The integration of diet, physiology, and ecology of nectar-feeding birds

McWhorter, Todd J.; Lopez-Calleja, M. Victoria

doi:10.4067/s0716-078x2000000300008

Cited by 24 publications

(13 citation statements)

References 49 publications

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“…Since relationships between nectar intake rate and sugar concentration in nectar-feeding birds are power functions (López-Calleja et al, 1997;Martínez del Rio, 1999, 2000;McWhorter and López-Calleja, 2000;Martínez del Rio et al, 2001;Nicolson and Fleming, 2003), we determined the effects of temperature and individual bird (subject) on nectar intake rate using linear models of logetransformed intake and sucrose concentration data. Analysis of covariance (ANCOVA) was used on loge-transformed data to compare the slope and intercept of this relationship among experimental temperatures.…”

Section: Discussionmentioning

confidence: 99%

“…Typically, nectar-feeding birds reduce their food (hereafter 'nectar', normally the source of both energy and water in these animals) intake rate with increasing sugar concentration (López-Calleja et al, 1997;Martínez del Rio, 1999, 2000;McWhorter and López-Calleja, 2000;Martínez del Rio et al, 2001). Manipulation of sugar concentration therefore leads to a wide range of variation in the quantity of nectar (and thus water) ingested.…”

Section: Experimental Designmentioning

confidence: 99%

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Renal function in Palestine sunbirds: elimination of excess water does not constrain energy intake

McWhorter

Rio

Pinshow

et al. 2004

Journal of Experimental Biology

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SUMMARY Although the renal responses of birds to dehydration have received significant attention, the consequences of ingesting and processing large quantities of water have been less studied. Nectar-feeding birds must often deal with exceptionally high water intake rates in order to meet their high mass-specific energy demands. Birds that ingest large volumes of water may either eliminate excess water in the kidney or regulate the volume of water absorbed in the gastrointestinal tract. Because water absorption in the gastrointestinal tract of Palestine sunbirds (Nectarinia osea)decreases with increasing water ingestion rate, we predicted that glomerular filtration rate (GFR) in these birds would not be unusually high in spite of large ingested water loads. When feeding on dilute sucrose solutions, sunbirds ingested between 4 and 6 times their body mass in nectar per day, yet they were able to compensate for varying nectar energy density and increased thermoregulatory energy demands with no apparent difficulty. GFR was lower than predicted (1976.22±91.95 μl h-1), and was not exceptionally sensitive to water loading. Plasma glucose concentrations were high, and varied 1.8-fold between fasted (16.08± 0.75 mmol l-1) and fed (28.18±0.68 mmol l-1) sunbirds, but because GFR was low, glucose filtered load also remained relatively low. Essentially the entire glucose filtered load (98%) was recovered by the kidney. Renal fractional water reabsorption (FWR) decreased from 0.98 to 0.64 with increasing water intake. The ability of Palestine sunbirds to reduce the absorption of ingested water in the gastrointestinal tract may resolve the potential conflict between filtering a large excess of absorbed water in the kidney and simultaneously retaining filtered metabolites.

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Section: Discussionmentioning

confidence: 99%

Section: Experimental Designmentioning

confidence: 99%

Renal function in Palestine sunbirds: elimination of excess water does not constrain energy intake

McWhorter

Rio

Pinshow

et al. 2004

Journal of Experimental Biology

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“…Although we were unable to directly compare the transit rates of mistletoe fruit between our study species, mistletoebirds have previously demonstrated much faster transit rates of mistletoe fruit through their highly specialized intestinal tracts compared with silvereyes and honeyeaters (Keast 1958;Murphy et al 1993;French 1996;Stanley and Lill 2002;Barea 2008). We are not aware of any measurements of digesta retention time in mistletoebirds feeding on liquid diets, but it is highly likely that mistletoebirds, like many other species (Lopez-Calleja et al 1997;Levey and Martinez del Rio 1999;McWhorter and Lopez-Calleja 2000;McWhorter et al 2006;Wilson and Downs 2011), do vary retention time with energy density. A high capacity for mediated glucose uptake (not quantified in this study) might mean that mistletoebirds can meet their energy needs without an increased reliance on paracellular uptake.…”

Section: Mechanism Of Sugar Absorptionmentioning

confidence: 99%

Mistletoebirds and Xylose: Australian Frugivores Differ in Their Handling of Dietary Sugars

