Physiology and functional anatomy of nectarivorous birds
kolibříci; hummingbirds; hovering flight; třepotání; trávení; strdimilové; nectarivory; honeyeaters; physiology; nektarivorie; osmoregulace; adaptation; fyziologie; digestion; osmoregulation; sunbirds; vířivý let; adaptace; kystráčci
mesheuropmc: animal structures
Hummingbirds, sunbirds and a large part of honeyeaters belong to the most specialized nectarivores. During the evolution they have developed a number of adaptations in reaction to the specificity of their diet. The amount of studies focused on the adaptations connected with the digestion of nectar is not big, but is still growing. One of the characteristics of these birds is very fast and effective transport of consumed sugars across the intestinal epithelium. Furthermore they are tolerant to a very low nitrogen intake and extremely high daily intake of water. Sunbirds and honeyeaters are able to modulate the rate of water absorption in the intestine, but hummingbirds are not and they absorb almost all the consumed water. During the evolution excessive water intake together with a low concentration of salt presented in the diet led to changes in renal morphology that allows the production of an exceptionally dilute urine. The hovering flight of hummingbirds is well known and very well studied. The unique anatomy of hummingbird's wings allows the power production also during upstroke. Thanks to this hummingbirds are able to hover for a very long time and even in condition that are unsuitable for flight. Also sunbirds and honeyeaters sometimes hover during feeding. Nevertheless the mechanics of their hovering...