From the Reise der österreichischen Fregatte Novara [...] Zoologischer Theil, A. Pelzeln, "Vögel":

"In addition to two birds, an egg of this species was also sent. The latter is finely mottled reddish-brown with only a few larger spots of the latter colour towards the opaque end. The colouration of this egg is very reminiscent of that of some eggs of Tinnunculus alaudarius, a similarity already pointed out by Orbigny (Voyage Amer. Mer. 62)" (p. 6)