ctive overhead protection,
while the ground beneath was relatively open. Houses built in the
thickets were so well concealed that they were usually not detected
until after leaves were shed in autumn. In most cases the blackberry
thickets were small and well isolated. Houses of the rats were sometimes
unusually near together suggesting that these thickets provided
especially favorable habitat conditions.

Hollow trees are often utilized, the accumulation of sticks for the
house being largely inside the cavity. To be suitable for a house site,
the snag must have an opening near ground level, and another higher on
the trunk, providing emergency outlets in two directions. Most of the
hollow trees utilized were black oaks (_Quercus velutina_).

In 1948 there were many houses in cut tops of trees left from small
scale lumbering operations a few years earlier. The densely branched
tops of elms, oaks and hickories had satisfied the requirement for
support of the house and nearby shelter. The houses built in them were
in open woodland well separated from otherwise favorable situations. By
1948 the tops were disintegrating and no longer provided effective
shelter. The houses built in them were falling into disrepair and were
not permanently inhabited but were often used temporarily by wandering
individuals.

Along cut banks of gullies where trees were partly undermined by
erosion, the exposed, tangled root systems provided sites for occupancy.
In these situations the accumulations of sticks were small and lacked
the typical domed shape, consisting essentially of a lining to the
cavity beneath the roots.

Two small buildings at the Reservation headquarters were accessible to
woodrats and were utilized off and on throughout much of the period of
this study, despite the fact that most other sites of occupation away
from the hilltop outcrops were deserted in the same period. One small
building used as a laboratory had an enclosed wooden box five feet
square housing an electric water pump. The interior of this box was
accessible to the rats from beneath the floor. Litter of sticks and
stems and various food materials were carried in by the rats. The nest
thus protected and enclosed was not surrounded by the usual accumulation
of sticks. An old garage 30 feet from the laboratory building was also
occupied, sometimes by a different individual. The nest and food stores
were behind boards propped against the wall.

In October, 1948