Large birds like pheasants often walk short distances. small birds like chickadees never walk. they either hop or fly. why might this be? physics

The maximum probable speed of walking is restricted mainly by two factors, that is, the length of the leg and the free fall acceleration. The animals with longer legs exhibit higher maximum walking speed, while the animals with very short legs exhibit low maximum walking speed.  

The large birds like pheasants usually walk brief distances, however, birds like chickadees never walk. In the case of pheasants, they exhibit a higher maximum walking speed, on the other hand, the chickadees exhibits a low maximum walking speed. Thus, the chickadees should never walk, they should fly or hop.  

Also, more energy is utilized in flying than in walking. Therefore, large birds like pheasants usually walk brief distances so that energy can be saved.  

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.