Which of the following behaviors allows a bird to maintain a constant body temperature in extremely hot weather?
a. spreading wings
c. flattening feathers
b. panting
d. all of the above

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.