The feeding ecology of Stephen's lory and nectar availability in its food plants

Stephen's lory, Vini stepheni , is one of four landbirds which are endemic to Henderson Island and until recently, its habits and ecology were unknown. I studied the diet and feeding ecology of Stephen's lory with particular reference to nectar variation in dominant food plants. Stephen's lory feeds on nectar, pollen and fruits from a variety of plants with lepidopteran larvae also forming a large component of the diet. The two plants which were dominant nectar sources for Stephen's lory produced flowers with very different nectar yields. Scaevola sericea flowers contained larger maximum volumes of more concentrated nectar than Timonius polygamus flowers. However, Scaevola flowers were a less predictable nectar resource, and grew at much lower densities, than Timonius flowers. Lories fed on the two flower types at different frequencies and it was hypothesized that the net rate of energy gained from feeding from a similar sized patch of the two plant species was comparable. Although nectar volumes of Timonius polygamus flowers decreased from the early mornings up until late afternoons, the lories did not show a corresponding daily pattern of foraging behaviour. Nectar yields also increased with the age of Timonius flowers. Stephen's lory has probably been the least affected of its genus by adverse changes to its habitat, and any information gained on the species may be useful when conservation measures of other Vini species are addressed.     

Effects of Forest Fragmentation on the Colima Long-nosed Bat (Musonycteris harrisoni) Foraging in Tropical Dry Forest of Jalisco, Mexico1

We determined the effect of forest fragmentation on the nectarivorous Colima long‐nosed bat (Musonycteris harrisoni) by observing foraging behavior of this species in disturbed and undisturbed forests on the flowers of Ceiba grandiflora (Bombacaceae). The study was conducted in the area of the Chamela‐Cuixmala Biosphere Reserve in Jalisco, Mexico. Musonycteris harrisoni was observed visiting flowers during six nights (88 visits), exclusively in undisturbed forest. This species feeds on the nectar and serves as a pollinator of C. grandiflora.     

The sweet life: diet sugar concentration influences paracellular glucose absorption

Small birds and bats face strong selection pressure to digest food rapidly in order to reduce digesta mass carried during flight. One mechanism is rapid absorption of a high proportion of glucose via the paracellular pathway (transfer between epithelial cells, not mediated by transporter proteins). Intestinal paracellular permeability to glucose was assessed for two nectarivorous passerines, the Australian New Holland honeyeater (Phylidonyris novaehollandiae) and African white-bellied sunbird (Cinnyris talatala) by measuring the bioavailability of radiolabelled, passively absorbed l -glucose. Bioavailability was high in both species and increased with diet sugar concentration (honeyeaters, 37 and 81% and sunbirds, 53 and 71% for 250 and 1000mmoll-1 sucrose diets, respectively). We conclude that the relative contribution of paracellular to total glucose absorption increases with greater digesta retention time in the intestine, and paracellular absorption may also be modulated by factors such as intestinal lumen osmolality and interaction with mediated glucose uptake. The dynamic state of paracellular absorption should be taken into account in future studies.     

Response of a traplining hummingbird to changes in nectar availability

Theory predicts that nectarivores respond to changes in profitabilityof patches of flowers or feeders by adjusting visitation rateto increase reward size. We conducted a set of experiments inan outdoor enclosure with seven feeders to determine how Phaethornislongirostris, a traplining hummingbird, adjusts its visitationrates in response to changes in sucrose solution delivery rates.Each experiment tested the response of P. longirostris to thefollowing changes in the timing and volume of sucrose solutiondelivery: (1) increases in sucrose solution abundance at allfeeders (mimicking seasonal increases in numbers of open flowersor nectar output); (2) large changes in sucrose solution availabilityat one feeder (mimicking increases or decreases of patch profitability);and (3) sudden unexpected decreases in sucrose solution availabilityat one feeder (mimicking loss of nectar to competitors). Wefound that P. longirostris (1) decreased visitation rates whenthe sucrose solution delivery rate was higher at all feeders,(2) increased visitation rates to individual feeders when their profitabilityincreased for whole days but did not significantly decrease visitationrates when feeder output decreased; and (3) responded to sudden foodlosses at a feeder (due to simulated competition) by increasinguse of that feeder for 1 or 2 h after the loss.     

Ecological fitting is a sufficient driver of tight interactions between sunbirds and ornithophilous plants

1. Plant–bird pollination interactions evolved independently on different continents. Specific adaptations can lead to their restriction when potential partners from distant evolutionary trajectories come into contact. Alternatively, these interactions can be enabled by convergent evolution and subsequent ecological fitting.
2. We studied the interactions between New World plants from the genus Heliconia, Asian plants of genus Etlingera and African sunbirds on a local farm in Cameroon. Heliconia spp. evolved together with hummingbirds and Etlingera spp. with spiderhunters —an oriental subgroup of the sunbird family.
3. Sunbirds fed on all studied plants and individual plant species were visited by a different sunbird spectrum. We experimentally documented a higher number of germinated pollen grains in sunbird‐visited flowers of Etlingera spp. For Heliconia spp., this experiment was not successful and pollen tubes were rarely observed, even in hand‐pollinated flowers, where enough pollen was deposited. The analyses of contacts with plant reproductive organs nevertheless confirmed that sunbirds are good pollen vectors for both Heliconia and Etlingera species.
4. Our study demonstrated a high ecological fit between actors of distinct evolutionary history and the general validity of bird‐pollination syndrome. We moreover show that trait matching and niche differentiation are important ecological processes also in semi‐artificial plant‐pollinator systems.