African Sunbirds Research Articles

Punctuated evolution in the learned songs of African sunbirds.

Learned traits are thought to be subject to different evolutionary dynamics than other phenotypes, but their evolutionary tempo and mode has received little attention. Learned bird song has been thought to be subject to rapid and constant evolution. However, we know little about the evolutionary modes of learned song divergence over long timescales. Here, we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis of the order of hundreds of thousands of years or more, broken up by evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes over evolutionary timescales. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over long time periods.

Behavioural correlates of drinking speed in two West African sunbird species

ABSTRACT The effect of perching versus hovering on the drinking speed of the Cameroon Sunbird Cyanomitra oritis and the Northern Double-collared Sunbird Cinnyris reichenowi was investigated in a cage experiment. Our results support the hypothesis that the shorter handling times on flowers during hovering compared to perching are largely caused by an increase in drinking speed.

African sunbirds predominantly pollinate plants useful to humans

Abstract Birds provide multiple ecological services that benefit humans including pollination. In Africa, sunbirds are the dominant vertebrate pollinator. Here we present a species-level assessment for African sunbirds of the number and relative frequency of their food plants that have useful properties to humans. We conducted this analysis by compiling and integrating known sunbird food plants with useful tropical plant and tropical cultivated plant databases. Across Africa, 68% of the 329 genera and 44% of the 468 species of sunbirds’ known food plants are used by humans for medicine, food, building materials, or other uses. Yet most genera and species of useful plants are visited by a small number of sunbird species. The median number of sunbird species that visit a useful genus and species of plant is two and one, respectively. Of the 409 genera and 308 species of useful plants that are sunbird pollinated across one or more of the six predominant habitats for sunbirds, 67% of genera and 71% of species are pollinated by sunbird species that are forest or woodland dependent. Additionally, 58% of all genera and 83% of all species of useful plants pollinated by sunbirds are non-cultivated. In Africa, non-cultivated sunbird-pollinated useful plants are almost entirely collected, used, and traded locally rather than regionally or internationally. Our results indicate that African sunbirds provide important ecological services as pollinators that benefit humans, and these services are provided largely at a local scale. Given the decline of invertebrate and vertebrate pollinators both globally and in Africa, sunbirds are important to the long-term conservation of many useful plants in Africa and hence human well-being.

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

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.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.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.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.

Coevolutionary patterns and diversification of avian malaria parasites in African sunbirds (Family Nectariniidae)

The coevolutionary relationships between avian malaria parasites and their hosts influence the host specificity, geographical distribution and pathogenicity of these parasites. However, to understand fine scale coevolutionary host-parasite relationships, robust and widespread sampling from closely related hosts is needed. We thus sought to explore the coevolutionary history of avian Plasmodium and the widespread African sunbirds, family Nectariniidae. These birds are distributed throughout Africa and occupy a variety of habitats. Considering the role that habitat plays in influencing host-specificity and the role that host-specificity plays in coevolutionary relationships, African sunbirds provide an exceptional model system to study the processes that govern the distribution and diversity of avian malaria. Here we evaluated the coevolutionary histories using a multi-gene phylogeny for Nectariniidae and avian Plasmodium found in Nectariniidae. We then assessed the host-parasite biogeography and the structuring of parasite assemblages. We recovered Plasmodium lineages concurrently in East, West, South and Island regions of Africa. However, several Plasmodium lineages were recovered exclusively within one respective region, despite being found in widely distributed hosts. In addition, we inferred the biogeographic history of these parasites and provide evidence supporting a model of biotic diversification in avian Plasmodium of African sunbirds.

