Drone observation reveals a multilevel society of feral horses

概要

Some mammalian species of various taxonomic groups, including humans, have
developed social structures with nested levels of organization. Individuals are
structured into stable unit groups that preferentially associate with other units to
form a higher level of social organization. This multilevel society is one of the most
complex social structures in animals. The function, mechanism of aggregation,
and evolutionary history of multilevel societies are still poorly understood because
of difficulty in quantitative studies. Even its definition is not quantitatively defined,
and the definition of each hierarchy has often been confused among different
studies. In this study, I applied a drone observation to obtain accurate positional
information of animals, to establish the methodology of quantitative study in a
multilevel society.
Unmanned aerial vehicle (UAV, drone) has been recently used in various
studies in behavioral ecology. The application was limited to a single group, and
most of them did not implement individual identification. However, drones are
suitable for observing large animal groups, and their high resolution of images
enable to detecting social events and identify individuals, thus it has potentials to
study complex animal social group.
I studied on domestic horses (Equus caballus) in a feral condition. The
presence of multilevel societies in feral horses was considered questionable, as no
study has examined whether the units gather to form a social organization or they
are simply together because of the abundance of resources. In each chapter, I
investigated the following three questions: (1) do horses form a multilevel society?
(2) how do they maintain the aggregation of a multiple-unit group? and (3) what
is the genetic background of a horse multilevel society?
2. ...