Table 1. Numbers and Distribution of Captures and Recaptures of Blue
Racers on the Reservation and Rockefeller Tract
=======================+=========================+=======================
Span of years within | Number of separate | Number of times
which each individual | years within which each | each individual
was captured | individual was captured | was captured
---------+-------------+-----------+-------------+----------+------------
| | | | Times |
Years | Individuals | Years | Individuals | captured | Individuals
---------+-------------+-----------+-------------+----------+------------
1 | 749 | 1 | 749 | 1 | 679
2 | 137 | 2 | 197 | 2 | 181
3 | 56 | 3 | 51 | 3 | 93
4 | 32 | 4 | 15 | 4 | 31
5 | 19 | 5 | 6 | 5 | 7
6 | 13 | 6 | 1 | 6 | 14
7 | 7 | 7 | 0 | 7 | 8
8 | 2 | 8 | 1 | 8 | 4
9 | 3 | | | 9 | 1
10 | 0 | | | 10 | 0
11 | 1 | | | 11 | 0
12 | 1 | | | 12 | 1
| | | | 13 | 0
| | | | 14 | 0
| | | | 15 | 0
| | | | 16 | 1
---------+-------------+-----------+-------------+----------+------------
This investigation was based primarily on the capture in live-traps,
marking, release, and recapture of blue racers in their natural
habitat. On the combined area of the Reservation and the Rockefeller
Experimental Tract, 1020 blue racers were recorded a total of 1688
times from August 30, 1948, to October 27, 1962. At Harvey County Park
361 blue racers were marked, and were captured a total of 467 times
from May 6, 1959, to September 14, 1962, and at Cedar Bluff Reservoir
42 were captured from May 11, 1959, to June 30, 1960.
The traps used were cylinders of galvanized wire, "hardware cloth"
(Fitch, 1951:77; 1960:77), having funnels opening into each end, or
having a funnel at one end and a plug at the other. The traps, open at
both ends, were used along hilltop rock ledges where an exposed
vertical rock face provided a barrier along which a snake might travel
and where it could be easily intercepted by the trap without any
accessory equipment (see Pl. 21, Fig. 1). Where such natural barriers
were lacking, as in level fields, barriers consisting of boards,
screens or sheet metal were installed to guide the racer toward the
trap and into a funnel entrance. Two such barriers at each end of a
trap forming a V to guide the snake into the funnel were used in 1956
and 1957, when trapping at places away from the hibernation ledges was
undertaken. Later it was found simpler and more effective to use a
single barrier with a trap at each end. The barrier extended up into
the funnel entrance, and usually the racer, following along the
barrier on either side, would pass into the funnel and through its
apex. However, it was possible for a racer to travel around the end of
the barrier without entering the trap, and perhaps some did so.
The need for making the barrier and trap a tight unit impassable to
the snake, was somewhat counterbalanced by the need for having the
whole installation loosely constructed so that it could be easily
altered, opened, adjusted, and cleaned. Since the traps were kept set
in large numbers, and the task of checking them was time-consuming,
speed of operation was more important than the perfect functioning of
any one trap. Approximately 200 traps were kept set when operations
were at their maximum. No record was kept of the number of "trap days"
involved in the study, but the total was well over 100,000 for the
Reservation and the Rockefeller Tract. When traps were set at both
ends of a barrier, the outer end of each trap was closed with a plug.
No bait was used in the traps. Occasionally small vertebrates and
insects of kinds used as food by the racers may have gotten caught
first and served to attract the snakes. Best catches of racers were
made in the breeding season, since males were attracted by females
already in the traps, and several males might be captured
simultaneously with one female. Occasionally as a person approached or
handled a trap, a racer darted out of it, displaying a perception,
acuity of vision, and skill in avoiding the inward projecting wire
prongs encircling the small funnel opening, that were exceptional
among the several species of snakes trapped. Doubtless many other
racers that were caught in traps escaped before they were discovered.
If the funnel entrance of the trap was of the same diameter as the
snake itself, or only a little larger, there was little likelihood of
the trapped racer escaping. However, funnel openings were usually
adjusted at a diameter of approximately 1-1/4 inches, allowing an
ample margin for even the largest racers, though inadequately small to
permit ingress of a few of the largest black rat snakes, bull snakes
and timber rattlers occurring locally.
