ECOLOGICAL AND MORPHOLOGICAL CORRELATES O F PRYING BEHAVIOR IN WEAVERBIRDS (PLOCEIDAE)

Out of 33 weaver (Ploceidae) species studied carefully so far 12 have been observed to use prying actions of the bill (gaping, prizing open with the bill) i.e. they are able to open their bills forcibly against considerable resistance (Tab.). All prying species belong to the subf amily Ploceinae. Prying is used during nest building (to loosen fabric ), foraging to expose hidden food in a variety of places (rolled and c urling leaves, bark, epiphytes, flowers etc., Fig. la) as well as to m andibulate food (fruits and arthropods) and in preening. All gapers ar e also able to hold food under their foot and to coordinate movements of their bill and feet (Fig. Ib). Each species was classified with res pect to nest and habitat type (according to increasing complexity), di et (according to increasing granivory), and locomotion mode (according to a gradient from ground living to very acrobatic climbing). These 4 traits together with 3 measurements of the bill (length, depth, width ) were then statistically reduced by a principal component analysis an d the components linked to a species' ability to gape. As Fig. 2 shows prying is related to frequent hanging upside down, increasing insecti vory, forest habitat and a long bill. Consequently, as in the icterids , the most accomplished gapers are arboreal insectivorous forest speci es. In contrast to icterids, prying was neither developed by short-bil led forms nor by ground-living weaver species. Prying has aided the re markable adaptive radiation of the group.