certain segments of the study area and by the
individual variation in the song of the males. Sexes were
distinguishable on the basis of differences in vocalizations and
plumages.

Most nests were located by the observer searching, watching a pair
engaged in building, or following a singing male until the increased
tempo of his song indicated proximity to a nest. As the season
progressed and the foliage grew more dense, it became increasingly
difficult to locate completed nests. Blinds were unnecessary because
of the density of vegetation. Observations were facilitated by a 7 x
50 binocular. Data were recorded on the spot in a field notebook. Eggs
were numbered by means of Higgins Engrossing ink as they were laid.

Individual trees in which males sang most were marked over a
three-week period. Then the distances between the most remote perches
were paced. These distances aided in determining the size of the
territories. The general configuration of the vegetation within each
territory determined the location of one or more boundaries of the
territory. Each territory was given a number, 1, 2, 3, etc., as it was
discovered; consequently there is no numerical relationship between
the designations of the territories established in 1959 and 1960.
Nests within a territory were designated as 1-a, 1-b, 1-c, etc.

Although experimentation was not a primary source of data, it proved
useful in certain instances. A stuffed Blue Jay elicited mobbing
behavior from nesting pairs. A dummy Bell Vireo elicited both
agonistic and epigamic behavior from nesting pairs, depending on the
phase of the nesting cycle.

The temperature at the beginning of each day's work was taken by means
of a Weston dial thermometer. A hand counter and a pocket watch having
a second hand were used in determining such data as frequency of song
and periods of attentiveness by the sexes. Histological
cross-sections, prepared by A. Wayne Wiens, of the ventral epidermis
of both sexes were used to study brood patches.

STUDY AREA

The intensive field work was on a 39-acre tract (fig. 1) extending
approximately 7/10 of a mile west from U. S. highway 59, which in
1959-1960 constituted the western city limit of Lawrence, Douglas
County, Kansas. The eastern boundary of the study area is
approximately 1-1/2 miles southwest of the County Courthouse in
Lawrence. The eastern ten acres is associated with the Laboratory of
Aquatic Biology of the University of K