4. HORMONES AND BEHAVIOR
221
ment and ovulation the variation is not great. In fowl (281, 283, 284,
299), as in mammals (143, 146), this is a time when estrogen and
progesterone are being produced, and in fowl and in the ring dove, as
in mammals, these hormones function synergistically to produce growth
and secretory changes in the genital tract (300-304). A familiarity with
this background and with the report that squatting behavior by female
chicks was induced by diethylstilbestrol and progesterone together
rather than by either substance alone (285), led Lehrman and Brody
(304) to suggest that the normal cycle in the ring dove includes a period
of estrogen secretion concurrent with nest building followed by a period
of progesterone secretion associated with incubation behavior. Confirmation of this hypothesis was believed to be given by the display of a
readiness to incubate within a few minutes after the birds injected
with progesterone were placed with a mate in cages containing a nest
with two eggs (243). No increase in crop weight was associated with
the onset of this behavior or with the hormonal treatment which induced
it, a fact which seemed to demonstrate that prolactin was not involved.
It is unfortunate that most of the data bearing on the relationship of
the hormones to incubation in birds have been obtained from so few
species. As Eisner (5) points out, it may not be assumed that the onset
of incubation is mediated by progesterone in species other than doves.
Furthermore, the fact that oviducal changes in birds are produced by the
synergistic action of estrogen and progesterone suggests that, in some
species, incubation may be induced by the successive action of these
hormones. If progesterone alone is responsible for incubation, as the
report by Lehrman (243) would lead us to believe, the action is unusual,
for in birds and in mammals generally, when progesterone is effecting
a reaction the relationship is synergistic with an estrogen. Despite these
concerns, the important point is that incubation behavior was induced
by an ovarian hormone without any evidence of prolactin participation.
Increasing in amount as prolactin does with incubation, and decreasing
sharply when the chicks are hatched (290, 291), the possibility must be
considered that its production during incubation is in anticipation of
some role in the preparation for parental care. As we stated above in
connection with the relationship of the hormones to parental care by the
male, this is something that cannot be excluded despite the developing
opinion that any action is mainly facultative (5, 7).
Many reports reviewed by Marshall (-230), Parkes and Marshall
(208), and van Tienhoven (299) indicate that androgenic, estrogenic,
and gestagenic substances are produced by both males and females.
Relative quantities in the sexes are not given. Progesterone has been
detected on chromatograms of extracts of maturing and ruptured follicles
221
ment and ovulation the variation is not great. In fowl (281, 283, 284,
299), as in mammals (143, 146), this is a time when estrogen and
progesterone are being produced, and in fowl and in the ring dove, as
in mammals, these hormones function synergistically to produce growth
and secretory changes in the genital tract (300-304). A familiarity with
this background and with the report that squatting behavior by female
chicks was induced by diethylstilbestrol and progesterone together
rather than by either substance alone (285), led Lehrman and Brody
(304) to suggest that the normal cycle in the ring dove includes a period
of estrogen secretion concurrent with nest building followed by a period
of progesterone secretion associated with incubation behavior. Confirmation of this hypothesis was believed to be given by the display of a
readiness to incubate within a few minutes after the birds injected
with progesterone were placed with a mate in cages containing a nest
with two eggs (243). No increase in crop weight was associated with
the onset of this behavior or with the hormonal treatment which induced
it, a fact which seemed to demonstrate that prolactin was not involved.
It is unfortunate that most of the data bearing on the relationship of
the hormones to incubation in birds have been obtained from so few
species. As Eisner (5) points out, it may not be assumed that the onset
of incubation is mediated by progesterone in species other than doves.
Furthermore, the fact that oviducal changes in birds are produced by the
synergistic action of estrogen and progesterone suggests that, in some
species, incubation may be induced by the successive action of these
hormones. If progesterone alone is responsible for incubation, as the
report by Lehrman (243) would lead us to believe, the action is unusual,
for in birds and in mammals generally, when progesterone is effecting
a reaction the relationship is synergistic with an estrogen. Despite these
concerns, the important point is that incubation behavior was induced
by an ovarian hormone without any evidence of prolactin participation.
Increasing in amount as prolactin does with incubation, and decreasing
sharply when the chicks are hatched (290, 291), the possibility must be
considered that its production during incubation is in anticipation of
some role in the preparation for parental care. As we stated above in
connection with the relationship of the hormones to parental care by the
male, this is something that cannot be excluded despite the developing
opinion that any action is mainly facultative (5, 7).
Many reports reviewed by Marshall (-230), Parkes and Marshall
(208), and van Tienhoven (299) indicate that androgenic, estrogenic,
and gestagenic substances are produced by both males and females.
Relative quantities in the sexes are not given. Progesterone has been
detected on chromatograms of extracts of maturing and ruptured follicles