HARVARD UNIVERSITY
Library of the
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UBRARy
N0V~6 Hflr
OCCASIONAL PAPERS
ofthe U&B&*°
MUSEUM OF NATURAL HISTORY
The University of Kansas
Lawrence, Kansas
NUMBER 118, PAGES 1-11 17 OCTOBER 1985
OBSERVATIONS ON RATTLE SIZE AND
DEMOGRAPHY OF PRAIRIE RATTLESNAKES
(CROTALUS VIRIDIS) AND TIMBER RATTLESNAKES
(CROTALUS HORRIDUS) IN KANSAS
By
Henry S. Fitch1
INTRODUCTION
Detailed life history studies have made possible interspecific com-
parisons of demographic parameters such as reproductive potential, age-
specific mortality, and survivorship. These data are usually obtained from
recaptures of marked individuals. However, these same parameters may
be investigated from direct observation of population samples.
Here I provide demographic comparisons of two species of rat-
tlesnakes, the prairie rattlesnake (Crotalus viridis) and the timber rat-
tlesnake (Crotalus horridus). Few mark-recapture studies of rattlesnakes
have been undertaken, but these snakes are unusual in carrying a record of
individual growth and shedding, the rattle, consisting of accumulated
successive sloughs from the tail tip. The correlation between size, age, and
rattle number facilitates analysis of population composition through
allocation of individuals to their annual cohorts.
As clarified by Klauber (1956) and other authors, each rattlesnake is
born with the tail ending in an epidermal, keratinous tip, the "prebutton."
Within a few days after birth the young snake sheds its skin, and the
expanded knobby base of the corneous tail tip is then exposed, the whole
structure being the snake's first rattle segment, the "button.' ' At each
subsequent shedding a new rattle segment appears, as each is actually shed
skin from the terminal portion ofthe tail tip, designed by its shape to cling
to the tail base. A typical rattle segment consists of three lobes, anterior,
middle, and posterior, separated by deep transverse grooves. Except on
the terminal rattle segment, only the anterior (proximal) lobe of each
1 Museum of Natural History and Department of Systematics and Ecology, The
University of Kansas, Lawrence, Kansas 66045 U.S.A.
2 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY
segment is exposed to view, as the second and third lobes fit inside the next
posterior (more distal) segments and provide bases of attachment. As the
snake ages and sheds, its rattle lengthens; the button and other terminal
segments eventually are lost. Because each rattle segment has posteriorly
tapering lobes, the rattle string may taper to the rear even if the snake is an
older one that has lost its button and early rattles acquired during its first
few years of active growth. There is widespread misunderstanding of this
sequence and most lay observers do not distinguish between intact rattle
strings ending with the original button and incomplete strings that lack the
button and other early rattles lost through wear or accident. However, the
button is of relatively small basal diameter, is rounded, and is loosely
attached, whereas in a rattle lacking a button the terminal segment is a
single rigid structure consisting of 2-4 (usually 3) successive lobes which
are angular, relatively wide across the base of the anterior lobe, and have
ridges and points on the posterior lobe.
METHODS AND MATERIALS
A sample of prairie rattlesnakes was obtained from the Cimarron
National Grassland and adjacent private land in Morton County in the
southwestern corner of Kansas; 25 snakes were captured, processed alive
and released on 26 April and 1 and 2 May 1984; 45 others were collected
by Steve Barnum of Straight, Oklahoma, and were similarly processed on
2 May 1984. Rattles, 84 in all, saved as trophies by Gary Norton of
Hugoton, Kansas, and Ed Anderson of Elkhart, Kansas, were obtained as
the snakes emerged from hibernation in the spring of 1983 and previous
years, and were used to supplement the demographic data from the live
snakes. Also, 38 preserved specimens of C. viridis in the Museum of the
High Plains, Fort Hays State University, and 24 in the University of
Kansas Museum of Natural History were examined. These museum
specimens, shrunken to varying degrees in preservative, were used only
for study of rattle strings and of reproduction.
The sample of timber rattlesnakes included 93 individuals captured
from October 1948 to May 1984 on the University of Kansas Natural
History Reservation and adjacent areas, 26 captured near DeSoto, Johnson
County, in May 1983 and 1984, and five from near Clinton Reservoir,
Douglas County, in May 1984. Most of these snakes (a total of 100,
excluding 24 summer records), were captured in spring (April, May) or
fall (late September, October) and hence represented the period between
growing seasons and could be grouped in discrete annual cohorts. The
youngest group consisted of those born in the preceding late summer and
early fall, with no rattles other than the natal button.
