Today might be the day a bird launches into the sky on its way to you. Since it is still quite early in the migration season, that bird is more likely to be male.
Male birds leave their winter homes and arrive at their breeding grounds several days before their female counterparts. This earlier arrival of migrating males, called protandry, is common and may give the individual better access to prime territory.
Researchers have found a widening gap between the early arrival of males and later arrival of females in recent years, possibly due to increased breeding ground temperatures and the subsequent relaxation of natural selection against males arriving too early. Other researchers have looked at whether temperature at wintering grounds could impact when the birds leave, or if these differences could be predicted by a bird's restlessness behavior.