SIX MEDFORD (OREGON) MAIL TRIBUNE
Tuesday, February II. 1958
Is That So?
By EUGENE BURNS
Ranger-Naturjiist
One of the major ad
vantages warm-blooded mam
mals have is that the mother
can carry her developing im
mature young out of harm's
way within her body and then
give birth at that time of the
year when survival is best
assured.
Unlike the human method
in which the embryo develops
steadily, day by day until
birth, many mammals have
developed astonishing varia
tions which can delay birth
from a few days to several
months. This seems particu
larly true in regions where
winters have become more
severe than they were in
ages past, or where food is
not plentiful during recurring
seasonal periods, or where the
mother is nursing or in poor
condition.
Although it is a matter of
recent "discovery" there are
three astonishing variations
and they occur quite regularly
In the wild animals about us.
In one group, the egg is
fertilized but then its normal
development is arrested with
in a few days. This includes
the fisher, mink, badger, arm
adillo, weasel, black bear and
marten.
In a second group, which
includes deer, rat, mice and
allied families, there may be
a definite interruption of
growth after-the embryo is
already quite well developed
the interval lasting from a
few days to several months.
With the third group, con
fined to most bats, the egg it
self is not fertilized until sev
eral months after mating
but once fertilized, develop
ment is normal.
Egg Fertilized
To take the latter group
first: most American bats,
like our common brown bat,
mate in the late summer or
fall. As far as the egg is con
cerned, nothing h a p p e n i.
Then, months after mating,
when springlike, balmy
weather arrives, the egg is
fertilized and a new life
begins. Should the winter be
prolonged, then fertilization
will be deferred. Should
spring be hastened, say by
placing the female brown bat
in a warm room, during any
time of the winter, then ferti
lization takes place and the
young will be born approxi
mately 90 days thereafter.
In the second group, the
egg is fertilized immediately
but the period of gestation, as
with the deer, may vary from
150 to 280 days! What hap
pens is this: after the egg is
fertilized and there has been
a certain amount of develop
ment, the embryo may be
come dormant for four to five
months particularly if the
mother is in poor condition.
Likewise should the weather
turn cold suddenly, the bad
ger may halt the growth of
its embryo for at least 60
to this, the first
group has a development
within the egg a few days,
then the quiescent period may
last for weeks, sometimes
even months. To all outward
appearances, there is no
change in the mother and the
pattern of her behavior is un
affected. But once growth of
the egg is resumed, it always
proceeds regularly thereafter,
regardless. Among these ani
mals is the marten, whose
gestation is about 250 to 270
days roughly, 8Vz months,
which seems excessively long
for such a small animal.
But yet, there is a much
more commonly-observed ar
rested development. It is the
bird's egg which is fertilized
when laid, yet no develop
ment takes place until cer
tain temperature requirements
have been met for a certain
number of hours. Were this
not true, the bird s young
would be hatching in the same
nest continuously over a pro
tracted period, and as a re
sult, the first-born might die
of hunger should the mother
elect to hatch out the re
mainder, or the unhatched
young might perish within
the egg should she elect to
heed the importunings of the
first-born.
Copyright 1958,
0 by Eugene Burns)
(Released by McClure
Newspaper Syndicate)
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dress your letter to: Is That
So! care Medford Mail Trib
une, Box 575, Sausalito, Calif.
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