It is an observational truth that we do not sight overweight, fat or obese birds around us. (This excludes birds like the broiler chickens which are given special diet to grow fast and big for certain specific purposes.) At least I have not seen one during all my years on earth. Do birds have secret gyms? Do they exercise in their nests or caves? Do they do dieting? Not to my knowledge.
Birds do not get overweight for a number of reasons the most important of which, in my analysis, is: ratio of food intake to activity in terms of calories (energy) is near equal to unity. Birds lead natural lives and there is nothing better than natural in matters of health. Why birds alone? I have not come across any animal or insects having those unwanted extra inches on them like some humans. If birds do not have good health, they either recover through natural processes or simply die. There are no hospitals for them, no medical bills and none of those rapacious health insurance companies and physicians. But for the resting time and the time when they feed their young ones, birds are constantly on the move in air, mostly in search of food. There are of course the migratory birds which fly long distances once or twice a year. Birds are the greatest travelers on land.
Birds are restless and high energy beings like our children. Only domestic people or people leading sedentary life-styles can gain extra weight or fatness and that fatness leads to obesity in some cases. Over a few generations, the fatness may become hereditary. You might have noticed at times some animals or birds appearing fat; they are either the expectant mothers or their stomachs are full. Birds do not gain extra weight even when kept in cages; observe carefully and you will notice that. They may look lean if sick or starving. Birds’ constitutions are built that way because they have to fly almost all the time and it is not an easy thing to fly on your own, without any external aids, when you are heavy. This optimization between body-weight and flying activity has come through millions of years of biological evolution.
By Dr. Sachidanand Das