The rattle of each snake was examined and the separate segments were
counted and measured in order to correlate their size and number with the
age, size and sex of the snake. Presence of the natal button was noted or, if
the rattle string was incomplete, estimate of the number of missing
segments was attempted. Three classes of rattle strings could be distin-
guished:
DEMOGRAPHY OF KANSAS RATTLESNAKES 3
Type I: tapered terminally, and complete, including the postnatal
button.
Type II: with noticeable taper, but incomplete, lacking the terminal
button and perhaps other segments.
Type III: incomplete, non-tapered, having only segments of large and
relatively uniform size.
Incomplete rattles that are tapered indicate that few segments are
missing, whereas those that are non-tapered show that all segments
acquired while the snake was growing, and perhaps others produced
subsequently, have been lost. "First-year" snakes in this account are those
less than one year old; "second-year" are those between one and two
years, and "third-year" are those between two and three. Diameter of
each rattle segment was measured with calipers to the nearest tenth of a
millimeter, the greater (dorso-ventral) diameter or height (termed
"width" by Klauber, 1956) of the proximal (anterior) lobe of each
segment.
The samples of C. viridis (Table 2) and C. horridus (Table 3) were
divided into tentative age groups on the basis of rattle number. Neonates
comprised a discrete and easily recognizable class in the fall-spring
samples, and second- and third-year young also were fairly separable both
from the neonates and from adults. The adults were assigned arbitrarily to
most probable age classes on the basis of rattle number. Those of C. viridis
were assumed to add rattles at an average rate of approximately 1.5 per
year. This figure seems plausible in view of the findings that one shedding
per year is normal for C. v. oreganus in the relatively short growing
season of northern Idaho (Diller and Wallace, 1984) and between one and
two sheddings in California (Fitch, 1949). Two sheddings per year have
been found in C. horridus in Shenandoah National Park (W. H. Martin III,
pers. comm.) and that is supported in my study by the recapture of an adult
male marked 2 June 1953, which had added 4 rattles by 16 October 1954.
RESULTS
Prairie rattlesnake. Evidence from the relative size of successive
rattle segments indicated that in C. viridis (and also in C. horridus) most
growth takes place between the first four sheddings, and that increase in
diameter of successive segments is relatively slight (less than 5%) after the
seventh ecdysis (Table 1). Type II rattles usually have one to four
segments missing (including the button), and are from relatively young
snakes. The oldest individuals in the population have a Type III rattle of
several or many segments, all of about the same diameter, because they
were acquired after the snake had completed its growth or had slowed to a
negligible rate of gain.
The population from Morton County, Kansas, bore out Klauber's
(1956) statement that immature Crotalus v. viridis in den collections were
concentrated in the one-rattle and five-rattle classes, representing first- and
second-year age classes (Table 2). When only the button or two or three
terminal segments were missing and the rattle string had a distinct taper
OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY
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DEMOGRAPHY OF KANSAS RATTLESNAKES 5
(Type II), it was possible to account for the missing segments easily with
little margin of error. In a few of the largest snakes having almost
uniformly wide rattle segments (Type III) the allocations are speculative.
In such instances, the minimum possible ages and segment counts were
used, and I assumed the snake must have lived at least four years and
produced at least eight rattle segments before it began to produce those of
maximum size. Thirty of the 70 snakes (43%) and 36 of the 84 rattle
strings (43%) had one or more distal segments missing, and so were Type
II or Type III rattles.
Klauber's (1956) discussion of the frequency of shedding and rattle
gain in C. v. viridis was based upon abundant material from dens near
Platteville, north-central Colorado. He stated that in these hibernating
aggregations there were many young of the year (with only the button) but
there were few young with two or four rattles, almost none with three, and
many with five. The latter group thus represented the mode for one-year-
olds. Klauber (1956) and Heyrend and Call (1951) noted that first- and
second-year young were not well represented in denning aggregations in
Colorado and Utah. In my Morton County sample also, such young are
relatively few. However, in a normal population, there must be more one-
year-olds than two-year-olds, and more first-year young than one-year-
olds.
Klauber (1956) also noted geographic variation in rate of rattle gain;
one-year-old C. v. helleri in San Diego County, southern California, and
C. v. oreganus in Madera County, central California (Fitch, 1949),
typically have four rattles but C. v. lutosus in northwestern Utah most
often has three (sometimes four) according to Heyrend and Call ( 195 1 ). C.
v. viridis of southwestern Kansas is similar to those of Platteville,
Colorado, but different from more western populations of the species
having a more rapid rate of rattle gain. The modes for first-year and
second-year cohorts are, respectively, 1 rattle and 5 rattles, and for the
third-year cohort, 8 rattles (but with 7 almost as often).
