According to Cornell Laboratory of Ornithology ecologist Frank La Sorte, changes in precipitation and temperature that occur around August, a time when many migratory birds are preparing for their fall migration.  This is the time when the birds are gorging themselves on variety of fruits, berries and other foods.  This feeding frenzy enables them to store the fuel required to successfully to wing their way to their winter homes.

       Utilizing population estimates of 77 species of migratory birds and climate models, La Sorte found that weather changes could have a negative impact on the availability of many of the foods the birds heavily rely on to prepare for the arduous migration.  Birds that attempt to migrate without adequate fat reserves reduce their chances of surviving the marathon trip.