Some migratory birds are heterothermic, meaning they sometimes maintain a constant body temperature and other times allow their body temperature to vary. For example, on cold nights, they sometimes reduce their metabolic rate and allow their body temperature to drop as the air temperature falls. Which of the following hypotheses about this unusual strategy is consistent with what you learned in this section? A. Birds allow their temperature to drop in order to increase their assimilation efficiency.
B. Birds allow their temperature drop in order to increase their production efficiency.
C. Birds allow their temperature to drds in order to increase their consumption efficiency.

B. Birds allow their temperature drop in order to increase their production efficiency.

Explanation:

Most birds can drop the temperature a few centigrade degrees, while there are torpid birds capable of lowering much more. Birds can drop body temperature in response to environmental conditions. Bird species including, among others, swifts, hummingbirds and chickadees are capable of regulating body temperature during torpor state. There are different morphological and behavioral adaptative traits that enable birds to minimize the cost of thermoregulation. In the first place, epidermis surface allows heat loss to the environment, while arteries and veins in the legs help to retain heat in cold conditions.

"a.) well–developed vascular system."