Births of Crotalus viridis are concentrated in August and September,
hence the youngest, or " first-year' ' snakes in the spring sample (late April
and early May) from Morton County, Kansas, were about eight months
old, but they had been in hibernation most of the time since birth the
previous autumn, and therefore probably had grown little. The next cohort
consisted of those about 20 months old with successive annual groups
about 32, 44, 56 and 68 months old (Table 2).
Snakes with seven-, eight-, nine-, and ten-segmented rattles comprised
the majority of adults and 45% of the total sample (Table 2). Those having
seven- and eight-segmented strings must be predominantly in their third
year and newly matured. Evidently at adolescence there is an abrupt
slowing in both growth rate and shedding frequency, so that snakes of the
third-, fourth-, and fifth-year age classes overlap widely in both snout-vent
length and number of rattle segments.
The incidence of mortality in adults is suggested by the rapidly
decreasing numbers of older snakes as indicated in Table 2; third-year,
fourth- and fifth-year, and sixth- and seventh-year classes had respec-
5 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY
Table 2. Prairie rattlesnakes (Crotalus viridis) of a spring sample (70
live snakes, 84 detached rattles) from Morton County, Kansas, divided
into tentative age cohorts on the basis of size (SVL) and rattle
segments.
Tentative
age cohort
Number of
rattle
segments1
N
Percentage
of sample
ratio2 Snout-vent length in mm
First-year
immatures
1 (button
only)
2(1+B)
23
3
14.9
2.0
6-7 334 (291-360) in 13
Second-year
adolescents
3 (2 + B)
4 (3 + B)
5 (4 + B)
6 (5 + B)
11
9
0.6
5.2
7.1
5.8
1-2 557 (520-620) in 3
7-2 670(636-710) in 9
733 (708-820) in 4
Third-year
adults
7 (6 + B)
8 (7 + B)
14
24
9.1
15.6
3-4
6-7
863 (760-890) in 7
846 (723-905) in 13
Fourth-year
adults
9 (8 + B)
15
9.8
3-3
890 (830-930) in 6
Fourth- and
fifth-year
adults
10 (9 + B)
15
9.8
2-2
932 (646-1020) in 4
Fifth-year
adults
11 (10 + B)
14
9.1
3-3
934 (880-1038) in 6
Sixth-year
adults
12 (11+B)
9
5.2
3-0
947 (900-1000) in 3
Sixth- and
seventh-year
adults
13 (12 + B)
5
3.3
0-1
950
Seventh-year
adult
14 (13 + B)
1
0.6
1-0
978
Eighth-year
adults
15 (14 + B)
16 C15 + B)
1
1
0.6
0.6
1 Many of longer rattles reconstructed from incomplete strings: figures somewhat speculative
for certain strings of more than 10 segments.
2 Live snakes only (exclusive of detached rattle strings).
tively, 38, 44, and 6 individuals, with only 2 that were judged to be older
than seven years. However, the allocations in age classes are somewhat
speculative, as beyond the third year age cohorts overlap in both size and
number of rattle segments.
Among the 20 sexually mature female prairie rattlesnakes that were
palpated, 14 (70%) had enlarged ova that could be counted, whereas six
had no detectable ova and presumably were not going to produce young
during the 1984 season. Similarly, in New Mexico, Aldridge (1979) found
73% of 44 females of C. v. viridis to be fecund. In the northern Great
Plains there is a well-defined biennial cycle (Rahn, 1942). One Kansas
female dissected on 26 April had enlarged follicles (18 x 9mm), and
follicles in those palpated seemed to be about this size or larger. Egg
complements counted by palpating were 5, 6, 7, 8, 8, 9, 10, 10, 11, 11, 12
DEMOGRAPHY OF KANSAS RATTLESNAKES 7
and 18 follicles, mean 9.7. In museum specimens females had egg
complements of 6, 7, 9 and 16. Marr (1944) mentioned two Kansas litters
of 14 each. For the combined sample of 19 Kansas litters, mean clutch size
was 10. 1 1 ±0.79, which is within the known range for the species and for
the subspecies C. v. viridis.
