Whitebellied sunbirds (<Emphasis Type="Italic">Nectarinia talatala</Emphasis>, Nectariniidae) do not prefer artificial nectar containing amino acids

Amino acids are the most abundant class of compounds in nectar after sugars. Like its sugar concentration, the amino acid concentration of nectar has been linked to pollinator type, and it has been suggested that amino acid concentrations are high in the floral nectars of plant species pollinated by passerine birds compared to those pollinated by hummingbirds. We investigated the feeding response of whitebellied sunbirds (Nectarinia talatala) to the inclusion of amino acids in artificial nectar (0.63 M sucrose solution). The response to asparagine, glutamine, phenylalanine, proline, serine and valine, amino acids commonly found in floral nectars, was tested individually and using a mixture of all six amino acids, at two different concentrations (2 and 15 mM). Sunbirds showed no significant preference for amino acids in nectar, or avoided them, especially at the higher concentration. We discuss these findings in the light of the nitrogen requirements of nectarivorous birds and data on amino acids in floral nectars.     

FLORAL NECTAR SUGAR COMPOSITION AND POLLINATOR TYPE AMONG NEW WORLD GENERA IN TRIBE ANTIRRHINEAE (SCROPHULARIACEAE)

The floral nectar sugar compositions of 20 New World species from 10 genera and of five interspecific hybrids in tribe Antirrhineae have been analyzed using high-performance liquid chromatography. Species are pollinated by short-tongued bees, long-tongued bees, and hummingbirds. Ornithophily represents the derived condition in the tribe and has arisen independently in subtribes Maurandyinae and Gambeliinae. All nectars analyzed are sucrose-dominant or -rich, except for the hexose-rich nectar of Mohavea breviflora. Despite the predominance of sucrose, floral nectar sugars from species pollinated by different pollen vectors have characteristic constituents. Nectar sugars from flowers visited by hummingbirds average 76.2% sucrose and have compositions remarkably similar to hummingbird nectars analyzed in previous studies of unrelated species. Long-tongued bee nectars average 87% sucrose and differ from shorttongued bee nectars which have the lowest mean sucrose percentage (40.2%). The association of sugar constituent types and principal pollinators is concordant with previous data and supports hypotheses concerning pollinator preferences and the adaptive significance of certain nectar sugar compositions. Within this adaptive framework, phylogenetic constraint is also operative and may explain the predominance of sucrose in nectar sugars, similarities in sugar composition among hummingbird nectars in subtribes Maurandyinae and Gambeliinae, and the similarity of nectar from Galvezia leucantha (long-tongued bee-pollinated) to hummingbird-pollinated species also in subtribe Gambeliinae.     

Sugar and amino acid composition of ant‐attended nectar and honeydew sources from an Australian rainforest

Abstract Ants (Hymenoptera: Formicidae) consume a broad spectrum of liquid food sources including nectar and honeydew, which play a key role in their diet especially in tropical forests. This study compares carbohydrates and amino acids from a representative spectrum of liquid sources used by ants in the canopy and understorey of a tropical rainforest in northern Queensland, Australia. Eighteen floral nectars, 16 extrafloral nectars, two wound sap and four homopteran honeydew sources were analysed using high performance liquid chromatography. Wounds comprised flower abscission scars on Normanbya normanbyi L. H. Bailey and bitemarks on Cardwellia sublimis F. Muell. where ants were actively involved in wounding. Discriminant analysis was performed to model differences between food sources in sugar and amino acid concentration and composition. All characteristics varied significantly among plant species. Honeydew contained a broader spectrum of sugars (including melezitose, raffinose, melibiose, lactose and maltose) than nectar (sucrose, glucose, fructose), but certain extrafloral nectars had similar amino acid profiles and, like honeydew sources, were often monopolized by ants. Most common amino acids across the sources were proline, alanine and threonine among 17 α‐amino acids identified. Interspecific variability concealed characteristic differences in sugar and amino acid parameters between nectar, honeydew and wound sap across all plants, but these types differed significantly when found on the same plant. Among all sources studied, only a few flower nectars were naturally not consumed by ants and they were significantly less attended than sugar controls in feeding trials. These nectars did not differ in sugars and amino acids from ant‐attended flower nectars, suggesting the activity of repellents. Apart from these exceptions, variability in amino acids and carbohydrates is proposed to play a key role in ant preferences and nutrition.     

