The Da Costa Hours is in the collection of the Pierpont Morgan library. It, like the Golf Book hours in the British Library was illuminated by Simon Bening (1483/84–1561); Belgium, Bruges, ca. 1515.
I’ve written about the May calendar image from the British Library’s Golf Book. It’s very similar in terms of motifs to this one. On the calendar page itself the Gemini twins are featured in the rondel at the base of the page. Just as in the Golf Book calendar page for May, Bening in the Da Costa Hours features a boat with greenery and musicians celebrating May 1 and the arrival of Spring.
Beyond the boaters (click for a larger image) you can see a castle, swans, and a group on horseback in the background. They too have been busy gathering the green boughs of May.