Leap year refers to the extra time in the Gregorian calendar, which will be used to set the leap month in the lunar calendar. In the folk, some people think that leap years and leap months are unlucky, so there will be some taboos. However, it is considered as "hatching eggs" for hens to hatch chicks, which conflicts with the leap month in leap years and will lead to bad omen.
This statement has no scientific basis and is a superstition of people. In fact, it is a normal biological behavior for hens to hatch chicks, which has nothing to do with leap years and leap months.