Doubtless, their need for a reliable food supply is the answer rather than the onset of wintry weather, since many small birds that have difficulty surviving cold winters do not migrate.
Kahtlemata ei ole vastuseks saabuvad talveilmad, vaid vajadus leida piisavalt toitu, sest paljud väiksed linnud ei rända, kuigi neil on raske külma talve üle elada.