The Integration of Osmoregulation and Energy Balance in Hummingbirds

Beuchat, Carol A.; Calder, William A.; Braun, Eldon J.

doi:10.1086/physzool.63.6.30152633

Cited by 61 publications

(66 citation statements)

References 38 publications

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“…Aside from the fascination of bird-flower associations, nectar-feeding birds are excellent models for ecophysiological research because their energetics and water turnover are extreme and inseparable (Beuchat et al 1990;Martı´nez del Rio et al 2001). They are generally small, and consequently have high mass-specific metabolic rates: hummingbirds are the smallest endotherms and their hovering flight is especially expensive.…”

Section: Nectar Feeding Is Widespread In Birdsmentioning

confidence: 99%

“…In terms of studying digestive physiology, they eat sugar solutions, a deceptively simple food. And finally, these sugar solutions are dilute, so that water fluxes through the bodies of avian nectarivores may be extraordinarily high (Beuchat et al 1990;Martı´nez del Rio et al 2001;Nicolson and Fleming 2003).…”

Section: Nectar Feeding Is Widespread In Birdsmentioning

confidence: 99%

“…In fact, sucrose digestion involves the additional step of sucrose hydrolysis. Secondly, the osmolality of sucrose solutions is around half that of energy-equivalent hexose mixtures (Beuchat et al 1990, Nicolson 2002: if the rate of delivery of food from crop to intestine is mediated by osmolality, then sucrose might be processed faster than hexose mixtures, but this is not the case (Martı´nez del Rio 1990b). The preference switch to hexoses on dilute diets, however, may be linked with the greater osmolality of hexose solutions.…”

Section: Sugarsmentioning

confidence: 99%

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Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions

2003

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Abstract. Nectarivory has evolved many times in birds: although best known in hummingbirds, sunbirds and honeyeaters, it also occurs on an opportunistic basis in a varied assortment of birds. We present a phylogenetic analysis of the distribution of nectarivory in birds. Specialised avian nectarivores are generally small, with an energetic lifestyle and high metabolic rates. Their high degree of dependence on nectar as a food source has led to convergence in morphological, physiological and behavioural adaptations. We examine the constituents of nectar which are most important to bird consumers, and how the birds deal with them in terms of physiology and behaviour. There are still unanswered questions: for example, the dichotomy between sucrose-rich nectars in hummingbirdpollinated plants and predominantly hexose-rich nectars in sunbird-pollinated plants appears to have little to do with bird physiologies and may rather reflect patterns of nectar secretion.

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Section: Nectar Feeding Is Widespread In Birdsmentioning

confidence: 99%

Section: Nectar Feeding Is Widespread In Birdsmentioning

confidence: 99%

Section: Sugarsmentioning

confidence: 99%

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Nectar as food for birds: the physiological consequences of drinking dilute sugar solutions

2003

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“…Previous suggestions that, even under conditions of water deficiency, nectarivores cannot produce urine of higher osmolality than plasma (≈ 350 mOsmol/kg H 2 O) may be accurate for some hummingbirds (Beuchat et al 1990;Lotz and Martínez del Rio 2004). However, under extreme conditions, sunbirds certainly are capable of producing relatively concentrated urine (sunbirds: 499 mOsmol/kg H 2 O; present study), while honeyeaters excrete somewhat less concentrated excreta (368 mOsmol/kg H 2 O; present study).…”

Section: No-choice Experimentsmentioning

confidence: 98%

“…The ability to adjust volumetric intake to maintain a steady energy intake is extremely important for these birds in view of the wide range of nectar concentrations and associated water loads (Fleming et al 2004a;Nicolson and Fleming 2003a). Electrolyte balance is potentially a major problem for birds that process several times their body mass in water each day (Beuchat et al 1990;Martínez del Rio et al 2001;McWhorter and Martínez del Rio 1999;Nicolson and Fleming 2003a). Eight species of hummingbird feeding on dilute nectars were shown to eliminate excess water in chronic diuresis: these hummingbirds conserved solutes by reducing their urine osmolality to a fifth of plasma levels .…”

Section: Introductionmentioning

confidence: 99%

Salt intake and regulation in two passerine nectar drinkers: white-bellied sunbirds and New Holland honeyeaters

2012

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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 whitebellied 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 to 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 2 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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