Dept. of Zoology and Entomology, Univ. of Pretoria, South Africa.
Am J Physiol Regul Integr Comp Physiol. 2010 Oct;299(4):R1068-74. doi: 10.1152/ajpregu.00208.2010. Epub 2010 Aug 4.
Floral nectars of bird-pollinated plants are relatively dilute. One hypothesis proposed to explain this concerns the difficulty for birds of drinking nectar of high viscosity. We examined the effects of viscosity, separately from those of sugar concentration, on feeding by captive whitebellied sunbirds (Cinnyris talatala). Viscosities of artificial nectar (sucrose solutions ranging in concentration from 0.25 to 1.5 mol/l) were altered with Tylose, an inert polysaccharide. Food consumption was measured over 3 h, and lick frequency and duration were recorded using photodetection devices on feeding apertures too small for the bill but large enough for the extended tongue. Volumetric intake rates (ml/s) were inversely proportional to nectar viscosity, and were similar over the range of sucrose concentrations when viscosity was held constant. Sucrose intake rates (mg/s) remained the same on pure sucrose solutions, but they decreased with increasing viscosity at a constant sucrose concentration. Lick frequencies and tongue loads were reduced at high viscosities, and lick duration increased, which confirms that sunbirds take longer to ingest viscous solutions. Licking behavior was remarkably similar in birds feeding on different sucrose concentrations if viscosity was held constant. Nectar ingestion rate is determined by viscosity; however, total food intake is mainly modulated by sugar concentration. Similar effects of food viscosity have been observed in insects that suck nectar.
鸟类传粉植物的花蜜相对较稀。有一种假说解释了这一点,即鸟类很难吸食高粘度的花蜜。我们研究了粘度(从糖浓度中分离出来)对圈养的白腹太阳鸟(Cinnyris talatala)进食的影响。使用泰洛塞(一种惰性多糖)来改变人工花蜜(蔗糖浓度从 0.25 到 1.5 摩尔/升的蔗糖溶液)的粘度。在 3 小时内测量食物消耗,使用太小而无法容纳喙但足以容纳延伸舌头的进食口上的光电检测设备来记录舔舐频率和持续时间。体积摄入量(ml/s)与花蜜粘度成反比,当粘度保持恒定时,在蔗糖浓度范围内相似。在纯蔗糖溶液中,蔗糖摄入量(mg/s)保持不变,但在恒定蔗糖浓度下,随着粘度的增加而减少。高粘度时舔舐频率和舌负荷降低,舔舐持续时间增加,这证实了太阳鸟需要更长时间才能摄入粘性溶液。如果粘度保持不变,鸟类在不同蔗糖浓度下的进食行为非常相似。花蜜摄入率由粘度决定;然而,总食物摄入量主要由糖浓度调节。在吸食花蜜的昆虫中也观察到了类似的食物粘度的影响。