Avian nectarivores face the dilemma of having to conserve salts while consuming large volumes of a dilute, electrolyte-deficient diet. This study evaluates the responses to salt solutions and the regulation of salt intake in white-bellied sunbirds (Cinnyris talatala) and New Holland honeyeaters (Phylidonyris novaehollandiae). Birds were first offered a choice of four sucrose diets, containing no salt or 25, 50 or 75 mM NaCl. The experiment was repeated using five sucrose concentrations (0.075-0.63 M) as the base solution. Both species ingested similar amounts of all diets when fed the concentrated base solutions. However, when birds had to increase their intake to obtain enough energy on the dilute sucrose diets, there was a general avoidance of the higher salt concentrations. Through this diet switching, birds maintained constant intakes of both sucrose and sodium; the latter may contribute to absorption of their sugar diets. A second, no-choice experiment was designed to elucidate the renal concentrating abilities of these two nectarivores, by feeding them 0.63 M sucrose containing 5-200 mM NaCl over a 4-h trial. In both species, cloacal fluid osmolalities increased with diet NaCl concentration, but honeyeaters tended to retain ingested Na+, while sunbirds excreted it. Comparison of Na+ and K+ concentrations in ureteral urine and cloacal fluid showed that K+, but not Na+, was reabsorbed in the lower intestine of both species. The kidneys of sunbirds and honeyeaters, like those of hummingbirds, are well suited to diluting urine; however, they also appear to concentrate urine efficiently when necessary.
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机译:鸟类油桃面临的困境是必须在食用大量稀薄的,缺乏电解质的饮食的同时保存盐分。这项研究评估了白腹太阳鸟(Cinnyris talatala)和新荷兰蜜食者(Phylidonyris novaehollandiae)对盐溶液的响应和盐摄入的调节。首先为鸟类提供四种蔗糖饮食选择,其中不含盐或25、50或75 mM NaCl。使用五种浓度的蔗糖(0.075-0.63 M)作为基础溶液重复实验。当饲喂浓缩的基本溶液时,这两种物种都摄入了相似量的所有饮食。但是,当家禽不得不增加摄入量以在稀蔗糖饮食中获得足够的能量时,通常可以避免较高的盐浓度。通过这种饮食转换,鸟类可以保持恒定的蔗糖和钠摄入量。后者可能有助于吸收他们的糖饮食。第二个非选择实验旨在通过在4小时的试验中向它们喂食含5-200 mM NaCl的0.63 M蔗糖来阐明这两种油桃的肾脏浓缩能力。在这两个物种中,泄殖腔的重量摩尔渗透压浓度均随日粮NaCl浓度的增加而增加,但食蜜者倾向于保留摄入的Na +,而太阳鸟则将其排出。输尿管尿液和泄殖腔液中Na +和K +浓度的比较表明,这两种物种的小肠均会重新吸收K +,而不吸收Na +。像蜂鸟一样,太阳鸟和食蜜者的肾脏非常适合稀释尿液。但是,它们在必要时也可以有效地浓缩尿液。
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