Avoiding toxic levels of essential minerals: a forgotten factor in deer diet preferences

Deer activity levels and patterns vary along gradients of food availability and anthropogenic development

Animal activity reflects behavioral decisions that depend upon environmental context. Prior studies typically estimated activity distributions within few areas, which has limited quantitative assessment of activity changes across environmental gradients. We examined relationships between two response variables, activity level (fraction of each day spent active) and pattern (distribution of activity across a diel cycle) of white-tailed deer (Odocoileus virginianus), with four predictors-deer density, anthropogenic development, and food availability from woody twigs and agriculture. We estimated activity levels and patterns with cameras in 48 different 10.36-km2 landscapes across three larger regions. Activity levels increased with greater building density, likely due to heightened anthropogenic disturbance, but did not vary with food availability. In contrast, activity patterns responded to an interaction between twigs and agriculture, consistent with a functional response in habitat use. When agricultural land was limited, greater woody twig density was associated with reduced activity during night and evening. When agricultural land was plentiful, greater woody twig density was associated with more pronounced activity during night and evening. The region with the highest activity level also experienced the most deer-vehicle collisions. We highlight how studies of spatial variation in activity expand ecological insights on context-dependent constraints that affect wildlife behavior.

Do Feed Plants Provide Sufficient Sodium, Calcium and Magnesium to Sika Deer in Japan? An Analysis Using Global Plant Trait Data

Deficient minerals in overabundant populations could act as an attractant to cull sika deer (Cervus nippon). Because selective culling of female deer is reported to be effective in reducing sika deer populations, it is particularly important to clarify the differences in mineral requirements between males and females. Here, using global plant trait data and a published list of sika deer feed plants in Japan, we estimated whether feed plants provide sika deer sufficient sodium (Na), calcium (Ca) and magnesium (Mg), and compared the results between males and females. An analysis of 191 feed plant species suggested that feed plants can provide sufficient Mg, whereas sufficient Na and Ca is not always provided, especially when the intake is small or the deer large. Na deficiency was more intense for lactating females than males, suggesting that Na can be an effective attractant for selectively culling female deer. In summary, this study demonstrated that sika deer in Japan might require extra Na and Ca sources in addition to feed plants, and therefore these minerals could be useful for developing effective culling methods.

Roe deer as a bioindicator: preliminary data on the impact of the geothermal power plants on the mineral profile in internal and bone tissues in Tuscany (Italy)

The European roe deer (Capreolus capreolus) is one of the most abundant ungulate species in Europe. Many studies have investigated its distribution, behavior, and ecology, but few have focused on its role as bioindicators for pollutants, particularly regarding antlers, which has been shown to indicate also deer physiology. The presence of geothermal power plants can induce accumulation of potentially polluting elements (such as Tl, S, and Pb). Thus, we collected roe deer samples from areas of Tuscany (Italy) where power plants are present. They were divided according to whether their home range included areas close or far from geothermal power plants. We analyzed the body measurements and the profile of the minerals in the liver and antlers tissues using the ICP-OES technique. Results showed that livers from roe deer close to power plant accumulated higher quantity of Bi, Co, Ni, Tl, and S compared to controls. Males culled close to geothermal power plants had significantly lower values for weight and chest circumference, and also, the antlers showed higher values for Li and Sr in the first sampling position. Thus, despite the small sample size in this preliminary study, antlers and livers of roe deer seem to be a bioindicator of industrial impact on the environment.

Diet selection of white-tailed deer supports the nutrient balance hypothesis

Herbivores must navigate a heterogeneous matrix of nutrients in plant communities to meet physiological requirements. Given that the only difference between an essential nutrient and a toxin is the concentration in the herbivores diet, heterogeneity of nutrient concentrations in plant communities likely force wild herbivores to balance intake of abundant nutrients that may reach toxic levels with the need to meet nutritional demands of rare nutrients (i.e., nutrient balance hypothesis). While this hypothesis has been demonstrated in controlled studies with captive herbivores, experiments testing the nutrient balance hypothesis with wild herbivores are rare. We designed a cafeteria-style experiment to measure use of forages with differing nutritional compositions by wild white-tailed deer (Odocoileus virginianus) to test the nutrient balance hypothesis. We predicted deer diet selection would be explained by attraction to some nutrients and avoidance of others. Deer selected forages with low sulfur concentrations, a nutrient that commonly reaches toxic levels in herbivores. However, deer secondarily selected forages with greater digestibility and crude protein. Thus, our data indicate that the nutrient balance hypothesis may explain diet selection in wild herbivores where they avoid reaching toxicity of abundant nutrients while secondarily maximizing intake of limiting nutrients.

Ecological effects of game management: does supplemental feeding affect herbivory pressure on native vegetation?

Context Supplemental feeding of large mammalian herbivores is a common management tool mainly aimed at promoting healthy populations and at increasing productivity and trophy sizes. Such management measure may indirectly affect herbivore effects on plant communities through altered foraging patterns. The quantification of the ecological effects of large herbivore management is important for designing holistic management and conservation programs. Aims Here we aimed at quantifying the ecological effects of supplemental feeding of Iberian red deer, Cervus elaphus hispanicus, on the composition of and on the browsing effects on Mediterranean woody plant community. Methods An experiment was set up in a hunting rangeland located in central Spain, where female deer were kept in enclosures with either exclusive access to natural forages or with additional ad libitum access to a nutritionally rich concentrate. The experiment also included a control area where deer were absent. Key results We observed significant differences in browsing impacts among the supplemented, non-supplemented and control areas, and such effect varied for the different plant species. Plant species which nutritional content complemented that of fodder were more highly consumed, for instance, Erica spp., which digestible fibre content is higher and N content lower than that of provided fodder. The presence of deer and the concentrate supplied, instead, did not influence the relative abundances of shrub species. Conclusions Artificial supplemental feeding provided to ungulates led to increased browsing on plant species which nutritional composition complemented that of the supplement provided. Implications So as to alleviate herbivory impact on all shrubs, we suggest that composition of supplemental feeding should adjust both to the natural forage availability and quality and to ungulate requirements across seasons.