White- and Mossy-nest Swiftlets are sister species (Chantler & Driessens 1995), being almost impossible to distinguish morphologically. However, even though their diets are also very similar (Fig. la), there does appear to be some diet separation between the two species: the average size of prey taken by the Whitenest Swiftlet in this study was significantly smaller than that taken by the Mossy-nest Swiftlet.