Bee food : the chemistry and nutritional value of nectar, pollen and mixtures of the two

Bees are herbivorous insects, consuming nectar and pollen throughout their life cycles. This paper is a brief review of the chemistry of these two floral resources and the implications for bee nutrition. Nectar is primarily an energy source, but in addition to sugars contains various minor constituents that may, directly or indirectly, have nutritional significance. Pollen provides bees with the protein, lipids, vitamins and minerals that are essential for larval rearing. Chemical analyses of pollen have tended to focus on the protein component of bee-collected pollens as an index of nutritional quality. However, the substantial nectar content of such samples (~ 50% dry mass) should not be ignored, especially in view of current interest in measuring the nutritional quality of floral resources for bees.http://www.bioone.org/loi/afzoab201

Brood comb as a humidity buffer in honeybee nests

Adverse environmental conditions can be evaded, tolerated or modified in order for an organism to survive. During their development, some insect larvae spin cocoons which, in addition to protecting their occupants against predators, modify microclimatic conditions, thus facilitating thermoregulation or reducing evaporative water loss. Silk cocoons are spun by honeybee (Apis mellifera) larvae and subsequently incorporated into the cell walls of the wax combs in which they develop. The accumulation of this hygroscopic silk in the thousands of cells used for brood rearing may significantly affect nest homeostasis by buffering humidity fluctuations. This study investigates the extent to which the comb may influence homeostasis by quantifying the hygroscopic capacity of the cocoons spun by honeybee larvae. When comb containing cocoons was placed at high humidity, it absorbed 11% of its own mass in water within 4days. Newly drawn comb composed of hydrophobic wax and devoid of cocoons absorbed only 3% of its own mass. Therefore, the accumulation of cocoons in the comb may increase brood survivorship by maintaining a high and stable humidity in the cell

Do sunbirds use taste to decide how much to drink?

Nectarivorous birds typically consume smaller meals of more concentrated than of less concentrated sugar solutions. It is not clear, however, whether they use taste to decide how much to consume or whether they base this decision on post-ingestive feedback. Taste, a cue to nectar concentration, is available to nectarivores during ingestion whereas post-ingestive information about resource quality becomes available only after a meal. When conditions are variable, we would expect nectarivorous birds to base their decisions on how much to consume on taste, as post-ingestive feedback from previous meals would not be a reliable cue to current resource quality. Here, we tested whether white-bellied sunbirds (Cinnyris talatala), foraging from an array of artificial flowers, use taste to decide how much to consume per meal when nectar concentration is highly variable: they did not. Instead, how much they chose to consume per meal appeared to depend on the energy intake at the previous meal, that is how hungry they were. Our birds did, however, appear to use taste to decide how much to consume per flower visited within a meal. Unexpectedly, some individuals preferred to consume more from flowers with lower concentration rewards and some preferred to do the opposite. We draw attention to the fact that many studies perhaps misleadingly claim that birds use sweet taste to inform their foraging decisions, as they analyse mean data for multiple meals over which post-ingestive feedback will have become available rather than data for individual meals when only sensory information is available. We discuss how conflicting foraging rules could explain why sunbirds do not use sweet taste to inform their meal size decisions.National Research Foundation of South Africa, the University of Pretoria and the Scottish Universities Life Sciences Alliance.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-26562017-03-31hb2016Zoology and Entomolog

