Long-billed Hummingbirds Research Articles

Long-and short-billed hummingbirds as pollinators of Palicourea demissa, a distylous treelet of Neotropical cloud forests.

Distyly has been interpreted as a mechanism that promotes cross-pollination between floral morphs. According to this hypothesis, pollen from anthers positioned at different heights could adhere to different body parts of the pollinator that would correspond to those points where stigmas of compatible morph contact the animal. In this regard, hummingbird species with different bill sizes may play different roles as pollinators of each morph. If pollinators mobilize more legitimate pollen towards one of the two morphs, gender specialization may occur. This work aimed to assess experimentally the role of long- and short-billed hummingbirds as pollinators of short-style (SS) and long-style (LS) flowers of Palicourea demissa, a distylous, hummingbird-pollinated treelet in Venezuelan cloud forests. Flowers were emasculated and exposed to a single visit of the hummingbird Coeligena torquata (long-billed), Heliangelus spencei (short-billed) or Adelomyia melanogenys (short-billed). Later, stigmas were removed, and pollen load counted under a microscope to calculate the probability of legitimate- and illegitimate-pollen transfer by hummingbirds. The probability analyses of pollen transference showed that short-billed hummingbirds have higher pollination probabilities from SS-anthers to LS- and SS-stigmas, and from LS-anther to LS-stigmas than from LS-anther to SS-stigmas. In contrast, long-billed hummingbirds have higher probabilities of pollen transference from LS-anthers to SS-stigmas than in other directions. A deeper view of the sexual expression of each morph in P. demissa will depend on future studies that determine possible morpho-differences in the biological function of male and female floral structures, and the role played by less frequent floral visitors as mediators of legitimate pollination between floral morphs.

Nectar volume is positively correlated with flower size in hummingbird-visited flowers in the Brazilian Atlantic Forest

Abstract:We studied the relationship between flower size and nectar properties of hummingbird-visited flowers in the Brazilian Atlantic Forest. We analysed the nectar volume and concentration as a function of corolla length and the average bill size of visitors for 150 plant species, using the phylogenetic generalized least squares (PGLS) to control for phylogenetic signals in the data. We found that nectar volume is positively correlated with corolla length due to phylogenetic allometry. We also demonstrated that larger flowers provide better rewards for long-billed hummingbirds. Regardless of the causal mechanisms, our results support the hypothesis that morphological floral traits that drive partitioning among hummingbirds correspond to the quantity of resources produced by the flowers in the Atlantic Forest. We demonstrate that the relationship between nectar properties and flower size is affected by phylogenetic constraints and thus future studies assessing the interaction between floral traits need to control for phylogenetic signals in the data.

Active pollinator choice by Heliconia 'fits the bill'.

A new study documents that a tropical plant only reproduces when pollen has been deposited by a visitor capable of extracting nectar from its deep flowers. Large, long-billed hummingbirds generally carry greater quantities of, and more genetically diverse, pollen. Thus, plants can exert more active partner choice than previously considered possible.

Quantity versus quality: identifying the most effective pollinators of the hummingbird-pollinated Vriesea rodigasiana (Bromeliaceae)

Although hummingbirds are considered the major bromeliad pollinators, different species may contribute differently to pollination. This study analyses the importance of different hummingbirds to pollination of Vriesea rodigasiana (Bromeliaceae), based on visitation frequency (a quantity component) and germinated pollen load per visit (a quality component) in the Atlantic rainforest of southeastern Brazil. This bromeliad flowers for 3–4 months with a peak in March. Its yellow, tubular flowers last about 13 h and demonstrate approach herkogamy. During flowering peak, Thalurania glaucopis visited more flowers than Ramphodon naevius, whereas by the end of the flowering season the latter visited more. Differences in hummingbird bill length resulted in different pollen placement and stigma contact. The short-billed T. glaucopis received pollen on the top of its head, depositing it on the center of the stigma, while the long-billed R. naevius received it on the proximal part of its bill, depositing it on the lower lobe of the stigma. Flowers visited by T. glaucopis had six times more pollen tubes than those visited by R. naevius. Our results suggest that this functional group of hummingbirds may be split into even smaller groups, namely short-billed and long-billed hummingbirds, based on different sites of pollen placement. Although both species were pollen vectors of V. rodigasiana, the short-billed T. glaucopis was its most effective pollinator in the area supporting Stebbin’s principle, linking floral features and good pollinators.

