We evaluated the performance of two GPS collars as a tool for studying Japanese black bears (Ursus thibetanus japonicus) in the Kanto region, Japan. Collars were placed at five stationary points to test the effects of GPS antenna orientation and degree of canopy closure on the fix rate and the positional error, and collars were deployed on 16 free-ranging bears to examine the fix rate and the effects of fix interval on fix rate. In the stationary tests, the proportions of no fix and of 2D fix (vs. 3D fix) increased as canopy closure increased and antenna orientation was further from vertical; at an antenna angle ≥90° from the vertical and canopy closure of 76.2–79.1%, the fix rate was <50%. The positional error for 3D fixes (ranged from 6.84 to 16.43 m) was significantly lower than that for 2D fixes (ranged from 30.74 to 43.45 m), and the positional error for both was affected by canopy closure and GPS antenna angle. An expected multipath effect on positional errors by rain was not statistically significant. Mean fix rates on collared bears ranged from 23.6% to 56.4% and were significantly lower than those in the stationary test. The fix rates at 5-min intervals were significantly higher than those at 4-hr intervals. Although our tests revealed some limitations and biases, GPS collar appears suitable for studying the movement and behavior of the bears.
Defecation time, fecal amount, and water content of feces of sika deer, Cervus nippon, were studied for two deer kept in large-scale enclosures. The deer were observed eight times for 24 hours, and all the feces were collected immediately after defecation. The defecation interval varied considerably with a median of 21 min. The number of defecations per 24 hours ranged from 9 to 49. The number of fecal pellets per deer per 24 hours showed a seasonal variation with a mean of 1276. As a parameter for the fecal pellet count method, our result did not conflict seriously with the number, 1010/deer/day, obtained from captive deer (Takatsuki et al. 1981) on the average basis. On the other hand, its seasonal variation has to be considered when a deer population is censused with pellet count method. Water content of fecal pellet varied widely with apparent response to precipitation within three days before the defecation.
In rodents, an adaptation for biting off hard materials, accompanied by extension of the masseter origin anterior to the orbit, might interfere with vision in the anteroventral direction. In arboreal rodents, the anatomy must be modified somewhat to allow for the clear anteroventral vision necessary to safely descend from, or move about on trees. In the present study, we tested this hypothesis by comparing the craniometric data between two Apodemus murids, semiarboreal A. argenteus and terrestrial A. speciosus. Based on the correlation between the index of relative encephalization (IRE; cube root of the brain case volume divided by the basicranial length) and the angle of the foramen magnum, the head in A. argenteus is situated so that the snout is more depressed than in A. speciosus, which has the same IRE value. The head posture of A. argenteus does not seem to be due to the relative brain size, but rather to a semiarboreal adaptation that ensures clear anteroventral vision by lowering the anterior portion of the masseter to a greater degree than the eyeball.
Shipley et al. (1994) theoretically and empirically demonstrated that the maximum feeding rate of mammalian herbivores (mainly ungulates) is largely determined by morphological factors and ultimately by body mass. By using values from the published literature, I conducted the scaling of 2 indices of feeding rate with body mass in wild primates: (1) the maximum and (2) the mean of dry weight intake rate (g/min) of different food items. The maximum feeding rate scaled with body weight to the power of nine-tenths to one. Body mass accounted for 57% to 71% of the variance in maximum feeding rate. Compared with Shipley et al.’s (1994) regression equation, primates exhibit a higher maximum feeding rate than ungulates of the same body mass. This might be due to the frugivorous nature of the primate diet. Further, the average feeding rate also scaled with body weight to the power of one-half to seven-tenths. Body mass accounted for 34% to 40% of the variance in average feeding rate. The observed body mass-dependent average feeding rate is due not only to the morphological constraints of small body mass but also to the selection of a diet with a higher feeding rate in large-bodied primates.
The nutritional conditions and dietary profiles of Japanese black bears that intruded into residential areas in Hiroshima, western Japan, in autumn 2004 were estimated. Nutritional conditions were evaluated using a morphometric index, the body-condition index (BCI) deduced for the American black bear, which has similar morphology and physiology to the Japanese black bear. The BCI had a wide range, from –3.0 to 3.5, indicating a wide range of nutritional conditions of the bears. There were no significant effects of age class, sex, or month of capture on the BCI. Dietary profiles were estimated by measuring the carbon and nitrogen stable isotope ratios (δ13C, δ15N) of bear hairs, which archive information on dietary changes during the growth of the hair. These values indicated wide-ranging diets that included C3 plants, animal matter, and anthropogenic food, and identified marked individual differences in dietary profiles. Individuals with a high BCI tended to consume high-δ15N food such as animal matter and acorns. Because the proportion of individuals that acquired the high-δ15N food was small, the amount and distribution of such food items might have been restricted and subject to competition among bears in Hiroshima in autumn 2004.