Bird pollinators differ in their tolerance of a nectar alkaloid

Although the function of nectar is to attract and reward pollinators, secondary metabolites produced by plants as anti-herbivore defences are frequently present in floral nectars. Greater understanding is needed of the effects of secondary metabolites in nectar on the foraging behaviour and performance of pollinators, and on plant–pollinator interactions. We investigated how nectar-feeding birds, both specialist (white-bellied sunbirds Cinnyris talatala) and generalist (dark-capped bulbuls Pycnonotus tricolor and Cape white-eyes Zosterops virens), respond to artificial nectar containing the alkaloid nicotine, present in nectar of Nicotiana species. Preference tests were carried out with a range of nicotine concentrations (0.1–300 μM) in two sucrose concentrations (0.25 and 1 M), and for bulbuls also in two sugars (sucrose and hexose). In addition, we measured short-term feeding patterns in white-bellied sunbirds that were offered nicotine (0–50 μM) in 0.63 M sucrose. Both nicotine and sugar concentrations influenced the response of bird pollinators to nicotine. The birds showed dose-dependent responses to nicotine; and their tolerance of high nicotine concentrations was reduced on the dilute 0.25 M sucrose diet, on which they increased consumption to maintain energy intake. White-bellied sunbirds decreased both feeding frequency and feeding duration as the nicotine concentration in artificial nectar increased. Of the three species, bulbuls showed the highest tolerance for nicotine, and sugar type (sucrose or hexose) had no effect. The indifference of bulbuls to nicotine may be related to their primarily frugivorous diet. However, the response of white-eyes to nicotine in the dilute sucrose solution was very similar to that of sunbirds, even though white-eyes are generalist nectar-feeders. Additional testing of other avian nectarivores and different secondary metabolites is required to further elucidate whether generalist bird pollinators, which utilise dilute nectars in which secondary metabolites have stronger deterrent effects, are more tolerant of ‘toxic’ nectar.The University of Pretoria and the South African National Research Foundation (NRF).http://www.wiley.com/10.1111/(ISSN)1600-048Xhb2013ab201

Effects of nicotine on the digestive performance of nectar-feeding birds reflect their relative tolerance to this alkaloid

The paradox of secondary metabolites, toxic defence compounds produced by plants, in nectar and fruits is well known. Deterrence of feeding by nectarivorous and frugivorous birds is better understood than the effect of these chemicals on the digestive performance of birds. Digestive parameters such as transit time and sugar assimilation are important in assessing nutrient utilization and deterrence may be related to post-ingestive effects involving these parameters. Nectar andmany fruits contain mainly sugars andwater, and avian consumers compensate for lowsugar content in their diet by increasing food intake: thismay also increase their intake of secondary metabolites. We investigated howthe alkaloid nicotine, naturally present in nectar of Nicotiana species, influences compensatory feeding and digestive performance of nectar-feeding birds. High nicotine concentration negatively affected compensatory feeding and apparent assimilation efficiency of white-bellied sunbirds Cinnyris talatala and Cape white-eyes Zosterops virens; but nicotine slowed gut transit time only in the latter species. In contrast, food intake and digestive performance of dark-capped bulbuls Pycnonotus tricolor was unaffected by nicotine up to a concentration of 50 μM. Bulbuls are primarily frugivorous; hence, they are more exposed to secondary metabolites than sunbirds and possibly white-eyes. Because their diet is richer in toxins, frugivorous birds may have evolved more efficient detoxification strategies than those of specialist nectar-feeding birds.South African National Research Foundation (73671) and the University of Pretoria.http://www.elsevier.com/locate/cbpa2016-12-31hb201

Plant–pollinator interactions and threats to pollination : perspectives from the flower to the landscape

Animal pollinators have driven the diversification of plants on the earth for more than 100 million years. The mutualism between plants and their pollinators rests on an exchange: food for pollinators and efficient vectoring of sexual reproduction for plants. This relationship has been shaped by many factors during the course of evolution. Competition between pollinators for access to nectar and pollen, and among flowering plants for the attention of pollinators, has influenced the shape, colour, and scent of flowers and the extent to which plants invest in the production of pollen and nectar. While many pollinators are ‘generalists’ and visit a variety of flowering plants to obtain food, close relationships between specific pollinators and plant species have developed throughout the course of evolutionary history. An important issue today, given the widespread concern about wild and managed pollinators, is determining how human activities impact the varied relationships between plants and their insect pollinators.The Royal Society and the National Research Foundation of South Africa generously funded the workshop under the SA-UK Scientific Seminars Initiative.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-24352018-01-31hb2017Zoology and Entomolog

Regulation of nutrient intake in nectar-feeding birds : insights from the geometric framework

