4. HORMONES AND BEHAVIOR
229
ovulation are closely associated in time, a period of incubation follows,
and after hatching, parental behavior is displayed. In mammals any nest
building that is a part of reproduction is separated from mating and
ovulation by pregnancy and tends to be associated with parturition.
For nest building therefore the ovarian conditions are greatly different
in the two phyla and the difference in the hormonal control that is
reported need not be surprising. The second point is that many mammals
build shelters or nests which do not necessarily serve for reproduction.
Nests of this type built by domestic mice have been designated "Schlafnester" or "sleeping nests," those built by pregnant mice "Brutnester"
or "brood nests" (361, 362). Corresponding types built by rabbits are
called "straw" and "maternal" nests (363). The construction of both
may be influenced by hormonal action, the latter as we shall see, by
ovarian hormones, and the former as an indirect response to a deficiency
of thyroid hormone when there is a need for regulation of the body
temperature (39, 362).
The relationship between the hormones and construction of the brood
or maternal nest seems to have been studied only in the rabbit and
mouse. In the former species this type of nest is built prior to or at
parturition by lining the straw nest with fur plucked from the rabbit's
own body (364). At this time the progesterone:estrogen ratio is reversed
(365). Experimentally, maternal nest-building behavior has been induced by removal of the corpora lutea (332, 366), removal of the gravid
uterus which led to an involution of the corpora lutea (367), removal of
the conceptus mass between days 20 and 27 of gestation, and by ovariectomy between days 20 and 24 (363). Parturition and all of these procedures result in what Zarrow and his associates (363) call a "hormonal
upset," but beyond indicating that estradiol, progesterone, and possibly
prolactin are involved, there seems to be little that can be added.
Nonpregnant mice provided with hay will build a nest each night
which can be removed and weighed the following morning. The amount
used by the mice in Kollers (361, 363) experiments weighed from 7 to
11 grams. Pregnant females, on the other hand, build much larger nests
starting abruptly the 4th to 5th day of pregnancy, which is the time the
corpus luteum of pregnancy becomes histologically demonstrable. Confirmation of the belief that progesterone is involved was given by the
marked increase in the nesting material used by intact nonpregnant and
gonadectomized mice after 2 or 3 daily injections of this hormone. Koller
(361, 362) reported also that the introduction of young mice into the
cage with an adult female induced an abrupt increase in nest-building
activity. As Lehrman (7) notes, this ability of young mice to stimulate
229
ovulation are closely associated in time, a period of incubation follows,
and after hatching, parental behavior is displayed. In mammals any nest
building that is a part of reproduction is separated from mating and
ovulation by pregnancy and tends to be associated with parturition.
For nest building therefore the ovarian conditions are greatly different
in the two phyla and the difference in the hormonal control that is
reported need not be surprising. The second point is that many mammals
build shelters or nests which do not necessarily serve for reproduction.
Nests of this type built by domestic mice have been designated "Schlafnester" or "sleeping nests," those built by pregnant mice "Brutnester"
or "brood nests" (361, 362). Corresponding types built by rabbits are
called "straw" and "maternal" nests (363). The construction of both
may be influenced by hormonal action, the latter as we shall see, by
ovarian hormones, and the former as an indirect response to a deficiency
of thyroid hormone when there is a need for regulation of the body
temperature (39, 362).
The relationship between the hormones and construction of the brood
or maternal nest seems to have been studied only in the rabbit and
mouse. In the former species this type of nest is built prior to or at
parturition by lining the straw nest with fur plucked from the rabbit's
own body (364). At this time the progesterone:estrogen ratio is reversed
(365). Experimentally, maternal nest-building behavior has been induced by removal of the corpora lutea (332, 366), removal of the gravid
uterus which led to an involution of the corpora lutea (367), removal of
the conceptus mass between days 20 and 27 of gestation, and by ovariectomy between days 20 and 24 (363). Parturition and all of these procedures result in what Zarrow and his associates (363) call a "hormonal
upset," but beyond indicating that estradiol, progesterone, and possibly
prolactin are involved, there seems to be little that can be added.
Nonpregnant mice provided with hay will build a nest each night
which can be removed and weighed the following morning. The amount
used by the mice in Kollers (361, 363) experiments weighed from 7 to
11 grams. Pregnant females, on the other hand, build much larger nests
starting abruptly the 4th to 5th day of pregnancy, which is the time the
corpus luteum of pregnancy becomes histologically demonstrable. Confirmation of the belief that progesterone is involved was given by the
marked increase in the nesting material used by intact nonpregnant and
gonadectomized mice after 2 or 3 daily injections of this hormone. Koller
(361, 362) reported also that the introduction of young mice into the
cage with an adult female induced an abrupt increase in nest-building
activity. As Lehrman (7) notes, this ability of young mice to stimulate