Mammal Study

The Asian house shrew (Suncus murinus) is a commensal species whose has become widespread across the Old World due to human activities. This species has been well studied in captivity as a laboratory animal; however, in the wild, its ecological habits are not well investigated. We conducted radio-telemetry surveys to determine home range, habitat selection, and activity patterns of the Asian house shrew over 1 week in September 2012 on Okinawa-jima Island, Japan. The home range size of male shrews was 2,556 m² on average. The shrews were nocturnal, and they exhibited repetitive cycles of active and inactive during the night. The shrews did not move from dens during the daytime, although a few brief activities were observed near dens. Shrews favored grassland habitat as a nocturnal activity place (presumable foraging sites), whereas they favored under floors of artificial constructions as den sites. Our results suggest that Asian house shrews live in near human residential area to obtain the favorable den sites, and they do not absolutely need food resources from human activities for their settlement.

The scats of Lontra longicaudis are easily recognized in the field and provide basic information about its foraging ecology. Two questions were addressed regarding its diet: (I) Does the composition of prey vary temporally? (II) Does the dietary breath vary seasonally? We answered these questions based on scatological analyses. We carried out 12 field trips, once per month for a year, to collect scats along a 13-km stretch of the lower Arroio Grande River in southern Brazil. Scats were collected individually and identified by date and geographic location. Prey items were classified according to food category and to family level. The feeding habits of L. longicaudis were based on fish, with a narrow diet range. Members of the families Cichlidae and Callichthyidae predominated in the diet, and this proportion did not vary during the year. The fish species varied seasonally but the dietary breadth did not. Thus, L. longicaudis hunts, preys, and maintains a degree of feeding flexibility throughout the year.

We studied two groups of food-enhanced long-tailed macaques (Macaca fascicularis) that derived a quarter and half of their respective diets from anthropogenic food resources through human provisioning and feeding at refuse sites. The macaques alternated between feeding on natural food in the forest and feeding on anthropogenic food in adjacent urban areas. We found that dietary compositions of the macaques were correlated to natural fruit availability and macaques fed on natural fruits when available; but activity, habitat use and ranging patterns were correlated more to food availability from refuse sites and provisioning. Higher feeding on anthropogenic food resources was not correlated to natural fruit resource scarcity. Natural fruits constituted a highly variable resource base over the year and anthropogenic food resources provided a potentially more stable, albeit more opportunistic resource base. These results showed that the main drivers for macaque exploitation of anthropogenic foods were unlikely to be either natural food resource scarcity or a high dependence on anthropogenic foods. Behaviors associated with macaque anthropogenic food resource exploitation amplifies opportunities for undesirable interactions between macaques and humans. Addressing the accessibility of anthropogenic food resources to macaques through management intervention should be a priority for mitigating human-macaque conflict issues in Singapore.

By using skulls of sperm whales (Physeter macrocephalus), we analyzed the relative growth of skull length in relation to that of body length. We also analyzed the growth of various parts of the skull in relation to skull length. We used data of 3 males and 1 female collected off the coast of Japan and those of 4 males reported previously. In males, the proportion of skull length to body length increased with growth from 26% (body length, 10 m) to 32% (body length, over 16 m, most of which were considered as physically mature). In contrast, the proportion reached less than 25% in the physically mature female. In males, the relative length of the rostrum and the mandible to skull length increased with growth, and the posterior margin of the occipital bone tended to protrude posteriorly. This posterior protrusion could be considered as a secondary sexual dimorphism observed only in the skull of physically mature males. These characteristics would be associated with sex differences and deep diving as well as to the life style and breeding strategy of sperm whales, a species in which males physically compete for breeding rights.

Recent advances in multivariate statistics, and in ancient DNA techniques, have greatly increased understanding of tiger phylogeography. However, regardless of advances in analytical methodology, researchers will continue to need access to specimens for morphological measurements and sampling for genetic analysis. The tiger has become increasingly endangered, and out of the nine putative tiger subspecies, three (Javan, Balinese, and Caspian) have become extinct in the last 100 years, leaving the specimens kept in natural history collections as the only materials available for research. Frustratingly little information is widely available concerning the specimens of these extinct tiger subspecies. We conducted an extensive search for specimens of extinct tiger subspecies, and also developed a simple on-site method to assign unprovenanced and probable Indonesian specimens to either Javan/Balinese or Sumatran subspecies. We located a total of 88 Javan, 11 Balinese, and 46 Caspian tigers, including seven new Javan tigers, and three Balinese tigers that were not widely known previously. These specimens are critical for research in order to understand the intraspecific phylogeny and evolutionary history of the tiger.

Diet preferences of three captive northern fur seals for seven prey items (Okhotsk atka mackerel, rainbow trout, common mackerel, walleye pollock, Pacific sand lance, horse mackerel, and Japanese common squid) were measured through repeated two-choice tests. Preference indices estimated from the paired consumption data using the normal Bradley-Terry model revealed the existence of diet preferences and their individual variation. The three seals generally preferred Okhotsk atka mackerel, rainbow trout, and common mackerel, but showed individual differences for less preferred food items. The preferred items had moderate food size and high energy content per one item. Once diet preferences were determined, animals were given rainbow trout laced with lithium chloride (LiCl) to induce conditioned taste aversion (CTA). Four to five LiCl treatments were required for CTA, but could only induce temporary aversion of rainbow trout in favor of horse mackerel. Choice tests after CTA demonstrated a decrease in preference indices for rainbow trout in the three animals, but the ranking and preference indices of rainbow trout did not fall below those for horse mackerel. These results suggest that preference and aversion are relative phenomena, and the success of CTA is dependent on the reduction of preference relative to other food items.

Habitat selection is a hierarchical process in which animals select resources at varying spatial scales. Dens are a critical component of American black bear (Ursus americanus) habitat, yet scale-dependent den-site selection has received limited attention. Using habitat and topographic characteristics, we assessed scale-dependent den-site selection by 11 black bears during 20 den years in Mississippi, USA, at 3 spatial scales: den site (15 m), den area (100 m), and den landscape (1,000 m). Black bears in Mississippi exhibited scale-dependent den-site selection selecting greater percentage horizontal cover at the den area scale. Risk of flooding (i.e., elevation, distance to nearest stream), disturbance (i.e., distance to nearest stream or road), and habitat composition did not influence den-site selection at spatial scales measured. Greater percentage horizontal cover likely provides additional security and increases energetic efficiency. Selection for horizontal cover at finer spatial scales suggests security at den sites is a lower-order factor influencing fitness.

The cervical and thoracic regions including vertebrae, spinal nerves, and brachial plexus were examined by macroscopic and three-dimensional computed tomography observational scans in the two-toed sloth (Choloepus didactylus). This species possesses seven cervical vertebrae unlike closely related sloths, which possess varying number of cervical vertebrae ranging from five to ten. The large axis and the partially vestigial third cervical vertebra are morphologically characteristic of C. didactylus. In addition, the spinal nerve branches of C5, C6, C7, C8, and T1 contributed to the brachial plexus, whereas C4 and T2 did not supply nerves to the plexus. Histological data showed that the branches of C5, C6, C7, and C8 were obviously thicker than that of C4 and T1. The most notable observation was that only the two-toed sloth unlike other sloth species is conservative in these morphological characteristics regarding the cervical vertebrae spinal nerves. By comparing the morphological patterns of the cervical and thoracic spine and the brachial plexus of the two-toed sloth with ancestral morphological patterns and related species, which have derived a repatterned and variable morphology of these structures, it is possible to elucidate the morphological evolution of the cervical and thoracic regions in the evolutionary history of these mammals.