Reciprocal territorial responses of parapatric African sunbirds: species-level asymmetry and intraspecific geographic variation

Territorial competition regularly occurs between ecologically similar species with substantial divergence in territorial signals. Strong responses to heterospecific signals can result either from the conservation of broad response functions or from species discrimination with competitor recognition. The African sunbird sibling species Nectarinia moreaui and Nectarinia fuelleborni share similar niches and an extremely narrow parapatric boundary. These species sing strikingly different songs, yet have only subtly different morphologies. Familiarity with sibling species is only possible in the small contact zone where their ranges abut. A series of simulated territorial intrusion experiments reveal asymmetry in response frequency to heterospecific songs: N. moreaui respond less frequently to N. fuelleborni than to conspecific songs, whereas N. fuelleborni respond with an approximately equal frequency to both N. moreaui and conspecific songs. However, there is strong geographic variation in heterospecific song response among N. fuelleborni populations, with one allopatric population exhibiting stronger responses to conspecifics than to N. moreaui. These results indicate that N. fuelleborni populations can retain broad response functions absent contact with N. moreaui, such that competitor recognition is not necessary to explain strong territorial responses to N. moreaui. Strong geographic variation within N. fuelleborni, however, implies that spatial replication of allopatric/sympatric treatments should benefit future territorial response experiments. Lastly, a multimodal experiment in the contact zone area reveals that, following initial approaches to song signals, response differences are not greater to conspecific signals. This result suggests that associative learning may result in high heterospecific aggression via competitor recognition, even in N. moreaui, where syntopy occurs.

Interference competition between sunbirds and carpenter bees for the nectar of Hypoestes aristata

Interference competition for nectar sources has been repeatedly described between hummingbirds and various insects, but rarely recorded in other nectari-vorous birds. We observed aggressive behaviour by African sunbirds (Cinnyris reichenowi and Cinnyris bouvieri) defending the nectar plant Hypoestes aristata against carpenter bees (Xylocopa caffra and Xylocopa inconstans) in the Bamenda Highlands, Cameroon. During 200 hours of observation, we recorded 38 cases of the sunbirds attacking carpenter bees; all these intrusions occurred only in the flower-richest patches of the plant. We predict that similar aggressive interactions will occur between other Old World nectarivorous birds and insects. Such interference competition between distantly related taxa could have an important impact on the evolution of pollination systems.

Interference Competition Between Sunbirds and Carpenter Bees for the Nectar ofHypoestes aristata

Interference competition for nectar sources has been repeatedly described between hummingbirds and various insects, but rarely recorded in other nectari-vorous birds. We observed aggressive behaviour by African sunbirds (Cinnyris reichenowi and Cinnyris bouvieri) defending the nectar plant Hypoestes aristata against carpenter bees (Xylocopa caffra and Xylocopa inconstans) in the Bamenda Highlands, Cameroon. During 200 hours of observation, we recorded 38 cases of the sunbirds attacking carpenter bees; all these intrusions occurred only in the flower-richest patches of the plant. We predict that similar aggressive interactions will occur between other Old World nectarivorous birds and insects. Such interference competition between distantly related taxa could have an important impact on the evolution of pollination systems.

Best Feed Forward

Ecology![Figure][1] Cyanomitra oritis feeding on Impatiens sakeriana . CREDIT: STEPAN JANECEK New World hummingbirds and Old World sunbirds are both adapted for feeding on nectar. They share specialized traits, such as an elongated bill and a small body size. Hummingbirds, however, have become famous for their ability to hover indefinitely in front of flowers, whereas sunbirds seem less able or inclined to do so. Following on a recent study that demonstrated that African sunbirds can hover when challenged to feed from an invasive, hummingbird-pollinated New World plant ( Nicotiana glauca ), Janecek et al. have examined the pollination system of the native African plant Impatiens sakeriana, which displays a suite of characteristics common to plants that attract hovering birds: red flowers, a long flower spur, high nectar production, and an absence of nearby perching structures as is usually observed in sunbird-pollinated plants. The reproductive ecology of this plant has been a conundrum. It had been hypothesized that it evolved to be pollinated by a now-extinct hovering bird; in this species' absence, it would have to be either self- or insect-pollinated. The authors used exclusion and germination experiments along with observations to demonstrate that these plants are not capable of self-pollination and are not pollinated by insects. Further, they showed that two species of African sunbirds ( Cyanomitra oritis and Cinnyris reichenowi ) will both perch and hover at I. sakeriana flowers. Nevertheless, C. reichenowi , when perching, pierces the sides of flowers to drink the nectar, resulting in lower seed production. Therefore, the authors suggest that the distinctive flower morphology of I. sakeriana has evolved in order to induce birds to hover, instead of perch, and thus to enforce a fair trade of nectar for pollination. Oikos 119 , 10.111/j.1600-0706.2010.08612.x (2010). [1]: pending:yes

