tween the sexes were not found. 
had been marked. They were weighed at each recapture 
and their weights were plotted on the graph at the 
proper intervals. All points on the graph up to 3 pounds 
were then used to construct a new line by eye. The 
weights of all raccoons which weighed more than 2 but 
less than 3 pounds the first time they were captured 
were then placed on the recently established line and 
the ages of these animals were estimated. These animals 
also were weighed at each recapture and their weights 
were plotted on the graph at the proper intervals. All 
points on the graph up to 4 pounds were then used to 
construct a new line by eye. A similar procedure was 
repeated for each 1-pound weight class up to 7 pounds. 
The first lines drawn for each 1-pound weight class 
were then ignored, and a new line was established by 
plotting the mean weights within each pound class in 
relation to the mean estimated age of the animals, fig. 2. 
The line established in this manner provided the basis 
for determining the ages for all juvenile raccoons up to 
7.0 pounds of weight when taken prior to November 1. 
These weight-time limitations were arbitrary, but, up 
to November 1, juvenile raccoons are rather easily 
recognized by weight, conformation, pelage, appearance 
of the nipples in the females, and development of the 
penis in males (Sanderson 1950:395—-6). After Novem- 
ber 1, some juveniles reach adult weights, and some 
adults lose weight because of critical food conditions 
at this time and the fact that raccoons may remain in 
dens and without food for several days during periods 
of severe weather. Significant weight differences be- 
It was concluded that 
age could be estimated in months, on the basis of body 
weight, for male and female raccoons weighing 7 
pounds or less and caught prior to November 1. 
If an animal could not be classified as a juvenile 
when first caught, its minimal age was determined. 
For example, a lactating female or an adult male caught 
in July would have a minimal age of 15 months. 
In Illinois, raccoons do not breed until they are approxi- 
mately 10 months of age or older. Because most rac- 
coons in the northern half of Illinois are born during 
April, this was assumed to be the month of birth when 
exact information was not available. Of course, an 
animal might have been 1 or more years older than its 
minimal age. 
The epiphyseal cartilage, the second criterion inves- 
tigated as a possible means for estimating age in rac- 
coons, was studied in both living and dead animals. 
The age classification of epiphyseal cartilages used here 
is adapted from that of Hale (1949:217) for cotton- 
tail rabbits (Sylvilagus floridanus). Unless otherwise 
indicated, references to epiphyseal cartilage apply only 
to that of the ulna and the radius. 
Epiphyseal closure was studied in several captive 
raccoons of known ages by photographing their radii 
and ulnae by X-rays. Photographs were taken at irregu- 
lar intervals until the epiphyseal cartilage disappeared. 
Live raccoons were anesthetized prior to being photo- 
graphed, but no special preparation was needed for the 
occasional dead 
graphed. An intraperitoneal injection of pentobarbital 
sodium (nembutal), at the rate of 1 per 4 pounds 
of body weight, produced deep anesthesia in most rac- 
raccoon whose epiphyses were photo- 
coons within 5 to 10 minutes. 
taken at a distance of 
milliamperes, with an exposure of 
were developed by routine methods used for regular 
The photographs were 
at 92 kilovolts and 10 
4.5 seconds. They 
30 inches, 
film, and the negatives were examined. 
Broad bands of epiphyseal cartilage are present in 
The cartilage plates 
are replaced by bony tissue as the raccoon grows older. 
All epiphyseal plates examined directly or by X-ray 
photographs were classified as closed, thin, or broad. 
Closed means that no cartilage is present. Broad indi- 
cates a thick plate of epiphyseal cartilage. When bones 
in this stage of development are cleaned, the epiphysis 
or head either separates from the shaft or is only loosely 
attached. In an X-ray photograph, space appears be- 
tween the head and shaft of the bone. Thin indicates 
an intermediate condition between closed and broad. 
In bones in this condition, the head remains attached 
to the shaft after cleaning, but a groove indicating the 
presence of cartilage is readily visible. In an X-ray 
photograph the cartilage appears as a shadow, but there 
is no space between the head and the shaft of the bone. 
Bones from dead raccoons of known ages 
cleaned by boiling, and then the epiphyseal plates were 
examined directly. 
Each time the epiphyses of a raccoon were photo- 
graphed by X-ray, the animal’s age, actual for an 
animal born in captivity and estimated for one born in 
the wild, was recorded. Not Ss of the 
were included in tables 4 and 5. In a raccoon whose 
epiphyses were photographed more than once, only the 
maximum age at which broad epiphyses were evident, 
only the minimum and maximum ages at which thin 
the leg bones of a young raccoon. 
were 
observations 
epiphyses were evident, and only the minimum age at 
which epiphyseal closure was evident were included in 
these tables. Several captives were repeatedly photo- 
graphed by X-rays to determine when the epiphyseal 
cartilage disappeared. These repeated observations of 
the same animals made it possible to determine the 
length of time thin epiphyses were present in indi- 
viduals. 
The penis bone, 
gated, was studied in dead males. 
the third aging criterion investi- 
When a male, 
captive or wild, of known age died, its penis bone was 
collected. A fresh baculum was cleaned easily by scrap- 
ing with a pocket knife. A dried baculum was best 
cleaned by scraping after being boiled in water. After 
it was cleaned, the baculum was examined for indica- 
either 
tions of age, including photographing by X-rays in some 
cases. The critical points examined for age estimation 
were degree of ossification of the distal tip and, in some 
cases, the degree of ossification of the basal end of the 
bone. 
o 