Sugar preferences, absorption efficiency and water influx in a Neotropical nectarivorous passerine, the Bananaquit (Coereba flaveola)

Nectarivory has evolved repeatedly in a number of unrelated bird taxa throughout the world and nectar feeding birds, regardless of their taxonomic affiliation, display convergent foraging and food processing adaptations that allow them to subsist on weak sugar solutions. However, phylogeny influences sugar type preferences of nectarivores. We investigated sugar preferences, assimilation efficiency and water flux in a Neotropical honeycreeper, the Bananaquit (Coereba flaveola; Coerebidae), a member of a radiation of tanagers and finches. Bananaquits showed no preference for nearly equicaloric (25% w/v) sucrose, glucose, fructose or glucose-fructose mixtures in pair-wise choice tests. In agreement with this lack of preference, they were equally efficient at absorbing sucrose and both hexoses. Apparent assimilation efficiency of these sugars was around 97.5%. In pair-wise tests, Bananaquits displayed a strong preference for the most concentrated sucrose solution when the lowest concentration ranged from 276 to 522 mM. Between 522 and 1120 mM sucrose solution concentrations, Bananaquits were able to adjust their volumetric food intake in order to maintain a constant energy intake. At solution concentration of 276 mM, birds could not maintain their rate of energy intake by increasing food consumption enough. We consider that at low sugar concentrations, Bananaquits faced a physiological constraint; they were unable to process food at a fast enough rate to meet their energy needs. We also explored the possibility that dilute nectars might be essential to sustain high water needs of Bananaquits by allowing them to control osmolarity of the food. Between 276 and 1120 mM sucrose solution concentrations, average amount of free water drunk by Bananaquits was independent of food concentration. They drank very little supplementary water and did not effectively dilute concentrated nectars. The evidence suggests that water bulk of dilute nectars is a burden to Bananaquits.     

The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar‐feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar‐feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte‐free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte‐free food they produced excreta containing less than 0.5 mM l^?1 each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l^?1 sucrose) contained more than 35 mM l^?1 of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

The foraging behaviour of Australian honeyeaters: a review and some comparisons with hummingbirds

The foraging behaviour of Australian honeyeaters is reviewed in terms of diet, foraging selectivity, foraging flight mode, quality and quantity of nectar encountered per flower, flower densities encountered and effect of predation. At the same time comparisons are made between honeyeaters and hummingbirds. These two groups of birds are superficially similar. Both feed on nectar and insects. Both tend to have long curved bills and tongues adapted for removal of nectar from flowers. Both tend to feed at long, red flowers. However, on close inspection, honeyeaters and hummingbirds are quite dissimilar. For example, many honeyeaters include fruit in their diets. Hummingbirds almost never eat fruit. Honeyeaters appear to be considerably less nectarivorous and more insectivorous than hummingbirds. Honeyeaters are, for the most part, larger than hummingbirds and they usually perch while feeding whereas hummingbirds usually hover. Honeyeaters but not hummingbirds often flock while feeding. Predation appears to be considerably more important for honeyeaters than for hummingbirds. Territorial defense of flowers seems common in hummingbirds but uncommon in honeyeaters. These differences are discussed in detail and explanations are offered for them wherever possible.     

Hummingbirds fuel hovering flight with newly ingested sugar

We sought to characterize the ability of hummingbirds to fuel their energetically expensive hovering flight using dietary sugar by a combination of respirometry and stable carbon isotope techniques. Broadtailed hummingbirds (Selasphorus platycercus) were maintained on a diet containing beet sugar with an isotopic composition characteristic of C3 plants. Hummingbirds were fasted and then offered a solution containing cane sugar with an isotopic composition characteristic of C4 plants. By monitoring the rates of CO2 production and O2 consumption, as well as the stable carbon isotope composition of expired CO2, we were able to estimate the relative contributions of carbohydrate and fat, as well as the absolute rate at which dietary sucrose was oxidized during hovering. The combination of respirometry and carbon isotope analysis revealed that hummingbirds initially oxidized endogenous fat following a fast and then progressively oxidized proportionately more carbohydrates. The contribution from dietary sources increased with each feeding bout, and by 20 min after the first meal, dietary sugar supported approximately 74% of hovering metabolism. The ability of hummingbirds to satisfy the energetic requirements of hovering flight mainly with recently ingested sugar is unique among vertebrates. Our finding provides an example of evolutionary convergence in physiological and biochemical traits among unrelated nectar-feeding animals.     

