Blue racers that were recorded on more than one occasion were rarely
caught again at the original location. For different individuals,
distances between capture points ranged from zero up to a little more
than three-fourths of a mile. The area of concentrated study was a
mile and a half in greatest diameter; there was scant opportunity for
capturing racers that moved greater distances. Even those that moved
as far as a mile would have passed beyond the boundaries of the study
area in most instances. Many of the marked racers that disappeared
from my records probably moved beyond the limits of the study area.
Nevertheless, in the great majority of instances, the distances
between successive capture points for the same individual were
relatively short, indicating that each racer tends to remain
permanently in a restricted area.
Most captures were made in the type of grassland or brush that
provides favorable habitat for the racer during the season of
activity, but many other captures were made in woodland along the
rock ledges where the snakes come to hibernate. Four different types
of movement may be recognized: 1) those in the rock ledge area where
hibernation occurs; 2) those between the area where the summer is
spent and the hibernation ledge--an actual small scale seasonal
migration which takes place in spring and autumn--3) those within a
home range, which are part of the day-to-day activities of the racer,
and, 4) wandering movements by which the racer shifts its activities,
perhaps permanently, from one area to another. In the records of any
one snake these different types of movements cannot always be sorted
with certainty. Each type will be discussed separately.
Relatively few movements along the ledges were recorded. It seems that
having migrated to a ledge, the racer promptly finds its hibernaculum
and retires for the winter. In spring there is equally prompt
scattering of the emerging racers, which no longer find the ledge
attractive. Most recorded movements along the ledges were short. Of 76
movements, nine exceeded 1000 feet, and only four others exceeded 500
feet. Most of the shorter movements were recorded within an autumn
season, but several were recorded after the lapse of one or more
seasons of activity. The longer movements were as follows: 1250 feet
after 8 seasons (male); 1300 feet after three seasons (female); 1600
feet after one season (female); 2000 feet after one season (female);
2280 feet after seven seasons (male); 2200 feet in same season
(female); 2410, 2600, and 3200 feet, each after one season (all
males). The trend of these records suggests that the tendency to
return year after year to the same hibernaculum is not strong; after
using one for a period of years, the racer may abandon the stretch of
ledge and, starting out in the opposite direction from its summer
range, find a new hibernaculum as much as half a mile from the old
one. Records of distances between capture points on the ledges for
individual racers are shown in Fig. 12.
A total of 124 movements between summer ranges and ledges were
recorded, and the distances averaged 1309 feet--approximately a
quarter mile. Some racers living in hilltop fields may have had home
ranges that included rock ledges, or at least were adjacent to them.
In such instances no seasonal migrations would have been necessary to
reach hibernacula in the autumn and summer ranges in the spring.
Several short movements--100 feet, 150 feet, and 200 feet--can be
explained on the basis that home ranges and hibernation ledges
overlapped or were near at hand, but most of the movements were
longer. The longest movement was 4020 feet, after a lapse of four
seasons. Twenty-four movements exceeding 2000 feet were recorded. For
these the intervals between captures averaged more than double the
time for the remaining movements, indicating that the longtime
permanent shifts were involved in many instances.
[Illustration: Fig. 9. Histogram of movements of blue racers between
hilltop rock outcrops used for hibernation, and summer habitat on the
Reservation and Rockefeller Tract. Movements of females tend to be
somewhat shorter than those of males.]
For all the racers living in bottomland, ranges were separated from
ledges by areas of wooded hillsides averaging approximately 700 feet
across. These relatively unfavorable areas had to be traversed in the
course of the semi-annual migrations. Even some of the racers that
lived in hilltop fields apparently crossed wooded slopes in order to
reach distant hibernation ledges, or else each reached the ledge by a
roundabout route although it could have found a ledge much nearer its
summer range. For the 124 ledge-to-field and field-to-ledge movements,
the median distance was 1030 feet. The sexes were almost equally
represented in this sample but the average distance for the 55
males--1425 feet--notably exceeded that for the 69 females--1220 feet.
These movements are shown in Fig. 9.
McCauley (1945:76) in Maryland described what seemed to be incipient
territoriality in a large male racer that remained several hours in a
small area, crawling about conspicuously with head raised, seemingly
on patrol. When an even larger male racer intruded, the first one
aggressively drove him away, but neither paid any attention to a king
snake that was also on the area. Other authors have noted the
attachment of a racer to a small familiar area. Conant (1938:53) wrote
that many of the racers he saw sought shelter in definite retreats.
One of these racers was seen resting on top of a brush pile four times
in a single afternoon, and each time it followed the same route to the
same inaccessible spot beneath the brush.
