The traditional labors of September shown in books of hours are harvesting and treading grapes in warmer regions and ploughing and sowing (and sometimes, threshing) in colder climates. In this detail of the September calendar image from the Morgan Library’s Da Costa Hours (MS M.399, fol. 10v), in the foreground a man ploughs with the aid of two horses. Behind him another man is sowing seeds by casting. The seeds are probably winter wheat, and there are more of them in the basket of grain resting on the ground.
Behind him and to the left, a man with a stick is knocking down nuts for the swine below the trees; this is typically the labor for November, but as an actual activity it took place as soon as nuts began to ripen.
The birds eagerly gobbling the seeds are probably European crows, sometimes called Carrion crows, or Corvus corone. Crows in medieval bestiaries are associated with longevity, and warning humans of ambushes. Pliny mentions crows’ habit of dropping nuts on rocks to crack them. Actual crows today do in fact make a racket when the see predatory birds or animals, and that includes humans, and Carrion crows really do drop nuts on rocks and other hard surfaces, like paved roads and sidewalks, to crack them.