RUMMEL, T. D.; KIMBERLY, D. J.; POWERS, D. R.; MCWHORTER, T. J.; George Fox University; George Fox University; George Fox University; Univ. of Wisconsin, Madison: Functional and Morphological Comparison of Hummingbird and Sunbird Digestive Tracts

A morphological comparison of the Palestine Sunbird (Nectarinia osea) and Rufus Hummingbird (Selasphorus rufus) gastro-intestinal tracts illustrates structural differences in the proventriculus and gizzard despite similar nectarivorous dietary habits. The Sunbird proventricular-gizzard alignment is more linear than the new-world counterpart Hummingbird with its juxtapositional arrangement. The acid-secreting proventriculi are equivalent in diameter with a larger lumenal channel in the Sunbird. The Hummingbird mucosa is composed of long (0.58 mm), nonbranched villi with an intervillar space of 20 mm and anchored to a thin gut wall (25 mm). The Sunbird has a thicker gut wall (70 mm) and a compartmentized, labyrinthian mucosa. The Hummingbird absorptive surface is composed of simple columnar epithelium with a prominent brush-border (microvilli). The septal cuboidal epithelium of the Sunbird has no apparent microvilli but an increase of total surface exposure. Minimal goblet cells are seen compared to the scattered mucus cells of the Hummingbird. Both birds have a cuticle (koilin) protecting the lumenal surface of the gizzard and abundant mucosal glands in the crypts of the epithelium. The Hummingbird has a �cap� of simple columnar cells between the cuticle and the tightly compacted, cuboidal columns of mucosa. A more prominent muscularis externa. (0.55 mm) is found in the Hummingbird compared to the Sunbird (0.32 mm).