My own observations do not bear out the idea that racers maintain
regular territories, since several males may be present within a small
area, even in the breeding season. Hostile behavior between males has
not been observed by me under natural conditions, and in confinement
has been seen only in instances of self defense. Like the racer Conant
observed on a brush pile, individuals may linger in the vicinity of a
favored shelter or foraging area for periods of hours, but such
associations are ephemeral, and soon the snake moves on. In a
uniformly favorable habitat a racer may cruise about freely in tall
grass or brush. Individuals that I have attempted to follow, after
flushing them or releasing them from traps, often covered distances of
100 to 300 feet within periods of a few minutes before I lost them. In
such instances I maintained sufficient distance between myself and the
snake so that the latter was not actively escaping. Probably the snake
was not aware of pursuit in most instances, although I was able to
glimpse it through the stems of grass, weeds, or shrubs, or was
informed of its course by the swaying tops of grass and other
vegetation.
For many of the racers captured over periods of years it was possible
to plot "minimum home ranges" in the areas that they occupied. One
caught 12 times in five consecutive years will serve as a typical
example. There were seven locations involved; three captures were made
at one point and two captures at each of two others; the other five
locations were each represented by a single capture. One of the seven
locations was for a capture made at a rock ledge in October, and hence
can be eliminated from considerations of home range. The other six
locations are based upon captures made from late May to early August,
and they form a rhomboid pattern, with three locations in alignment on
one side and two others inside the quadrangular figure formed by the
five outlying points. Obviously such a group of records gives some
idea of the location and extent of the snake's activities but the
information is far from complete. As shown by Odum and Kuenzler
(1955), a much larger series of records, usually several dozen, with
eight or more marginal locations, is necessary to illustrate even an
approximation of the actual home range. Under the conditions of my
study such a series of records was unattainable. Few if any of the
racers recaptured had more complete series of records than the one
mentioned above.
For 20 racers the records were sufficiently numerous and well
distributed to permit plotting of minimum home ranges. One of these
ranges was hexagonal, nine were pentagonal, eight were rhomboidal and
three were triangles. In four instances the area encompassed was
broken by woodland, indicating that the home range comprised two or
three disjunct segments. In all instances the smaller segments were
triangular. The 20 minimum home ranges averaged 6.6 acres (3.2 to
12.8). The 15 ranges of males averaged 7.3 acres, whereas the five
ranges of females averaged only 4.5 acres, but the sample is too small
to be relied upon for differences in the sexes.
[Illustration: Fig. 10. Movements of blue racers within or between
areas of summer habitat on the Reservation and Rockefeller Tract. The
trends are much alike for males and females.]
In an earlier publication (Fitch, 1958:73) I discussed an alternative
method for determining size of home range in animals that move about
freely within a chosen area, not having their movements restricted by
attachment to a specific home base. Ordinarily any two records of the
animal within its home range will be separated _on the average_ by a
distance equal to half the diameter of the area. Assuming that home
ranges in general tend to have a circular shape, except as restricted
by limiting environmental factors, the area can be easily computed
from the average recorded movement--the home range radius. It is
necessary, of course, to have a sufficiently large number of records
of movements to obtain an average that is statistically reliable.
A major problem is that of recognizing movements that involve an
extension of the original range or a shift away from it to a new area.
A few exceptionally long movements were recorded. If these are
included in the computations of home range, they greatly increase the
average distance, probably introducing error. Also, the number of
exceptionally short movements was greater than might have been
expected if all locations of capture are at random to each other. In
some instances a racer newly released may have blundered into the same
trap again, or into the trap at the opposite end of its drift fence.
In other instances traps may have been so strategically situated with
respect to preferred travel routes that they caught the same snakes
repeatedly. In still other instances, the range of an individual might
have been mostly outside the study area, with only one end or corner
overlapping the trap sites.
A total of 471 records for consecutive captures in field areas is
available, 305 for males and 166 for females. In 20 instances
successive sites of capture were the same and movement was recorded as
zero. Of the 471 records, 207 involved a relatively long time span,
including at least one hibernation period; the remaining 264 were
based upon successive records within the same season of activity. The
trends were much the same in the records involving a longer time span
(up to four years) as in those records involving captures made in a
single season, but for the longer periods there were some
exceptionally long movements, and relatively few short movements of
less than 100 feet.