Foraging behavior adjustments related to changes in nectar sugar concentration in phyllostomid bats

Nectar-feeding bats regulate their food ingestion in response to changes in sugar concentration as a way to achieve a constant energy intake. However, their digestive capability to assimilate sugars can limit their total energy intake, particularly when sugar concentration in nectar is low. Our experimental study evaluated the effect that changes in sugar concentration of nectar have on the foraging behavior of the nectar-feeding bats Glossophaga soricina and Leptonycteris yerbabuenae in captivity. We measured foraging behavior and food intake when bats fed at different concentrations of sucrose (5, 15, 25 and 35%wt/vol.). To compensate for low-energy intake, both bat species reduced their flight time, and increased feeding time when sugar concentration decreased. Our results suggest that nectar-feeding bats in nature confront two scenarios with complementary ecological effects: 1) bats feeding on dilute nectars (i.e. ≤15%wt/vol.) should increase the number of flowers visited per night enhancing pollination, and 2) bats feeding on concentrated nectars could spend more time flying, including long- and short-distance-flights increasing food patch exploration for use during subsequent nights, and thus enhancing plant gene flow. Further studies on foraging behavior of nectarivorous bats under natural conditions are necessary to corroborate these hypotheses.     

The role of size and dominance in the feeding behaviour of coexisting hummingbirds

Interspecific competition can strongly influence community structure and limit the distribution and abundance of species. One of the main factors that determine hummingbird community structure is competition for food. The temporal and spatial distribution of nectar has a strong impact on hummingbird assemblages, shaping foraging niches according to hummingbird dominance and foraging strategy. We investigated whether body size and the degree of aggressive dominance influence feeding behaviour of hummingbirds in a temperate forest in northwestern Mexico (El Palmito, Mexico) when winter migrant hummingbirds are present in the community. First, we determined the dominance status of hummingbirds and evaluated the relationship between dominance and body mass, wing disc loading and migratory status. Secondly, we determined how hummingbird species used plant species differently. Thirdly, we examined whether the most dominant hummingbird species defended floral patches with more energy and/or with a larger number of flowers. At each flower patch, hummingbird species, number of hummingbird interactions, feeding time and number of flowers present were recorded. The total number of calories available within each floral patch was also determined. Our results demonstrate that the dominance hierarchy of 13 hummingbird species (migratory and resident) was correlated with body size but not wing disc loading, and that members of the hummingbird community showed a clear separation in resource use (by plant species). Hummingbirds at the top of the dominance hierarchy defended and fed on the best flower patches, defined by the quantity of calories available. Hence, the feeding behaviour of hummingbirds at El Palmito depends on the abundance of plant species used by hummingbirds and on the amount of energy available from each flower patch. Thus, hummingbird body size, aggressive dominance and defence of quality flower patches determines niche partitioning among species.     

On the temperature-dependency of optimal nectar concentrations for birds.

In addition to the crucial need for energy balance, the metabolically-intense hummingbirds must maintain osmotic homeostasis by regulating salt and fluid balance. Hypothetically, flowers which have coevolved with pollination by hummingbirds could provide both energy and water balance simultaneously if they produced nectars of appropriate concentrations which depend upon environmental temperature. To the extent that this has not completely adjusted, hummingbirds exposed to cold and hot extremes in temperature will have problems of water excess or deficiency, respectively.     

