What is macroeconomics?

Macroeconomics is the study of large scale economic issues such as those which affect the entire economy. This is in contrast to Microeconomics which looks at smaller scale economic principles. Macroeconomics is a highly practical discipline as it deals with principles that directly impact every part of life.

ans.

heterothermic organisms include those organisms that can switch between homeothermic (having body temperature higher than environment) and poikilothermic (having variation in internal body temperature) strategies.

some migratory birds show heterothermy as they decrease their metabolic rate during cold nights to keep their body temperature low. drop in metabolic rate allows increase in production efficiency of birds that reduces the internal body temperature to make it equal to external cold temperature during cold nights.

thus, the correct answer is 'birds allow their temperature drop in order to increase their production efficiency.'