Plant–hummingbird interactions in the West Indies: floral specialisation gradients associated with environment and hummingbird size

Floral phenotype and pollination system of a plant may be influenced by the abiotic environment and the local pollinator assemblage. This was investigated in seven plant-hummingbird assemblages on the West Indian islands of Grenada, Dominica and Puerto Rico. We report all hummingbird and insect pollinators of 49 hummingbird-pollinated plant species, as well as six quantitative and semi-quantitative floral characters that determine visitor restriction, attraction and reward. Using nonmetric multidimensional scaling analysis, we show that hummingbird-pollinated plants in the West Indies separate in floral phenotypic space into two gradients-one associated with the abiotic environment and another with hummingbird size. Plants pollinated by large, long-billed hummingbirds had flowers with long corolla tube, large amounts of nectar and showy orange-red colouration. These attracted few or no insect species, whereas plants pollinated by small, short-billed hummingbirds were frequently pollinated by insects, particularly lepidopterans. The separation of plants related to environmental factors showed that species in the wet and cold highlands produced large amounts of dilute nectar, possessed no or a weak odour, and were associated with few insects, particularly few hymenopterans, compared to plants in the dry and warm lowlands. The most specialised hummingbird-pollinated plants are found in the West Indian highlands where they are pollinated by mainly large, long-billed hummingbirds. At the other extreme, highly generalised plants growing in the dry and warm lowlands are pollinated by small, short-billed hummingbirds and numerous insect species. This illustrates that, even within the hummingbird-pollinated flora, pollination syndrome and the degree of specialisation may vary tremendously depending on pollinator morphology and environment.

Relative pollination effectiveness of floral visitors of Pitcairnia angustifolia (Bromeliaceae)

The effectiveness of flower visitors as pollinators will determine their potential role as selective agents on flower traits. Pitcairnia angustifolia has floral characters that would fit pollination by long-billed hummingbirds, and they should be the most effective pollinators for this plant. To test this prediction, we characterized the behavior of visitors toward flowers and their pollination effectiveness. Coereba flaveola (bananaquits) was the most frequent flower visitor and acted as a primary nectar robber; however, they pollinated incidentally and deposited pollen on stigmas. The endemic short-billed hummingbird Chlorostilbon maugaeus behaved as a secondary robber and did not pollinate flowers. As expected, the long-billed hummingbird, Anthracothorax viridis, was the most efficient visitor in terms of pollen deposition; however, it was the least frequent flower visitor. Introduced Apis mellifera (honeybees) were second in efficiency at depositing pollen and performed one third of the flower visits. Estimates of the expected rate of pollen deposition by each pollinator did not identify a single most effective pollinator. For P. angustifolia at least three flower visitors including an exotic bee and a nectar robber may be equally important to reproductive success. While these results limit our ability to make predictions on the role of hummingbird-pollination on current flower evolution, they do suggest the potential for pollination redundancy among flower visitors for P. angustifolia populations.

Comportamento alimentar de beija-flores e Passeriformes nas flores de Erytrhina speciosa Andrews (Fabaceae) em uma área urbana de Londrina, Paraná, Brasil

Nine species of birds – seven hummingbirds (Trochilidae) and two Passeriformes – were observed visiting the flowers of Erythrina speciosa Andrews (Fabaceae), a hummingbird-pollinated species present on the campus of Londrina State University, Parana State, Brazil. Nectar in bagged flowers bore little relationship with nectar in flowers opened to foragers either regarding quantity or diurnal pattern of availability. Birds were more frequent early in the morning and their activity on flowers further declined, apparently following the pattern of nectar availability. The manner to which birds probed the flowers and, in consequence, their role on pollination were greatly determined by morphological traits and approaching behavior of birds. E. speciosa seemed best suited for pollination by long-billed hummingbirds but some short to medium-billed species may play some role on its pollination.

Feeding behavior of hummingbirds and perching birds on Erythrina speciosa Andrews (Fabaceae) flowers in an urban area, Londrina, Paraná, Brazil

Nine species of birds - seven hummingbirds (Trochilidae) and two Passeriformes - were observed visiting the flowers of Erythrina speciosa Andrews (Fabaceae), a hummingbird-pollinated species present on the campus of Londrina State University, Paraná State, Brazil. Nectar in bagged flowers bore little relationship with nectar in flowers opened to foragers either regarding quantity or diurnal pattern of availability. Birds were more frequent early in the morning and their activity on flowers further declined, apparently following the pattern of nectar availability. The manner to which birds probed the flowers and, in consequence, their role on pollination were greatly determined by morphological traits and approaching behavior of birds. E. speciosa seemed best suited for pollination by long-billed hummingbirds but some short to medium-billed species may play some role on its pollination.

Disturbance and Predictability of Flowering Patterns in Bird-Pollinated Cloud Forest Plants.

