Biology_of_Mustelids_Vol_1.pdf

189.
From examination of many data on the feeding of the ermine, research
workers have concluded that the main factor influencing the numerical varia-
tions of this species is a change in the food supply.
Years of high, or
low, ermine numbBr~
often coincide with good, or bad, years for its main prey,
the mouse-like rodents and especially the common vole and the water rat.
This is confirmed by the results of our investigations {Tables 1, 2 and ~)(a)
and by information already published (Zverev 1931, Grigor'ev and Teplov 1939,
Lavrov 1941, Nasimovich 1948).
On the causes of the instability in numbers of the ermine, for
instance, Aspisov and Popov (1940) wrote:
"The significance of this factor
[state of supplies of water rat] in the Gor'kovsk and Kirovsk provinces,
and the Tartar, Bashkir and Mariisk republics has been proved •••• This
factor can be used now to compile a forecast of ermine harvest [in the next
year] from the pelt figures for the water rats in the second quarter of the
current year".
In the opinion of Nasimovich (1948):
"The fluctuation in numbers
of ermine in the north is entirely determined by variations in the supplies
of voles, since this predator, in the conditions of the Kolsk peninsula and
of the greater part of the USSR (Formozov 1935a) is a typical myophage".
On the basis of our own research, literaturH sources, masses of
information from correspondents, and the results of analysis of pelt harvests,
we recomme~ded
(Lavrov 1941) that, when compiling a forecast of the ermine,
the main consideration be given to the population density of small rodents
and water rats in the past and current years.
It was also mentioned that
population increases or declines in ermine usually continue for 1-5 years;
years with the highest yield recur every 5-9 years and the pelt harvest
varies by a factor of 3-7 (Lavrov 1941).
As from 1941, disagreements between our forecasts and the actual
(a) Identification of stomach and intestine contents of ermines was carried
out by A.P. Rozarenova and myself. - Author