Biology_of_Mustelids_Vol_1.pdf

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percentage ratio of the external width of the canines to the width of
their pulp cavities, both measured at the root of the tooth.
statistical
analysis of these measurements enabled us to subdivide all the specimens
collected into three age groups :
(a)
this year's brood (age up to 1 year), with a pulp cavity index
of 100 (hollow tooth) to 20 for males, and 100 to 16.5 for females;
(b) adult (1.5-2.0 years), with a pulp cavity index of 19.5-10.5
for males, and 16.0-9.5 for females;
(c)
old (2.5 years and over), with a pulp cavity index of less than
10.0 for males, and less than 9.0 for females. In addition, rings (layers)
were to be seen in the tooth root cement in animals older than 2.5 years.
This method can distinguish the age groups with a reliability
fluctuating between 98 and 99% for males and 96-98% for females:
hence,
the only errors possible are that a few specimens from the adult group could
be classified as young, but not vice versa.
When the procedure was checked
on 26 captive ermine of known age, it was confirmed as reliable.
All the data which we analysed are given in Table 1.
The age
structures are similar in males and females from the different regions.
For example, in Northern Kazakhstan, the young of the year comprised 64.2%
of the males and 65.0% of the females;
equivalent figures were 90.0 and 89.9%.
in North Tyumen' province the
The sex ratios for males and
females are also similar in different years so we do not therefore subdivide
the data by sex.
The young of the current year are always the largest class in
the population (see Table 1).
The adults comprise 25%, and the ~ld
ermine only 2.5% (i.e. 10 times less than the adults).
One would expect
from this that the proportion of ermine older than 3.5 years would not
exceed 0.1%;
in practice there may be none at all, even when quite large
numbers are handled (up to a thousand specimens a year from one place).