This box is extremely rare and very few other examples of this six-tiered form appear to have been published. Compare with an example in the Kaisendo Museum, Yamagata Prefecture included in the 1984 Tokugawa and Nezu Museum exhibition, Carved Lacquer, and illustrated in the Catalogue, no. 45. The Kaisendo box has five tiers but it is likely that it originally had six. The subject of two birds in flight amidst flowers and foliage was very popular during the Song and Yuan dynasties, and can be found most often in a circular composition such as on a dish or round box, where the bodies of the birds and their long flowing tail feathers form a circular motion. See, for example, the dish from the Tokugawa Art Museum, Nagoya, signed by the famous Yuan dynasty lacquer carver Zhang Cheng, included in the same exhibition and illustrated in the Catalogue, no. 52. A tray with a Yang Mao mark with a similar design was sold at Christie's Hong Kong, 30 May 2005, lot 1335. The boldness of the design and in particular the contrast between the sweeping deep carving and the delicately incised details is characteristic of the small group of wares carved with birds dating to the Yuan period.