Records of male racers and those of females were used for separate
computations. For each series, the ten per cent of movements that were
longest and the ten per cent that were shortest were eliminated from
consideration in calculation of the average distance between points of
capture. For the remaining 244 records of males an average movement of
595 feet was calculated, and for 132 records of females an average
movement of 574 feet. These distances, if accepted as typical home
range radii, would represent home ranges of 26.3 acres for males and
23.8 for females. In an earlier discussion of spatial relationships in
the racer (Fitch, 1958:119), based upon relatively scanty data, I
estimated the home range to be approximately 23 acres in males. But
with only nine records for female racers I calculated the home range
to be 9.7 acres.
The disparate figures obtained from plotting minimum home range and
from calculating average home range radius are not irreconcilable,
since a minimum home range based on only four or five points would
ordinarily include only a fraction of the actual range. Distances up
to 1500 feet are included in the calculation of home range. It seems
that home ranges often have a diameter of this magnitude or a little
larger, although the estimated average diameter is 1140 feet. Home
ranges probably most often deviate from circular shape to form an
ellipse, with one diameter markedly exceeding the other. Woodland,
water, roads, buildings, or cultivated fields, or other areas that are
unfavorable or uninhabitable often form the boundary of a home range
and influence its shape.
Many of the longer movements constituted clear-cut shifts in range. In
one exceptional instance a large adult female captured in the
northeastern part of the Reservation on June 22, 1950, was released 21
days later at a point 3900 feet southwest of the place of capture. On
May 27, 1960 she was caught within 600 feet of the original location,
seemingly having made a homing movement. Among the nine racers
recorded to have made longest movements (exclusive of those movements
made to or from hibernacula) four were recorded also to have made
later long movements in the reverse direction, probably returning,
each to its original home range, although in every instance the return
movement was somewhat less than the original. A female of two-year-old
size when first captured on September 2, 1957, was recaptured 3100
feet southeast on May 10, 1958. On August 7, 1959, she was recaptured
again 2400 feet from the second location in the direction of the
original capture. Similarly, in a three-year-old female a shift of
2730 feet was recorded at the second capture after 21 months, and at
the third capture 14 months after the second, a return trip of 2360
feet had been made. A second-year female made a trip of 2640 feet
between May 17 and October 1, 1960; by May 1961 she had returned 2000
feet to the vicinity of her original capture. From one year to the
next an adult male shifted 2450 feet; after another year he had moved
back 1550 feet. Most of the longer movements recorded were those
between home ranges in fields and hibernacula along ledges, but in
this class of movements, distance was somewhat proportional to elapsed
time. For 59 such movements exceeding 2000 feet the average was 3.1
years, whereas for 114 field-to-ledge movements of less than 2000
feet, average elapsed time was 1.6 years. This trend suggests that
over periods of years a racer is likely to shift its range or its
hibernaculum or both.
[Illustration: Fig. 11. Map showing home ranges of five blue racers,
as indicated by numerous captures in successive summers, in small
valley where Reservation headquarters are located, and spatial
relations of their hibernacula, as represented by points of capture
along hilltop limestone outcrops. In spring and autumn, traveling to
and from hibernacula, the snakes migrate across wooded slopes. Each
"minimum home range" is enclosed in a dotted line, and a distinctive
symbol is used to show successive points of capture for each snake.]
[Illustration: Fig. 12. Map of 600-acre area of Reservation and
Rockefeller Tract, including parts where field study was most
concentrated, showing movements of the 20 blue racers recorded to have
shifted over the longest distances. The figure following the sex sign
of each individual indicates number of months elapsed between the
captures at the localities represented by the dots.]
Average elapsed time between captures was 7.7 months. In the 471
field-to-field movements recorded, 53--slightly more than eleven per
cent--exceeded 1500 feet and can reasonably be considered shifts of
home range. The average elapsed time between captures for this group
of snakes was 9.5 months. The evidence suggests that, even in an area
of favorable habitat, somewhat more than ten per cent of the racers in
a population annually shift their home ranges somewhat, but that many
stay in the same home range for periods of years or perhaps throughout
life.
Shifts in range were especially noticeable where availability of
suitable habitat underwent seasonal change. Along the north edge of
the Reservation, prairie adjoined cultivated fields where grain or hay
was grown. Until late May, the cultivated crops made little growth and
the fields were almost bare. They provided insufficient shelter for
the racers, which tended to keep to the prairie, where old grass of
the previous year's growth furnished them with ample cover. Later in
the season, crops, of oats, wheat, and alfalfa constituted suitable
cover for the racers, and many of them shifted their ranges to the
cultivated fields, but corn and milo crops were much less adequate for
their needs. After harvesting of crops, cover in the fields was again
inadequate for the racers' needs, and they tended to retreat to edge
situations, or to adjacent prairie.