and diet on the birth sex ratios of two species of polygynous mammals: mule deer (Odocoileus hemionus) and elk (Cervus elaphus). Despite carefully controlling and measuring nutritional resources, we found little evidence that forage quality or body fat near breeding influences birth sex ratio (BSR) of female mule deer and elk, or the probability that a neonatal elk or mule deer would be certain sex. However, in our sample of 76 mule deer fawns, we found that digestible protein intake influenced the probability of having a male fawn. Similarly, although BSR of females treated with GC was absolutely higher than those treated with a placebo (0.71 vs. 0.50), BSR were not statistically different and corticosteroid treatment did not predict the sex of a fawn. In addition to analyzing the preexisting data, we used another herbivore, Grammia nevadensis, to test how growth rate, population density and diet affect sex ratio of offspring. We used high protein, low fiber kale and a low protein, high fiber pelleted diet to explore how these various diets affect other life-history traits of G. nevadensis. Despite the benefits of using G. nevadensis as a model species to test sex allocation hypotheses, we found little evidence that forage quality, average number of days till pupation or average number of days to emergence affected population sex ratios. Forage quality did, however, affect growth rates and the average number of days till pupation or emergence. Our results illustrate the difficulties in testing evolutionary hypotheses such as TWH in wild ungulates and herbivores in general

Cache like a Squirrel: Effects of Long Term Storage on Crude Fat Content of Q. Palustris and Q. Alba Acorns

Quercus palustris and Quercus alba acorns are a primary component in many wild animal diets, particularly during preparation for winter. As such, they provide a natural, easily gathered food staple for wildlife recovering in rehabilitation facilities. We examined whether collection and temperature-controlled storage methods differentially affect the nutritional deterioration of crude fat in acorns to assess both caching by wildlife and to provide recommendations to rehabilitators. We collected acorns from Q. palustris in 2020 (N=8) and Q. alba in 2017 (N=11) in Bridgewater, VA, USA. Acorns were dried for 7 days using a fan or for 30 minutes in an oven at 93°C and then stored at room temperature hanging in onion bags, in the refrigerator, or in the freezer. We assayed fat content from all trees immediately after collection (baseline) and compared fat content after one month and six months of storage for both species. Storage at 4°C (refrigerator) resulted in germination of some Q. alba acorns and mold growth in both species. Although acorns from Q. palustris had significantly more fat than Q. alba acorns, individual trees varied widely, with greater variation among Q palustris. On average, drying, storage, and combination treatments resulted in greater losses in fat compared to baseline for Q. alba than Q. palustris, but not significantly. Our results suggest that acorns cached by species like squirrels (Sciurus sp.) do not vary significantly in fat content when recovered months later compared to acorns consumed directly from the trees. We recommend wildlife rehabilitators store acorns either in the freezer or at room temperature depending on their storage capabilities