Fig. 19. Graph from records of blue racers marked early in life and recaptured, showing average and extreme weights in samples of different ages. Early in life the females outstrip males in growth and the size differential increases throughout life.

A few adult racers recaptured, including different individuals of small, medium, and large size, failed to make any measurable gain in length over periods of months, or even over several years. Most often the large individuals were those that failed to grow or made only slight gains. Some of the snakes that failed to increase in length suffered dramatic weight losses, perhaps as a result of injury, disease, or parasitism. However, other individuals that failed to gain appreciably in length did gain in weight. Doubtless both genetic and environmental factors were involved. A few racers gave the impression of being stunted by adversity. All records obtained of growth (or failure to grow), throughout the period of my study were used in compiling [Table 17].

Table 16. Growth in Several Racers That Were Already Adult
When Originally Captured and That Subsequently Attained Unusually Large Size

SexOriginal recordRecord(s) of recapture
DateSnout-vent
length
in mm.		Weight
in grams		Probable
age in
months		DateSnout-vent
length
in mm.		Weight
in grams		Probable
age in
months
♂May 14, 1956815191561/2May 15, 1959905243921/2
May 16, 19619452871041/2
♂May 22, 1958825251681/2June 25, 195984020582
May 27, 196088021093
Oct. 14, 19619002231091/2
♂May 19, 1959705105321/2May 28, 1960828...45
July 3, 1961900265581/2
♀Nov. 6, 195482319038June 30, 1958103035082
♀June 6, 195581019033May 21, 19591087345801/2
♀Aug. 29, 195788526548Aug. 6, 1960104123583
♀May 1, 19586338420May 30, 1961108832057
♀July 20, 1958862203461/2June 30, 1960102023870
♀Oct. 18, 1956845185371/2May 20, 1958905240561/2
Oct. 22, 1959108537574

Mortality Factors and Adaptations for Survival

Defense, and Escape

The behavior patterns that are associated with defense and escape in snakes are widespread. The common racer is typical of the more generalized snakes. Almost all elements of the racer's behavior are found in snakes of other genera and perhaps, of other families. The racer differs from these only in minor details of its behavior, in the circumstances under which various behavioral traits are elicited, and their relative importance. The common racer is one of the swiftest of North American snakes, and it usually depends upon speed to avoid enemies. Racers crossing roads may detect approaching automobiles at a distance, and thereby may be stimulated to accelerate their movements and so escape onto the shoulders rather than becoming traffic casualties as many individuals of most other kinds of snakes do under the same circumstances. The chances of such escape are of course much better on dirt roads that are relatively narrow and have a rough surface permitting efficient traction, than on wide smooth, paved highways. The snakes are somewhat reluctant to venture onto open expanses of pavement.

Table 17. Sizes of Racers of Different Age Groups in May and October

Age in
Years		Males
Snout-vent length in mm.Weight in grams
AverageTypical
range		Observed
range		AverageObserved
range
1+539432-609
2-615500-676560-67468.251-92
2+668610-700620-710107.463-134
3-706677-730648-755102.165-129
3+740701-754667-780147.093-216
4-757731-772725-809139 95-251
4+785755-793720-850167.4128-225
5- 805.5773-810743-855152.4110-198
5+810801-831773-858163.9 89-211
6-827811-831765-883175.9130-230
7-845832-850788-900181.2125-210
8-868851-873740-890217.5194-225
8+870861-884
Females
1+581415-658
2-644520-739580-73883.552-127
2+743685-804670-826135.273-200
3-810740-829730-880149.498-219
3+836804-869736-915181.2120-268
4-866830-880791-920212.3175-243
4+883870-914810-952191.2143-300
5-914880-929833-1088209.6136-275
5+932915-954883-990250.4195-336
6-965930-961892-1020245.9218-283
6+970955-980885-1003271 243-336
7-974962-990919-1050251.3150-330
7+1000 980-1015930-1085295.6235-375