According to the Met’s excellent Heilbrun Timeline for Bruegel, the artist was trying to capture the different seasons in a commisioned series, sic:
For the Antwerp home of the wealthy merchant Niclaes Jongelinck, who owned no less than sixteen of the artist’s works, Bruegel executed a series of paintings representing the Seasons, of which five survive: Gloomy Day, Return of the Herd, Hunters in the Snow (all Vienna, Kunsthistoriches Museum), Haymaking (Prague, Národní Galerie), and The Harvesters. Though rooted in the legacy of calendar scenes, Bruegel’s emphasis is not on the labors that mark each season but on the atmosphere and transformation of the landscape itself.