Why do some birds (Even of same species) fly south in winter , while others stay put?
some fly away because of lack of food, if you are on about certain species, like swallows and european robbins, the females fly south for the winter to feed and bulk up, while the males stay, endure the winter and build the most impressive nests they can, so that they can impress the females when they get back then the highest ranking females choose the male with the most impressive nest and/or the best physical attributes. male robbins with the brightest/ largest red breasts tend to get chosen because it tells the females ‘i’m still alive and i haven’t been caught by predators, even though i’m highly noticeable, therefore, i am the fittest and the best =]’ Together they raise the eggs to chicks, the males, maintaining the nests and protecting the chicks, the females sit on the eggs (they have eaten well and have the warmest body temperatures) then both take turns in feeding when they have hatched.