A nectar diet is simple in nutritional composition and easily digested, but may vary greatly in its proportions of sugar and water. Here, we apply the geometric framework, a modelling approach for investigating how animals balance nutrient needs in multidimensional and dynamic nutritional environments, to captive whitebellied sunbirds (Cinnyris talatala). We address the question of how these small birds (»8 g) prioritise sugar and water intake, and how dietary salt content interacts with sugar and water intake. Sunbirds kept at 20°C and provided with moderate to high sucrose concentrations (¸1 M), together with supplementary water, converge on an intake target of 2.79 g day¡1 of sucrose and 7.72 g day¡1 of water: equivalent to 0.85 M sucrose. When the birds are given more dilute sucrose concentrations, they defend their sugar intake by over-ingesting water, up to a ceiling of 47 g day¡1. Sugar intake thus gets priority over water intake, but the birds have a Wnite capacity to overingest water to gain the target level of sugar. Regulation appears to be less precise when birds are given a choice between two sucrose solutions than when they choose between a sugar solution and supplementary water. Intake targets vary in response to internal and external factors, and sunbirds increase their sugar intake in response to increased activity and cold, irrespective of nectar concentration. They also compensate for interruptions in foraging activity, whether overnight or during the day. Interactive eVects become evident when sodium is included as a third nutrient: on very dilute nectar (·0.1 M), where sunbirds lose body mass, the addition of sodium to the diet helps to achieve the carbohydrate intake target, while raising the ceiling on water intake. This analysis provides a new perspective on nectarivory, while adding to the comparative database on nutrient regulation and emphasising water as a nutrient.The University of Pretoria, the South African National Research Foundation and the Claude Leon Foundation. DR received support from the Massey University Research Fund.http://www.springer.com/life+sci/biochemistry/journal/360ab201

Book Reviews

Book Review 1Book Title: Atlas of Microscopic Structures of Fur Skins Vol. 1Book Authors: Anton Blažej et al.Elsevier Amsterdam and SNTl, Prague, 1989. 378 pages.Book Review 2Book Title: Ornithology for AfricaBook Author: Gordon L. MacleanUniversity of Natal Press, 1990. 270 pages.Book Review 3Book Title: Biology of the Vespine WaspsBook Authors: Makoto Matsuura & Seiki YamaneSpringer-Verlag, Berlin, 1990. 323 pages, numerous figures, tables and photographs. ISBN 3-540-51900-9Book Review 4Book Title: Horns, Pronghorns, and AntlersBook Authors: Edited by G.A. Bubenik & A.B. BubenikSpringer-Verlag, New York. ISBN 0-387-97176-9. 562 pp.Book Review 5Book Title: Ecophysiology of Desert Arthropods and ReptilesBook Author: J.L. Cloudsley-ThompsonSpringer-Verlag, 1991. 203 pagesBook Review 6Book Title: Practical Taxonomic ComputingBook Author: Richard J. PankhurstCambridge University Press. 202 page

Sunbirds increase foraging success by using color as a cue for nectar quality

Nectar concentration and composition varies widely between plant species. Nectarivorous birds that associate floral characteristics with nectar quality may be able to avoid less rewarding flowers and therefore forage more efficiently. We assessed the abilities of amethyst sunbirds (Chalcomitra amethystina) to utilize color cues to discriminate between concentrated (1 M) and dilute (0.25 M) sucrose solutions. In an outdoor aviary, birds were presented with three rich feeders among six poor feeders on a feeding board. Following the assessment of baseline performance with optically identical feeders, color cues were added to the feeders for a 6 h training period. To assess the retention of learnt visual cues, birds were tested 1 and 7 days following the training. Observations lasted for 3 h, with feeders being re-arranged every 30 min to minimize spatial learning. In the absence of color cues, birds selected feeders randomly, but when color cues were available visited more rich than poor feeders. This more rapid identification of rich feeders resulted in a decrease in feeding duration and feeding frequency, compared to the baseline performance. Energy uptake from rich feeders, and therefore the rate of energy gain, increased when birds foraged with color cues. No differences were found between days 1 and 7 after training. Total energy intake decreased with visual cues, which may indicate a reduction in foraging costs when cues allow for location of rewarding feeders. Our findings demonstrate that sunbirds forage more efficiently with cues, which may lead to increased fitness.South African National Research Foundation (grant number 73671) and the University of Pretoria.http://beheco.oxfordjournals.orghb2014ab2014Zoology and Entomolog