The ability of rufous hummingbirds Selasphorus rufus to dilute and concentrate urine

Most terrestrial animals face the challenge of having to conserve water in a desiccating environment. Not surprisingly, the ability to produce concentrated urine has been relatively well studied in birds. Nectar-feeding birds are unusual among terrestrial animals in that they often ingest and excrete prodigious water volumes to obtain adequate energy. Thus, they confront the unusual challenge of having to conserve electrolytes. The diluting abilities of birds and the renal mechanisms that may correlate with them have been relatively neglected. To elucidate diluting and concentrating abilities in nectar-feeding birds, we fed rufous hummingbirds Selasphorus rufus an electrolyte-free nectar and a nectar containing a range of NaCl concentrations. Hummingbirds had a spectacular (and possibly unique) diluting ability: when fed on electrolyte-free food they produced excreta containing less than 0.5 mM l⁻¹ each of sodium and potassium. Hummingbirds also had a poor concentrating ability, retaining sodium and chloride when their food (0.632 M l⁻¹ sucrose) contained more than 35 mM l⁻¹ of NaCl. The kidneys of hummingbirds do not appear to be suited for concentrating urine, and possibly contain structural features that give them a unique diluting ability compared with those of birds that do not feed on nectar.     

Sugar preferences and digestive efficiency in an opportunistic avian nectarivore, the Dark-capped Bulbul Pycnonotus tricolor

It has recently been recognized that flowers pollinated by generalist opportunistic nectarivores tend to have different nectar properties to those pollinated by specialist nectarivores (including both hummingbirds and specialist passerines). While renewed interest in specialist avian nectarivore sugar preferences and digestive physiology has helped explain the concentrated sucrose-dominated nectar of plants they feed on, there has been little progress in understanding why generalist or occasional nectar-feeding birds tend to be associated with flowers that have dilute hexose-dominated nectar. We examined sugar preferences and assimilation efficiencies over a range of concentrations, and concentration preferences, in Dark-capped Bulbuls Pycnonotus tricolor, one of the more common occasional avian nectarivores in southern Africa. Dark-capped Bulbuls showed significant preference for hexose sugar solutions, irrespective of concentration, when given a choice between hexose and sucrose solutions in equicaloric pair-wise choice tests conducted at five different concentrations (5–25%). This contrasts with results from specialist nectarivore groups which generally show a significant concentration-dependant switch in preference from hexose at low concentrations to sucrose at high concentrations for equicaloric solutions. In addition, Dark-capped Bulbuls showed an unusual lack of preference for solutions of higher sugar concentration when simultaneously offered four solutions varying in concentration from 10 to 25%. Dark-capped bulbuls also showed a unique effect of concentration on sugar assimilation efficiency, assimilating relatively more energy on 5% diets than on 25% diets. Although able to assimilate sucrose effectively, assimilation rates of hexose sugars were marginally higher. These results shed new light on pollination systems involving occasional nectarivores and, in particular, help to explain the prevalence of low concentration hexose-dominated nectars in flowers pollinated by these birds.     

Does gut function limit hummingbird food intake?

Many nectar-feeding bird species decrease food intake when sugar concentration in food is increased. This feeding response can be explained by two alternative hypotheses: compensatory feeding and physiological constraint. The compensatory feeding hypothesis predicts that if birds vary intake to maintain a constant energy intake to match energy expenditures, then they should increase intake when expenditures are increased. Broad-tailed hummingbirds were presented with sucrose solutions at four concentrations (292, 584, 876, and 1,168 mmol L(-1)) and exposed to two environmental temperatures (10 degrees and 22 degrees C). Birds decreased volumetric food intake in response to sugar concentration. However, when they were exposed to a relatively sudden drop in environmental temperature and, hence, to an acute increase in thermoregulatory energy expenditures, they did not increase their rate of energy consumption and lost mass. These results support the existence of a physiological constraint on feeding intake. A simple chemical reactor model based on intestinal morphology and in vitro measurements of sucrose hydrolysis predicted observed intake rates closely. This model suggests that intestinal sucrose hydrolysis rates were near maximal and, thus, may have imposed limits to sugar assimilation. Although sugar assimilation was high (95%), the proportions of excreted sucrose, glucose, and fructose found in excreta differed significantly. The monosaccharides glucose and fructose were about eight and three times more abundant than sucrose, respectively. Broad-tailed hummingbirds are small high-altitude endotherms that face unpredictable weather and the energetic expense of premigratory fattening. Digestive processes have the potential to impose severe challenges to their energy budgets.     

