The population density of Japanese sika deer (Cervus nippon yakushimae Kuroda and Okada) in an evergreen broad‐leaved forest in Yakushima, southern Japan, was surveyed over 4 years from 1998 to 2001. Two approximately 50 ha study sites, Hanyama and Kawahara, were established with a total of 4 km of census trails at each site. The estimated densities of sika deer at the two sites were 43–70 deer km−2 at Hanyama and 63–78 deer km−2 at Kawahara, although these values might be underestimates. The adult sex ratio (number of adult males : number of adult females) ranged from 0.6 to 1.0 at Hanyama, and from 0.4 to 0.9 at Kawahara. Mean group size was 1.9 deer (male group, 1.5 deer; female group, 1.6 deer; mixed group, 3.6 deer). The population density of sika deer was relatively high compared to other sites in Japan, with the exception of very small (<10 km2) islands. Possible explanations for this naturally high density of sika deer in an evergreen broad‐leaved forest in Yakushima are discussed.

We observed the feeding behaviors of wild Japanese sika deer (Cervus nippon yakushimae) in a warm temperate broad-leaved evergreen forest of the island of Yakushima using the focal animal sampling Deer also fed on animal matters as minor food items, such as the feces of monkeys and raccoon dogs, bones of deer and monkeys, and bird carcasses. Animal matters constituted 0.3-1.6% of the seasonal diet.Sympatric monkeys supplied food to deer as a result of their daily activities. Monkey-supplied foods 2 comprised 1.7-10.9% of the seasonal diet of sika deer. Monkeys tended to supply many fruits and seeds.Overall, 75.0% of the annual deer diet consisted of forest litter, even though deer had access to abundant living edible leaves in the study area. Therefore, sika deer in this forest ecosystem function ecologically as decomposers rather than primary consumers.

We directly observed the feeding behaviors of Yaku sika deer (Cervus nippon yakushimae), the smallest subspecies of Japanese sika deer, by following 6 wild, habituated, and individually identifiable animals in a natural warm‐temperate forest on the island of Yakushima, southern Japan, 2005–2006. Deer fed on various plant species and parts but predominantly on the fallen leaves, fruits, seeds, and flowers of woody plants (∼82% of food items) at 59 natural feeding plots. We analyzed 8 key plant constituents of eaten and uneaten items at the feeding plots, and examined the effects of each constituent on food selection by multivariate and univariate generalized linear mixed models. The multivariate analysis, which evaluated the effect of each plant constituent on food selection by controlling influences of the other constituents in the food items, showed that deer selected food items with higher contents of crude fat, crude protein, and total phenolics but with lower contents of lignin and condensed tannin from the available items at the feeding plots. Neither soluble nor structural carbohydrate, nor ash content affected selection of food items. It may be advantageous for these small ungulates with shorter gastrointestinal tracts to select foods that are relatively rich in fat because of the higher energy content of fat compared with carbohydrates. Furthermore, it appears that non‐tannin phenolics may have beneficial functions in this species. The univariate analyses showed different effects of crude protein and structural carbohydrate on food selection compared to those derived from the multivariate analysis. We demonstrate that accounting for influences of other plant constituents by using multivariate analyses is important to ensure that any effects of individual plant constituents are not overlooked or overstated. © 2018 The Wildlife Society.

Extraction of DNA from non-invasive samples (feces) has been used increasingly in genetic research on wildlife. For effective and reliable genetic analyses, knowledge about which samples should be selected in the field is essential. For this reason, we examined the process of DNA degradation in feces of deer. We collected fresh fecal pellets from three wild deer living in a warm temperate forest.We then assessed the effects of time (3, 5, and 10 days) under three environmental conditions (on the forest floor, on exposed ground, and inside the laboratory) on the rates of correct genotyping (CG), amplification failure (NA), genotyping error among positive amplification (ER), false alleles (FA), and allelic dropout (AD) of 15 microsatellite loci. The rate of CG significantly decreased, and those of NA and FA increased with increasing lapse of time. Rates of CG tended to be highest and those of NA, ER, FA, and AD to be lowest in feces kept inside, followed by those on the forest floor. Suitability of samples for DNA extraction was lowest in fecal pellets left on exposed ground, and we suspect that rain may hasten DNA degradation. NA rate could serve as a reliable indicator of the quality of fecal pellets because it was significantly positively correlated with ER rate. For efficient genetic analyses using deer feces in warm temperate zones, we recommend collecting fecal pellets within 3 days of defecation, during periods without rainfall and from under the cover of trees.

The accuracy of estimating deer density using the fecal pellet count method is greatly limited by variability of the fecal decomposition rate. The fecal accumulation rate technique can avoid the issue of decomposition rate. However, the precision of this technique is not clear when the decomposition rate is relatively high, such as in Japanese forests. We estimated deer population densities on Yakushima Island by the fecal accumulation rate technique and compared them between seasons. The estimated densities were similar to reported estimates, and did not differ seasonally, in accord with reports that deer on Yakushima do not migrate seasonally. Thus, we conclude that the fecal accumulation rate technique is applicable in Japanese forests.