Stillborn young and abortive infertile eggs are common in rattlesnake
litters. Klauber (1956) stated that in 28 broods (of various species) at the
San Diego Zoo, there were 274 eggs or young, with 70% live young, 12%
dead young, and 18% infertile eggs. For C. viridis under more natural
conditions, in northern Idaho, Diller and Wallace (1984) found that 24 of
197 ova failed to develop because of infertility or fetal death, a loss of
12.2%. If this figure applies in C. v. viridis populations of Kansas, the
mean of 10. 1 eggs ovulated would produce a litter of 8.9 live young. In the
combined sample (rattles and live snakes) 104 of 154 were considered
adults (third year or older) with an estimated 52 females. If 70% of them
were fecund, with an average litter of 8.9, the annual crop would total 324
young.
The mortality rate in first-year young would be expected to exceed that
in older age groups. However, the relatively rapid and progressive decline
in older snakes (recognizable by large size and numerous rattle segments)
suggests that adults of all ages also are subject to high rates of mortality.
Various mortality rates were empirically tested against the figures at hand
for estimated ages of the snakes in the actual sample. The most plausible
mortality rates are 60% in the first-year young and 50% in each
subsequent year. These rates would give the following numbers (each
rounded to the nearest whole number) of survivors from an initial cohort
of 324: 130, 65, 32, 16, 8, 4, 2, and a single individual living into the
ninth year. Probably few C. v. viridis live to be older than eight years in
the wild, although prairie rattlesnakes have been known to survive
considerably longer in captivity.
In the sample of 154 C. v. viridis there were four tapered Type II
incomplete rattles that were each estimated to have had at least 12
segments if the rattles had been intact; probably they were at least five
years old. Eight others with missing segments but no taper (Type III
rattles) were those of relatively old snakes that probably had lost six or
more segments previously. Their rattles had 3 segments (in 3), 5 (in 2), 6
(in 2) and 8 (in 1 ). On the basis of size and number of rattle segments any
of them could have been as young as six or seven years, but might have
been much older, perhaps as old as 12 to 15 years.
Timber rattlesnake. Table 3 shows the numbers of timber rattlesnakes
of each sex and of various sizes and rattle numbers in a fall-spring sample.
It shows that first-year young with only the postnatal button were far more
numerous than snakes of any other rattle number, comprising 37% of the
total. My age correlation is based upon the fact that first-year and second-
year snakes constitute recognizable cohorts, the former with one rattle, the
button, and the latter with usually three rattles, sometimes four. The
divisions among older snakes with longer rattle strings are made partly on
8 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY
the basis of deduction from the known rate of development in the first
year, and partly on the basis that free-living timber rattlesnakes, including
adults, have gained two rattle segments per season in known instances.
The sample of 100 timber rattlesnakes in Table 3 is subject to biases of
various sorts. On the University of Kansas Natural History Reservation
where most of the records were obtained, no full-grown adults (exceeding
90 cm snout-vent length) were captured in traps because the traps' funnel
entrances were too small, averaging only 2.5 to 3.0 cm in diameter. Most
captures of immature snakes (53 of 70) were made in these traps. The sex
ratio was close to parity in the overall sample, 52 males to 48 females, but
with ratios changing as follows: in first-year young, 16 males to 21
females; second- and third-year young, 17 males to 10 females; adults, 19
males to 17 females.
Of 16 large snakes (100 cm or more SVL) only two had intact rattles,
of 10 and 16 segments. Nine of the 16 had untapered, Type III rattles,
suggesting that since attainment of full size, each had lost part of its string
including the natal button and at least six terminal segments acquired
during its first three years while rapid growth was occurring. Thus, for a
snake with ten rattles of uniform width, a minimum age of eight years
could be estimated— five years to produce the ten adult rattles, plus three
more years to produce earlier smaller segments that were subsequently
lost.
The ratio of first-year to second-year young changed seasonally, 32 to
12 in fall, 9 to 5 in spring. The fact that the youngest cohort was 2.7 times
as numerous as the next oldest cohort in fall but only 1.8 times as
numerous in spring suggests that approximately one-third of them did not
survive their first winter. Presumably they were subject to a comparable
mortality rate during their months of activity.
Records of young per litter in Kansas C. horridus include one of 6
young (Collins, 1982), another of 8 (KU) and counts of follicles palped in
the live snakes or in dissected specimens as follows: 5,5,6,9, 10, 11, 11,
14. For the combined total of 10 litters the mean is 8.5 ±0.91. Evidently
the female cycle is most often triennial, judging from the findings of W. S.
