WHY DO QUAIL EGGS HATCH AT THE SAME TIME?

Some quail species lay up to 8 eggs over a period of 8 days at a rate of one egg per day. Surprisingly, after 21 to 23 days of incubation, all eggs hatch within 6 hours.

If the eggs developed over a uniform rate, they would hatch one per day over an eight-day period. Why does that not happen? Scientists believe that chicks communicate with each other within the eggs and break out of the eggshells at the same time.