Ordinarily the snakes trapped were processed in the field and released
immediately. The method of marking was essentially that of Blanchard
and Finster (1933:334). Two subcaudals, one on the right side and one
on the left, were clipped on each snake, and when these marks healed
they left permanent scars. In the racer, as in most other colubrines,
the subcaudals are divided into a double series, one on the left and
one on the right. Scales of the left and right sides are placed
alternately. At the base of the tail one or more undersized scales
usually are present on each side, and there might be some question as
to precisely where the count should begin. The rule followed was to
exclude from the count any small basal scales on either side that did
not extend medially to contact at least one scale of the opposite
side. The scale designated as "one left" (or "one right") was the
first to contact one of the opposite series, regardless of whether the
former was of normal size or (as was usually the case) smaller and
narrower than those following it. In marking, this "number one" scale
was never clipped but was left as a point of reference since a base
mark was needed from which to begin the count. The marks were read
from left to right, for example U 5_l_ 2_r_, the "U" referring to the
subcaudals or "urosteges," the "5_l_" indicating the fifth on the left
side, and "2_r_" indicating the second on the right. The subcaudals
clipped were the first 19 following the basal scale. When the 361
possible combinations all had been used, ending with U 20_l_ 20_r_, a
new series was begun duplicating the first except that on each snake
the first ventral (or "gastrostege") anterior to the anal plate was
clipped on the left side (G1L) to distinguish these snakes from the
series previously marked. Later, a third series, "G2R" was marked,
and eventually a fourth series, "G3L" was started.
There were many borderline instances in which the basal scale barely
contacted one of the opposite side. In such instances the formula was
written U 5_l__{ISB} 2_r_, the subscript ISB signifying "including
small basal." In other instances a basal subcaudal barely failed to
contact a scale of the opposite side and this condition was indicated
by the subscript NSB--"not including small basal." The condition might
be so nearly equivocal that on successive occasions the same formula
might be read U 5_l__{ISB} 2_r_ and U 4_l__{NSB} 2_r_. Occasional
misidentifications of individuals that resulted from such
discrepancies were in most instances readily detected when the field
records were transferred to individual file cards where the sex, size,
and location of the snake at its previous captures were shown.
In some instances racers recaptured after periods of years retained
conspicuous scars where scales had been clipped, but in other
instances the marks had become obscure, and in fact the only trace of
a mark might be a slight narrowing or notching of part of the scale
originally clipped. Snakes caught and marked early in life probably
retained more power of regeneration than those clipped after the
attainment of maturity, but otherwise the basis for difference in
extent of regeneration was not evident. In the same snake, three
scales, all clipped on the same day, might show much different degrees
of regeneration after the lapse of a year or more. In general,
obscuring of marks by regeneration was a source of inconvenience
rather than of error; only a negligible percentage of the recaptured
racers had marks so obscure that their identities might have been
seriously questioned, and it is doubtful that any marks were lost
completely by regeneration.
Racers found in traps were removed, measured (snout-to-vent length,
tail length), weighed in a cloth bag suspended from spring scales, and
marked. The mouth was forced open and the snake was examined for
flukes. Enamel paint of a bright color, red, green, yellow, blue or
orange was smeared on the snake to gain information regarding the time
of molt. The stomach was palpated for recently ingested food items,
and any detected were forced up into the gullet to be identified, then
were squeezed back into the stomach. The rear part of the body was
palpated to detect undigested material in the gut, and if any was
present, an attempt was made to squeeze out the fecal material, using
only light pressure, with care not to injure the racer. The inside of
the trap and the ground beneath it were inspected for fecal material
that might have been voided while the snake was confined. Any
scatological material obtained was wrapped in a paper towel, labelled
and brought back to the laboratory where it was stored. Eventually
each scat was soaked for a day or more in a detergent solution, rinsed
in running water in a fine gauze bag, dried, and placed with its label
in a cellophane envelope for subsequent microscopical study.
Various items concerning reproductive condition were also routinely
recorded. In females the ventral surface was palpated at the rear end
of the body to detect the genital bursa or vagina, which in sexually
mature individuals has a much thickened wall, and can be felt as a
distinct lump. Males were likewise tested for sexual maturity by
pipetting a small amount of fluid from the cloaca into a vial and
returning it to the laboratory where it was examined microscopically
for motile sperm. Also, sperm samples were often taken from males at
different times throughout the season of activity, and cloacal samples
from females occasionally were checked for sperm as evidence of recent
copulation.
In the summer of 1962 an outdoor enclosure of 100-foot circumference
was constructed, of galvanized sheet iron, with wall three feet high,
set on a concrete base extending to a depth of two feet. A
two-foot-deep concrete basin inside the enclosure served as a water
container. The enclosure was partly shaded by a large walnut tree and
the area enclosed had lush vegetation, including brome grass, various
shrubs, and young trees up to 15 feet high, thus including most
features of the racers' habitat, and it was situated in an area
frequented by the snakes. Throughout the summer several racers were
kept in the enclosure, and frequent observations on them yielded much
information concerning time of activity, temperature preferences, and
social and sexual behavior that could not have been obtained readily
either from racers confined in small cages or from those free under
natural conditions.