It is rather unusual to find a flask of such small size. Larger flasks are known with similar decoration, these are modelled on early Ming prototypes. For larger flasks of related design compare the blue and white flask with a Yongzheng mark in the Palace Museum, Beijing illustrated in Blue and White Porcelain with Underglazed Red (III), The Complete Collection of Treasures of the Palace Museum, Hong Kong, 2000, pl. 97. Another example decorated on yellow-enamelled ground, is illustrated by J. Ayers, The Baur Collection, 1969, vol. IV, no. A573.
Compare this example with the Ming dynasty prototype of early 15th century date decorated with a single bird perched on a branch on each side in the Percival David Foundation, illustrated by R. Scott, Percival David Foundation of Chinese Art: A Guide to the Collection, p. 73, no.61, where the author notes the derivation of this shape from Syrian glass.