COMPETITION BETWEEN HERMIT HUMMINGBIRDS PHAETHORNINAE AND INSECTS FOR NECTAR IN A COSTA RICAN RAIN FOREST

Hummingbirds in the tropical rainforests of southwestern Costa Rica face intense competition from stingless bees Trigona that steal nectar from hummingbird flowers. Here we document both interference and exploitative competition between bees and hummingbirds at scarlet, hummingbird pollinated flowers of Passiflora vitifolia. Aggressive stingless bees prevented Long-tailed Hermit Hummingbirds Phaethornis superciliosus from feeding at nearly one-third of the passion flowers approached. In exclusion experiments, bees and hummingbirds each removed most of the nectar from treated flowers. Experimental exclusion of bees also increased hummingbird use of both natural and artificial flowers.     

Selective choice of sucrose solution concentration by the hovering hawk mothMacroglossum stellatarum

To determine the preference of the hovering hawk mothMacroglossum stellatarum for different sugar concentrations, the foraging behavior of adults were analyzed under laboratory conditions. Six sucrose concentrations (range, 10–60%, w/w) were simultaneously offered in six artificial ab libitum feeders. The number of feeding bouts and the duration of each visit were automatically recorded and stored in a computer. Results showed that the frequency of visits to the feeders did not vary among the different solutions offered, but the gathered volume by the group attained a maximum at between 20 and 50% (w/w). Moths invested more time in front of the feeder with the more concentrated sugar solutions. It was assumed that factors different from maximizing energy intake, such as water balance and viscosity of concentrated nectars, have to be considered in order to understand the observed patterns of nectar choice.     

Energy regulation by traplining hummingbirds

1. A published model of constant diurnal energy accumulation by territorial hummingbirds does not accurately reflect the temporal distribution of feeding behaviour of traplining hummingbirds, Phaethornis longirostris (Long-Tailed Hermit Hummingbirds).
2. In an enclosure study, gross nectar intake by P . longirostris decreased through the day, mirroring nectar production rates in its natural food-flowers and mimicking its natural foraging patterns.
3. Using a simulation model, the energetic consequences of constant and decreasing net energy intake rates for traplining hummingbirds are compared.
4. Given natural patterns of nectar production, model birds with decreasing diurnal net intake rates met their energetic needs with fewer flowers than those with constant net intake, and spent less time foraging.
5. It is concluded that P . longirostris do not satisfy the physiological assumptions of the published model, and that in this way they are different from the territorial species on which the model has previously been tested.     

Hummingbird avoidance of nectar-robbed plants: spatial location or visual cues

Broad-tailed and rufous hummingbirds avoid plants and flowers that have recently been visited by nectar-robbing bees. However, the cues the hummingbirds use to make such choices are not known. To determine the proximate cues hummingbirds use to avoid visiting nectar-robbed plants, I conducted multiple field experiments and one aviary study using the nectar-robbed, hummingbird-pollinated plant Ipomopsis aggregata . In the first field experiment, free-flying hummingbirds were presented with plants in which I manipulated nectar volume and the presence of nectar-robber holes. Hummingbirds visited significantly more plants with nectar and probed more available flowers on those plants, regardless of the presence of nectar-robber holes. Thus, I hypothesized that hummingbirds may avoid robbed plants based on their spatial memory of unrewarding plants and/or visual cues that nectar absence provides. In an aviary study, I removed spatial cues by re-randomizing the position of plants after each hummingbird-foraging bout, but hummingbirds still selected plants with nectar. Nectar may provide a visual cue in I. aggregata flowers because corollas are translucent, and nectar is visible through the side of the corolla. To determine if hummingbirds use this visual cue to avoid plants with no nectar, I masked corolla translucence in a field study by painting flowers with acrylic paint. Hummingbirds still visited significantly more plants with nectar and probed more flowers on those plants, whether or not the corollas were painted. These results suggest that hummingbirds use nectar as a proximate cue to locate and avoid non-rewarding, nectar-robbed plants, even in the absence of spatial cues and simple visual cues.     

