I don't know what kind of experts your paper has but they are not experts in weather forecasting or in bird/animal behaviour.
Birds and animals migrate due to local changes in weather, daylight hours, temperature and wind direction and whether they have enough food.
Birds fly off their summer grounds here at the same time, but if it is bad weather and colder they'll leave earlier. I don't know if any Canadian birds fly to you but mostly I guess they fly south to the states, where no doubt people there tell what the weather is going to do based on when the birds arrive, and I think they'll be wrong. Animals behave just the same.