According to Buijs in Lyon 1991, p.30, there was once a whole other putto to the main figure's right who was painted out. Also some birds were changed--ones that were utterly finished to the last detail were painted out and replaced by others.

COPIES AND VARIANTS:
copper, 68 x 86, very primitive also, sold Cologne (Kunsthaus 10.xi.76 #1433); also quite bad is one sold London (Christie's 26.vi.64 #133, on copper, 25 x 35 in.). Another truly awful one sold Fieris (?) 7.vii.26 #17; another was with G. Cramer in The Hague at some point; a really dreadful one on copper, 54 x 85, in Dublin, National Gallery of Ireland, and another bad one in collection Ten Cate, Almelo, in 1975. Ste-Gudule sale, Brussels, March 27, 1912 (copper, 66 x 87 cm); Dorotheum, Vienna, March 18-21 1912 (canvas, 58 x 71 cm); Störi, Zurich, December 5, 1924; Fievez, Brussels, July 7-8, 1926 (copper, 31 x 42 cm); Lepke, Berlin, April 1911 (panel, 57 x 97 cm); Sotheby's London, June 26, 1964 (copper, 63.5 x 88.9 cm); Christie's London, December 11, 1981 (38.6 x 56.5 cm); Christie's London, December 13, 1929 (panel, 55.9 x 80 cm). These are all different paintings, and all are of varying degrees of awfulness. Why so many very bad copies here? I think it's mostly the figure painters who are bad, I can't tell so much about the birds.
There's even one with no figure!--just the birds have been copied [id on back of RKD photo only as Wetzlar].
A clearly better painting is the one sold Christie's London 11.xii.87 #67A: on panel, 45.5 x 82.5 cm. The ground here seems never to have been finished. Ertz attributes this to Jan the Younger around 1630 (before vBalen died). I don't get this picture, the figures seem to be in OK shape but the ground is either unfinished or damaged (it's certainly damaged) or both. Perhaps the figures were repainted later?