Hummingbird color preference within a natural hybrid population of Mimulus aurantiacus (Phrymaceae)

Hummingbird flowers are typically red in color but the reasons for this are not well understood. Relatively few studies have examined hummingbird flower color preferences under natural conditions in which flower color varies within a species. We recorded hummingbird visitation rates to flowers that vary in color from yellow to red in a natural hybrid population between red‐ and yellow‐flowered Mimulus aurantiacus subspecies. We also examined whether there were any correlations between color and flower size or nectar content. Finally, we reviewed the literature on hummingbird color choice tests using feeders and flowers. There were no correlations in this population between flower color and flower size, nectar volume, or sugar concentration. Nevertheless, hummingbirds undervisited the two most yellow color classes, overvisited orange flowers, and visited the two most red color classes in proportion to their frequency in the population. While Hummingbirds preferred flowers expressing red pigments to those that did not, the flowers with the most red hue were not the most attractive, as has been observed in similar studies with other species of Mimulus. While feeder studies generally fail to show hummingbird preference for red, all studies using flowers, including those that control all floral traits other than color, find consistent preference for red. Experiments are suggested that might help disentangle hypotheses for why hummingbirds exhibit this preference.     

Wintering hummingbirds in Alabama and Florida: species diversity, sex and age ratios, and site fidelity

ABSTRACT Over the past several decades, there have been numerous reports of hummingbirds wintering in the southeastern United States. However, little is known about the species present and their relative abundance. From November 1998 to March 2008, we examined the species diversity, sex and age ratios, and site fidelity of hummingbirds wintering in southern Alabama and northern Florida. We captured and banded 1598 individuals representing 10 species, and the most frequently captured species were Rufous Hummingbirds (Selasphorus rufus; 51.6%), Ruby‐throated Hummingbirds (Archilochus colubris; 23.5%), and Black‐chinned Hummingbirds (Archilochus alexandri; 16.9%). Other species captured included Buff‐bellied Hummingbirds (Amazilia yucatanensis), Calliope Hummingbirds (Stellula calliope), Allen's Hummingbirds (Selasphorus sasin), Broad‐tailed Hummingbirds (Selasphorus platycercus), Broad‐billed Hummingbirds (Cynanthus latirostris), Anna's Hummingbirds (Calypte anna), and Costa's Hummingbirds (Calypte costae). Most hummingbirds (71.8%) were captured in December and January. For most species, sex ratios were male‐biased for juveniles and female‐biased for adults, indicating possible differential mortality. Of 1598 hummingbirds captured, 144 representing five species returned to the same wintering location at least once. Female Rufous Hummingbirds (20.4% of individuals captured) exhibited the greatest site fidelity. Recaptures of banded Rufous Hummingbirds in autumn and early winter revealed that some individuals moved south into Alabama or Florida from Tennessee, northern Georgia, and northern Louisiana. Same‐season recaptures of banded Rufous Hummingbirds suggest that their spring migration route is west along the Gulf Coast. Our results suggest that Alabama and Florida are viable overwintering areas for several species of hummingbirds, with numbers of species and individuals higher than previously recognized. However, more study is needed to confirm migration routes and to determine if Ruby‐throated Hummingbirds wintering in our study area are year‐round residents or migrants.     

Preference of cabbage white butterflies and honey bees for nectar that contains amino acids

Summary Amino acids occur in most floral nectars but their role in pollinator attraction is relatively unstudied. Nectars of butterfly-pollinated flower tend to have higher concentrations of amino acids than do flowers pollinated by bees and many other animals, suggesting that amino acids are important attractants of butterflies to flowers. In order to determine whether amino acids are important in attracting butterflies and bees, we tested the preference of cabbage white butterflies (Pieris rapae) and honey bees (Apis mellifera) by allowing them to feed from artificial flowers containing sugar-only or sugar-amino acid mimics ofLantana camara nectar. Honey bees and female cabbage white butterflies consumed more sugar-amino acid nectar than sugar-only nectar. In addition, female cabbage white butterflies visited artificial flowers containing sugar-amino acid nectars more frequently than flowers containing sugar-only nectars; honey bees spent more time consuming the sugar-amino acid nectar. Male cabbage white butterflies did not discriminate between the two nectars. These results support the hypothesis that the amino acids of nectar contribute to pollinator attraction and/or feeding.