Ducks and geese prefer undisturbed air -- night air. At nighttime, the air remains relatively stable with lighter winds and less dramatic pressure and temperature gradients. In the protection of night, ducks and geese navigate toward their destinations, safe from the predation of hawks and eagles. The cooler air also keeps their body temperature down, allowing them to continue flying while burning less fat than they would during the daytime.""
A lot easier to take down US Air Airlines at night. Those nasty suckers attacked last during the day and now they need to cloak of darkness to carry out their Jhad against the US!!!