Reasons for the others' migration shift seem focused on food opportunities. The white stork typically migrates to find food in the south when winter comes and their food supply of insects, amphibians, and other small animals dries up. But humans create trash year round, piling it up in huge, irresistible piles, a feeding opportunity that the birds just can't pass up. Another culprit? In Uzbekistan, where the storks migrated the least, researchers hypothesize that local fish farms might be supplying the birds with enough food that they don't feel the need to migrate at all.