麻豆淫院

Feeding signs give researchers information about ecology in a given area. Feeding signs also provide information on animal distribution, habitat selection, and abundance. But feeding signs do not necessarily reflect the distribution or density of animals directly. In addition, it is difficult to recognize the presence of endangered species only from feeding signs. Thus, scientists need to understand the factors and environmental conditions that influence the formation of feeding signs.

Most habitats of the Asiatic black bear (Ursus thibetanus) in Japan are close to human settlements, so monitoring bear densities helps to predict bear intrusions and decrease conflict between humans and bears. Because bears live in forests in low densities, it is difficult to find them. Therefore, to estimate bear density, feeding signs are useful.

Arboreal feeding signs (AFSs) are noticeable field signs made by Asiatic black bears. When bears feed on trees, they break branches in the tree crown to acquire fruits or leaves that are attached to the branch tips. Thus, AFS is characterized by broken branches piled in the tree tops and branches, which look like birds' nests. Some local governments in Japan have used observations of AFS as indicators of bear density. However, it is unknown whether AFSs are related to bear density and what kinds of factors may influence AFS formation. For example, bears climb and eat hard mast (i.e. create AFS) before the fruits are ripened and quantity of hard mast do not reach maximum value.

Here, the researchers studied the influence of fruit production of individual trees and at regional scale on the detection of AFS to determine in what case bears climb to eat hard mast. For seven years, the researchers counted the number of fruits for 374 to 481 trees each year for three dominant hard mast species (Quercus crispula, Quercus serrata, and Castanea crenata) in the Ashio-Nikko Mountains of central Japan. They estimated individual tree energy values and regional mast energy values by averaging energy values of all three species annually. The scientists also checked for the presence or absence of AFS in these trees, and analyzed the influence of factors such as individual tree energy and regional mast energy on the detection probability of AFS.

AFS were found to be more likely in individual trees with larger mast energy values. This indicates that climbing may be costly for bears, and so they climb only trees bearing many fruits to maximize feeding efficiency. Because bears cannot digest fiber efficiently, quantity may be especially important for feeding. Moreover, AFS were created more during poor mast years. In those years, the energy that bears can obtain from climbing a tree is lower, and there is much greater competition for the hard mast on the forest floor with other animals, such as mice. In good mast years, bears can eat a lot of mature hard mast without climbing, because fruit will fall to the forest floor.

In poorer mast years, AFS is likely to be created on trees that were not selected in greater mast years. It is probably because the number of trees bearing many fruits decreases. In greater mast years, bears may not climb trees to eat fruits regardless of the amount of individual tree energy.

In conclusion, bears may maximize their feeding efficiency in various ways depending on fruit quantity of individual tree and across the region. In conclusion, AFS cannot be used as an indicator of bear density unless both individual tree energy and regional mast energy values are monitored. To make AFS a reliable indicator of bear populations, comparative studies are essential at sites with similar tree species compositions to the study area and with obviously different bear densities.