Brown and W. H. Martin III, but a biennial cycle may occur in some
Kansas females. Those that were gravid had rattles of at least 7 segments
and were longer than 800 mm, SVL. On the basis of size and rattle number
they were believed to be in their fourth year or older. Hence, the first three
annual cohorts, including first-year with only a button or 2 rattles (SVL
298-495 in 37), second-year, 3 or 4 rattles (SVL 548-670 in 14), and
third-year, 5 or 6 rattles (SVL 504-855 in 13), are considered immatures.
Like other rattlesnakes, Crotalus horridus is known to produce stillborn
young and abort infertile eggs frequently. William S. Brown (pers.
comm.) found that in Warren County, New York, 186 eggs ovulated by 20
females produced 149 living young, 12 stillborn, and the remaining 25
were infertile. Thus only 80% produced viable young. If a similar ratio
applies in the Kansas population studied, litters would average 6.8 living
young. In the fall-spring sample of 100 snakes, 36 are adults and 17 of
these are females, about one-third of which may be fecund each year if
DEMOGRAPHY OF KANSAS RATTLESNAKES
Table 3. Timber rattlesnakes (Crotalus korridus) of a spring-and-fall
sample of 100 from northeastern Kansas, divided into age cohorts on
the basis of size (SVL) and rattle segments. B = button.
Tentative
Number of
rattle
segments
SVL in mm
N
age cohort
X
range
/
First-year
First-year
Second-year
Second-year
Third-year
Third-year
Fourth-year
Fourth-year
Fifth-year
Fifth-year
Sixth-year
Seventh-year
Eighth-year
Ninth-year
Tenth-year
Button
2(1+B)
3 (2 + B)
4 (3 + B)
5 (4 + B)
6 (5 + B)
7 (6 + B)
8 (7 + B)
9 (8 + B)
10 (9 + B)
11 and 12
(10 and 11 +B)
13 and 14 (est.)
14, 16. 16. 16 (est.)
17 (5 est.), 18 (f est.)
19 (est.)
371
495
603
605
720
840
842
906
932
1001
1013
(298-413)
(548-665)
(577-670)
(504-802)
(814-855)
(800-870)
(812-995)
(898-991)
(966-1031)
(922-1082)
(1142-1230)
(1010-1175)
(1038-1196)
(1000)
37(15-22)
1 (0- 1)
10 (7-
4 (2-
9 (6-
4 (2-
7 (2-
8 (3-
5 (3-
2 (0-
4(3-
3)
2)
3)
2)
5)
5)
2)
2)
1)
2 (2- 0)
4 (4- 0)
2 (1- 1)
1 (0- 1)
Table 4. Comparison of demographic traits in Kansas prairie
rattlesnakes (Crotalus viridis) and timber rattlesnakes (Crotalus
horridus). Means are shown with standard errors.
Crotalus viridis
Crotalus horridus
Female age at maturity
third year
fourth year
Incidence of fecundity
in adult females
70%
33%
Litter size
10.1 ±0.8 (5-18)
8.5±0.9 (5-14)
Estimated live births
per litter
8.8
6.8
Percentage survival
through fifth year
2.5
17.3
Adult snout-vent length, mm
Male
x = 932±14.5
x= 1092 ±22.7
811-1038 (n = 20)
980-1270 (n= 14)
Female
x = 873 ±10.6
x = 987±21.2
783-950 (n= 16)
895-1038 (n = 7)
Adult weight, gms
Male
x = 487±33.8
x = 891±72.5
295-655 (n=ll)
580-1874 (n=10)
Female
x = 339±14.2
x = 557±47.3
265-435 (n= 1 1)
388-883 (n=ll)
First-year young
(fall-spring)
Snout- vent length, mm
x = 335±6.7
x = 364±7.2
291-360 (n=13)
298-423 (n = 31)
Weight, gms
x=13.7±1.2
x = 33.94±1.5
9-18 (n=ll)
23-55 (n = 31)
10 OCCASIONAL PAPERS MUSEUM OF NATURAL HISTORY
they are on a triennial schedule. These 17 females each reproducing
triennially would total an average of about 39 young annually. The small
and inconspicusous first-year young were not caught in their true numbers
in relation to adults, even though many of them were caught in live-traps
that were not effective for catching the adults. As in the case of C. viridis,
various mortality rates were empirically tested against the figures at hand
for estimated ages of the snakes in the actual sample. A mortality of 45%
in first-year young and 25% annually, thereafter, seems most plausible and
would result in the following numbers of survivors in successive years,
from the original cohort of 39 newborn young: 21, 16, 12,9,7,5,4,3,2,
2 and a single survivor living into the 11th year.
