ypical size by the
encroachment of other males. Territorial disputes in this period often
involve physical contact, as well as protracted sessions of
high-intensity singing at rates exceeding three hundred song-phrases
per hour.

Eventually the carrying capacity of the habitat is reached and no
further partitioning occurs. The beginning of nestbuilding coincides
with this relative stabilization of the territorial boundaries.
Through the remainder of the cycle of behavior associated with any one
nest, all activity is that of the occupant pair within its territory.

_Size of Territories_

The nine original territories established in 1960 varied in size from
0.26 acre to 3.1 acres (Table 2). Fitch (1958:270) found the
territories of several pairs of Bell Vireos at the University of
Kansas Natural History Reservation to vary from 0.4 to 1 acre. Hensley
(1950:243) estimated the size of the territory of a pair of Bell
Vireos observed in Piatt County, Illinois, at 3.1 acres. Nolan
(1960:227) records home ranges of 2 to 3 acres. The pairs that he
studied were sole occupants of fields several acres larger than the
portions actually utilized. His description of the vegetation
indicates that most of the second growth was not much taller than 7
feet. As indicated elsewhere, the second-growth in my tract averaged
15 feet tall. The smaller average size of territory (1.25 acres) that
I found is probably a function both of this greater vertical range of
available foraging area and the much higher gross density of birds (40
pairs per 100 acres).

_Permanence of Territories_

Most pairs remain in their original territories throughout the summer,
although some shift certain territorial boundaries. In 1960 pairs 2
and 6, in the course of selecting a site for a replacement nest,
annexed adjacent areas previously occupied by other pairs. Pair 2
relocated in a space that originally included territories 1 and 4, and
pair 6 built a nest in an area formerly occupied by pair 7. Males 1
and 4 were sacrificed for specimens and pair 7 probably was destroyed
by a predator. Owing to the presence of a nest, the annexed area
becomes the focal point of the activities of a pair, but the original
area is regularly visited and may be returned to in a later renesting.

TABLE 2. SIZE OF THE NINE ORIGINAL TERRITORIES OCCUPIED IN 1960.

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| Date first |
Territory | occupi