Napier¹,

Fleming²,

McWhorter³

2014

Physiological and Biochemical Zoology

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Carbohydrate-rich mistletoe fruits are consumed by a wide range of avian species. Small birds absorb a large portion of watersoluble nutrients, such as glucose, via the paracellular pathway. d-xylose, a pentose monosaccharide, is abundant in some nectars and mistletoe fruits consumed by birds, and it has been suggested that it is most likely absorbed via the paracellular pathway in birds. We measured apparent assimilation efficiency ( ) and * AE bioavailability (f) for d-xylose and d-and l-glucose in three frugivorous Australian bird species. Mistletoebirds, silvereyes, and singing honeyeaters showed significantly lower for d- * AE xylose than for d-glucose. Across two diet sugar concentrations, silvereyes and singing honeyeaters significantly increased f of both l-glucose (a metabolically inert isomer of d-glucose commonly used to quantify paracellular uptake) and d-xylose on the more concentrated diet, probably because of increased gut processing time. By contrast, mistletoebirds (mistletoe fruit specialists) did not vary f of either sugar with diet concentration. Mistletoebirds also showed higher f for d-xylose than l-glucose and eliminated d-xylose more slowly than silvereyes and singing honeyeaters, demonstrating differences in the handling of dietary xylose between these species. Our results suggest that d-xylose may be absorbed by both mediated and nonmediated mechanisms in mistletoebirds.

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“…Indeed, hummingbirds preferred liquid diets with lower nitrogen concentrations over more concentrated diets (M. V. López-Calleja, unpublished data). The adaptation to liquid diets, low in fiber and lipids, probably evolved together with a rapid gut transit time and high digestive efficiency that are typical of hummingbirds (Karasov, 1990;López-Calleja et al, 1997;McWhorter and López-Calleja, 2000). In general, the flow of the nectar in feeding birds is directly from proventriculus into duodenum, bypassing the gizzard altogether, whereas arthropods are diverted to the gizzard for mechanical maceration and peptic digestion (Klasing, 1998).…”

Section: Nitrogen Requirementsmentioning

confidence: 99%

“…Several studies have demonstrated that hummingbirds regulate their energy balance on a daily scale and that any energy imbalance immediately affects their behavior and body mass maintenance (Hainsworth, 1978;Wolf and Hainsworth, 1980;Calder et al, 1990; Martínez del Río and Karasov, 1990;McWhorter and López-Calleja, 2000;Fernández et al, 2002;López-Calleja and Bozinovic, 2003). Nevertheless, few studies have examined the protein balance of hummingbirds over a longer period than a daily time scale.…”

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The integration of energy and nitrogen balance in the hummingbirdSephanoides sephaniodes

Lopez-Calleja

Fernández

Bozinovic

2003

Journal of Experimental Biology

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SUMMARYFloral nectars are rich in energy but contain only traces of amino acids,and it has been hypothesized that arthropods may be an important source of energy and amino acids for hummingbirds. We studied the nitrogen requirements of hummingbirds as well as how they use small arthropods to satisfy their nitrogen and energy requirements and how organ mass varies with nitrogen intake. Non-reproductive green-backed firecrowns Sephanoides sephaniodes were maintained for 10 days on diets containing 0%, 0.96%,1.82%, 4.11% and 11.1% nitrogen (dry-matter basis). A second group of individuals were fed with varying amounts of nitrogen-free nectar supplemented with fruit flies. Finally, non-reproductive hummingbirds were captured as a control group for analysis of organ mass and size as well as fat content.The maintenance nitrogen requirement of green-backed firecrowns determined by regression was 1.42 mg N day-1, yet they required nearly 10 mg N day-1 to maintain body mass. When arthropods were available, we observed that hummingbirds required approximately 150 fruit flies to maintain body mass, which corresponds to a 5% nitrogen diet. Interestingly, when nectar was restricted (to 4 ml day-1), or was absent, arthropods alone were not able to satisfy the body mass balance requirements of hummingbirds,suggesting that arthropods are not adequate as an energy source. In the group offered an 11.1% nitrogen diet, the size and surface of the small intestine,and liver and kidney mass increased in comparison with the control group(non-reproductive field hummingbirds) or the nitrogen-free group, suggesting a nitrogen overload. Our results are in agreement with other studies showing low nitrogen requirements by nectarivores. An important point to stress is that nitrogen digestibility declined in the 11.1% nitrogen diet, which strongly supports our nitrogen absorption saturation hypothesis.

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The integration of diet, physiology, and ecology of nectar-feeding birds

Cited by 24 publications

References 49 publications

Renal function in Palestine sunbirds: elimination of excess water does not constrain energy intake

Renal function in Palestine sunbirds: elimination of excess water does not constrain energy intake

Mistletoebirds and Xylose: Australian Frugivores Differ in Their Handling of Dietary Sugars

The integration of energy and nitrogen balance in the hummingbirdSephanoides sephaniodes

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