(1961) states that this increase in skeletal weight in pigeons 
ls due to the partial ossification of the marrow portions of 
the bone, called the medulary bone. This medulary bone has 
been reported in many species of birds. In the pigeons, medulary 
bone calcium was completely reabsorbed when injection of androgen 
and estrogen ceased. 
Estrogen produces another change in the bird, namely, 
the appearance of the brood patch, which is common to many 
species of birds. The brood patch is a defeatherized ventral 
apterium with increased vascularization of dermal tissue in that 
region. Bailey (1952) injected finches with estrogen, pro- 
ducing a complete brood patch. There was no effect resulting 
from the injection of prolactin, a pituitary hormone. Bailey 
then hypophysectionalized a number of birds and treated some 
with estrogen and some with prolactin. The estrogen-treated 
birds attained increased vascularization of the dermis in the 
ventral apterium, but no defeatherization. Upon treating these 
birds with prolactin, defeatherization occurred, and @ complete 
brood patch was formed. Bailey then concluded that estrogen 
elicits the pituitary to secrete prolactin, which completes 
the formation of the brood patch. Eisner (1961) pointed out 
that Bailey did not check the effect of progesterone, which might 
be involved in this process. It is believed that prolactin 
influences the secretion of progesterone, as shown by Meites 
and Shelesnyak (1957). Lehrman (1955) showed that the primary 
effect of prolactin is engorgement of the crop with pigeon- 
milk and suppression of sexual behavior in the Ring Dove. 
Eisner (1961) points out that repression of sexual behavior 
during incubation is due to the anti-gonad effect of prolactin | 
on androgen production. Bailey,(1952), working with California 
Gulls (Larus ecalifornicus) showed that prolactin secretion in 
the male begins at the time the testes begin to regress. 
Hormonal factors leading to the production of the brood patch 
also affect behavior of the bird. The brood patch may not be 
a necessity for incubation, although in most species the 
presence of brood patches appear to correspond with participa- 
tion in incubation. Skutch (1957), however, showed that this 
correspondence does not necessarily hold in passerines. 
Bailey (1952), for example, induced brood patches in both male 
and female passerines, where normally the male does not have 
4t. Kluijver (1961), however, observed that the male Chickadee 
normally developed a brood patch, although he does not incubate. 
Verner (1961) working with the Red=-footed Booby (Sula sula) 
found that neither parent developed a brood patch, although 
both incubated. The birds used either their feet to warm the 
eggs, or tucked the eggs into ruffled feathers. Weston (1947) 
found that the male Black-headed Grosbeak (Pheucticus melano- 
cephalus) incubated 40 per cent of the time during the day, 
but Bailey found no incubation pateh in that species. Peter- 
sen (19559 working with Bank Swallows (Riparia riparia) of which 
both parents incubate equally day and night found that males 
did not have an ineubation patch. Lehrman (1955) suggested that 
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