Table 3 shows concentrations of young timber rattlesnakes with rattles
having 1, 3, 5 and 7 segments, the modal numbers for first-year, second-
year, third-year and fourth-year categories, whereas relatively few in the
fall-and-spring sample had the intermediate numbers of 2, 4, and 6
segments.
DISCUSSION
In both the timber rattlesnake (Crotalus horridus) and the prairie
rattlesnake (C. viridis) population, turnover in Kansas is fairly rapid, with
newly matured adults making up a high proportion of the populations.
However, in all respects the prairie rattlesnake shows more life history
traits that emphasize high reproductive potential and an accelerated life
cycle, whereas the timber rattlesnake has, instead, much lower reproduc-
tive potential and greater longevity. Judging from information available in
the literature, the same contrast applies, in varying degrees, between the
prairie rattlesnake in Kansas, and various other species and subspecies
elsewhere, including the more western subspecies of C. viridis. The
climatic extremes and the open terrain in the area occupied by C. v. viridis
perhaps result in a higher incidence of mortality from both predation and
weather, compared with C. horridus.
One of the most impressive characteristics in each sample was its
variability. Snakes of any given rattle number spanned a wide size range,
and those of any size category were variable in number of rattles. Growth,
much accelerated in some and retarded in others, is seemingly controlled
by a combination of innate genetic traits and the effects of fluctuating
environmental factors. In northern Idaho, Diller and Wallace (1984) found
that females of C. v. oreganus, at the onset of sexual maturity, varied from
550 to 630 mm SVL, and had four to nine rattles. Probably those of the
present study were equally variable, although minimum size and minimum
rattle number at sexual maturity were both markedly higher.
For both C. viridis and C. horridus there was notable constancy in size
of the natal button, but gain in the size of each new rattle was highly
variable. Gain in diameter from the button to the second rattle, from the
second to the third, or from the third to the fourth, was negligible in some
individuals, and as high as 40% in others (Table 1).
DEMOGRAPHY OF KANSAS RATTLESNAKES 1 1
ACKNOWLEGMENTS
My sincere thanks are proferred to all those who helped me with this
study or participated in it. My wife, Virginia R. Fitch, accompanied me on
field trips and helped with the capture and recording of prairie rat-
tlesnakes, and also deserves thanks for typing the manuscript and reading
it critically. Steve Barnum allowed me to examine recently captured
prairie rattlesnakes in his possession. Gary Norton and Ed Anderson
allowed me to examine their collections of detached rattles. William S.
Brown and W. H. Martin III made available their records of timber
rattlesnakes in northern New York and Shenandoah National Park,
respectively. Joseph Slowinsky, Stanley Rassmussen and George Pisani
participated in searches for timber rattlesnakes. William E. Duellman
permitted me to examine specimens in the University of Kansas Museum
of Natural History, and Eugene D. Fleharty permitted me to examine those
in the Museum of the High Plains, Fort Hays State University. William S.
Brown and Richard A. Seigel read the manuscript critically and made
many helpful suggestions. Travel in 1983-84 was supported by the Kansas
Fish and Game Commission Non-game Wildlife Program.
LITERATURE CITED
Aldridge, R. D. 1979. Female reproductive cycles of the snakes Arizona elegans and
Crotalus viridis. Herpetologica, 35: 256-261.
Collins. J. T. 1982. Amphibians and reptiles in Kansas. Univ. Kansas Mus. Nat. Hist. Pub.
Ed. Ser. No. 8: 1-356.
Diller, L. V. and R. L. Wallace. 1984. Reproductive biology of the northern Pacific
rattlesnake (Crotalus viridis oreganus) in northern Idaho. Herpetologica, 40:
182-193.
Fitch. H. S. 1949. Study of snake populations in central California. American Midland
Naturalist, 41: 513-579.
Heyrend, F. L. and A. Call. 1951. Growth and age in western striped racer and Great
Basin rattlesnake. In Symposium: A snake den in Tooele County, Utah. Her-
petologica. 7: 28-40.
Klauber, L. M- 1956. Rattlesnakes; their habits, life history and influence on mankind.
Univ. California Press, Berkeley, 2 vols., xvii+ 1476 pp.
Marr. J. D. 1944. Notes on amphibians and reptiles from the central United States.
American Midland Naturalist, 32: 478-490.
Rahn, H. 1942. The reproductive cycle of the prairie rattler. Copeia, 1942: 233-240.
University of Kansas Publications
MUSEUM OF NATURAL HISTORY
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