The distribution and flowering patterns of hummingbird-pollinated plants were compared from July 1981 to June 1983 in three patch types in cloud forest at Monteverde, Costa Rica. Study plots were: (1) four recent, large (1100-2500 m2 ) disturbances ("cutovers") produced by cutting vegetation, (2) six recent, smaller (200-600 m2 ) disturbances caused by treefalls, and (3) four plots (1600-1800 m2 ) of canopied forest. Based on published literature dealing with communities that characterize different regimes of disturbance, we tested one assumption and two hypotheses. Assumption: Plant species composition differs among the three patch types. Hypothesis 1: Phenotypic specialization by plants for co-evolved interactions with hummingbirds will be lowest in large gaps, highest in forest, and intermediate in treefalls. Hypothesis 2: Predictability of flowering phenologies and nectar production will be lowest in large gaps, highest in forest, intermediate in treefalls. Neither the assumption nor the hypotheses were supported by the results. The patch mosaic in this cloud forest was not associated with major differences in species composition of bird-pollinated plants. Most species studied were self-compatible. Most abundant in cutovers were species with long corollas, relatively specialized for attracting long-billed hummingbirds. Species with short corollas, which can be visited by many hummingbird species and some insects, were most abundant in treefalls and forest. Variation in phenological patterns showed no consistent trends among patch types. Predictability of flower and nectar production tended to be greatest in treefalls, which are foci of concentrated flowering activity by all species. Discrepancies between our results and previous studies can be ascribed to two facts. (1) Much of the literature dealing with ecological consequences of disturbance has dealt with large-scale anthropogenic disturbances such as old fields of the eastern USA, whereas we studied small, natural, or quasi-natural disturbances. (2) Studies of forest disturbance have focused on the tree layer, whereas we studied the understory herbs, shrubs, and epiphytes. Natural disturbance usually involves death and replacement of one or more trees, whereas individuals of other life forms may persist through the disturbance.

Floral Neighborhood and Pollination Success in Four Hummingbird‐Pollinated Cloud Forest Plant Species

In a cloud forest at Monteverde, Costa Rica, was examined pollen loads received by self—compatible flowers of two pairs of plant species pollinated by hummingbirds: Hansteinia blepharorachis and Razisea spicata (Acanthaceae), and Besleria triflora and Drymonia rubra (Gesneriaceae). Each pair consisted of one species (Hansteinia or Besleria) pollinated by short—billed hummingbirds and a related species (Razisea or Drymonia) pollinated by long—billed hummingbirds. At three different times per species, separated by 1—3 mo, we examined flowers on 28—40 focal plants from a wide variety of floral neighborhoods, ranging from plants isolated from conspecifics, either by distance or by other flowering species pollinated by the same hummingbirds, to plants surrounded by conspecifics. Because short—billed hummingbirds often restrict foraging to areas of high flower density, and because short—tubed flowers adapted for hummingbirds often have similar pollen placement, we predicted that short—tubed flowers isolated from conspecifics would receive fewer conspecific grains and more heterospecific grains than short—tubed flowers surrounded by conspecifics. Because long—billed hummingbirds often forage over large areas and because long—tubed flowers adapted for hummingbirds tend to diverge in pollen placement, we predicted that pollination of long—tubed flowers would be relatively unaffected by floral neighborhood. Effects on pollen loads of floral neighborhood (nearness to or isolation from other flowers) followed few patterns consistent with our prediction or with conventional theory. (1) There were no consistent effects of floral neighborhoods on numbers of heterospecific grains deposited on stigmas; in all four species, regardless of corolla length, effects of particular neighborhood variables (as determined with stepwise multiple regression) were as likely to run exactly counter to conventional models as to corroborate models. (2) In none of the 12 sampling runs did increases in absolute densities of neighboring heterospecific flowers adversely affect pollination. (3) However, in two runs, loads of conspecific grains increased with increases in the absolute density of neighboring conspecific flowers, and/or (in three runs) with increases in their relative density (proportion of conspecifics among neighboring flowers). These runs all involved short—flowered species rather than long—flowered species, tending confirm our initial prediction, but half the sampling runs, even of short—flowered species, failed to show any density—dependent effects from neighboring flowers pollinated by the same hummingbirds. Flowers frequently received fewer conspecific grains than they had ovules to be fertilized. Therefore the potential existed for floral neighborhoods to affect seed set and fitness of plants. Nevertheless, even though neotropical hummingbird—pollinated flowers have been cited as examples of species whose flowering peaks are displaced through competition for pollination, competitive effects from neighboring heterospecific plants were only sporadic in the species we examined, and were particularly infrequent in those species with long flowers adapted for long—billed hummingbirds.