PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

condition differ) ; the turnover rate o f
the population, and the intensity o f
metabolism of different groups of animals
. . . Whilst it is not difficult to estimate
the intensity of metabolism of certain
species in a calorimetric chamber, i t
is practically impossible to estimate the
loss of energy by a bat, a mole, or a
dolphin in the process of their natura l
life activity .
In the light of these considerations we wil l
examine our preliminary data and, through a
comparison of actual and needful information,
delineate the work still to be done .
Small Mammal Studies
Since small mammals are generally inconspicuous,
and do not make readily detectable
signs, the determination of species presence
and especially population density is widely
recognized as a difficult problem .
The most commonly used method fo r
estimating population densities in smal l
mammals is to capture, mark, and release a
sample, and then capture a second sampl e
containing both marked and unmarked individuals
. Several underlying assumption s
(Leslie 1952) are : all individuals have equa l
probabilities of capture, released individual s
disperse randomly into the populations, an d
there is no mortality, natality, or significan t
ingress or egress during the experimenta l
period .
Since these assumptions were not war -
ranted in our case, and since we needed to
collect specimens for data on weight, foo d
habits, and reproduction, we considered intensive
removal methods . Grodzinski et al .
(1966) proposed such a method for IBP smal l
mammal studies. They suggested intensive
kill-trapping following a prebaiting period on
a defined grid of locations . This provided data
for an estimation procedure in which a regression
line, plotted for the number of animals
caught each day (on the ordinate axis) against
the cumulative number previously caught ,
would provide an estimate of populatio n
density (the point where the regression line
intersected the abscissa) . Earlier work on this
approach was that of DeLury (1947), Hayn e
(1949), and Zippin (1958) .
The major flaw in the method of Grodzinski
et al. (1966) is that it gives no accurat e
estimate of the area sampled by the grid, be -
cause the small mammals move some unknown
distance to the trapping point . Sinc e
the area sampled is not defined, populatio n
densities cannot be determined .
Adamczyk and Ryszkowski (1968) suggested
that the sample grid be surrounded o n
each side by an external belt of trapping locations
to catch animals moving toward th e
inner grid before they could reach it, thereb y
controlling the "periphery effect ."
The data provided by the external trappin g
belt cannot be used, because the distance
travelled by each animal before being caught
is highly variable (Miller 1970) .
Adamczyk and Ryszkowski (1968) recommend
a 5-day prebaiting period to accusto m
the mammals to the trap locations, followe d
by a 5-day period of removal trapping . Their
basic assumptions are : (1) all residents of the
inner grid are captured, (2) prebaiting does
not increase the resident density, and (3) individuals
not resident on the inner grid are no t
captured on the inner grid ; immigrants and
individuals resident in the outer grid will b e
captured, if at all, in the outer grid .
Of these three assumptions, we could tes t
only the second . Adopting a 5-day prebaiting
period, we ran pairs of trap-lines-one pre -
baited and one control-in each case . Total
catches over 5 days were not different,
though prebaited lines took a higher proportion
of the catch on the first day (Mille r
1970) . This finding corroborates that o f
Babinska and Bock (1969), who showed tha t
prebaiting did not significantly increase th e
density of resident small mammals .
Our trapping procedure was as follows : a
5 .94-ha (12 .4-acre) sample area was divide d
into 256 stations, 16 rows by 16 lines, wit h
15 .2-meter spacing . Anchored at each statio n
was a paper plate which was baited with oatmeal,
millet, sunflower seeds, oats, and wheat
for 5 days . Then the remaining bait was removed
and two mouse traps were placed on
each plate, one trap baited with a peanut
butter-bacon grease mixture, and the other
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