Nocturnal pectoral tuft display in the malachite sunbird

Diurnal birds generally sleep during the hours of darkness. Most male southern African sunbirds have pectoral tufts, although the function of these is not always understood. We examined nocturnal tuft display in male malachite sunbirds (Nectarinia famosa) and found that they display their pectoral tufts almost continuously throughout the night, whilst asleep. We suggest the possible function of this behaviour and suggest that these tufts might be a deterrent to predators, as they look like ‘eyes’ in the dark. A review of the use and occurrence of pectoral tufts in southern African sunbird species is also discussed. We suggest the ‘anti-predator’ hypothesis be investigated further.

Nocturnal Pectoral Tuft Display in the Malachite Sunbird

Diurnal birds generally sleep during the hours of darkness. Most male southern African sunbirds have pectoral tufts, although the function of these is not always understood. We examined nocturnal tuft display in male malachite sunbirds (Nectarinia famosa) and found that they display their pectoral tufts almost continuously throughout the night, whilst asleep. We suggest the possible function of this behaviour and suggest that these tufts might be a deterrent to predators, as they look like ‘eyes’ in the dark. A review of the use and occurrence of pectoral tufts in southern African sunbird species is also discussed. We suggest the ‘anti-predator’ hypothesis be investigated further.

African sunbirds hover to pollinate an invasive hummingbird-pollinated plant

Why do hummingbirds hover while Old World nectar-feeding birds perch? A unique opportunity to explore this question is presented by the invasion into Africa of a plant adapted for pollination by hovering hummingbirds. Like other hover-pollinated plants of the New World, the flowers of the tree tobacco Nicotiana glauca lack perches and are oriented towards open space. We find that Old World nectarivores, especially the malachite sunbird, Nectarinia famosa, hover 80% of the time when taking nectar from these flowers. They hover for up to 30 s, and are able to sustain this hovering lifestyle in an area where native nectar plants are absent. Nicotiana glauca greatly increases the local abundance of sunbirds compared with uninvaded areas. In turn, flowers visited by sunbirds formed significantly more capsules and set significantly more seed than sunbird-excluded flowers, possibly facilitating the invasion. The results suggest a prominent role for plant, rather than bird traits in determining the occurrence of hover-pollination, begging the question of why plants adapted for hover pollination do not occur outside the New World.

African sunbirds hover to pollinate an invasive hummingbird‐pollinated plant

Why do hummingbirds hover while Old World nectar‐feeding birds perch? A unique opportunity to explore this question is presented by the invasion into Africa of a plant adapted for pollination by hovering hummingbirds. Like other hover‐pollinated plants of the New World, the flowers of the tree tobacco Nicotiana glauca lack perches and are oriented towards open space. We find that Old World nectarivores, especially the malachite sunbird, Nectarinia famosa, hover 80% of the time when taking nectar from these flowers. They hover for up to 30 s, and are able to sustain this hovering lifestyle in an area where native nectar plants are absent. Nicotiana glauca greatly increases the local abundance of sunbirds compared with uninvaded areas. In turn, flowers visited by sunbirds formed significantly more capsules and set significantly more seed than sunbird‐excluded flowers, possibly facilitating the invasion. The results suggest a prominent role for plant, rather than bird traits in determining the occurrence of hover‐pollination, begging the question of why plants adapted for hover pollination do not occur outside the New World.

RETRACTED: Physiological variation in Amethyst Sunbirds ( Chalcomitra amethystina) over an altitudinal gradient: A seasonal comparison

Southern Africa is characterised by an unpredictable environment with daily and seasonal temperature fluctuations, thus posing challenging thermal conditions and increased energetic stress for endothermic vertebrates. Amethyst Sunbirds (Chalcomitra amethystina) are relatively large African sunbirds (15 g). They are considered non-migratory and thus have to cope with the temperature changes and physiological stresses a new season brings. This study compared altitudinal subpopulations and the seasonal shifts in metabolic parameters between and within the subpopulations in metabolic parameters. Amethyst Sunbirds were caught in summer and winter at three different altitudinal subpopulations; Underberg (1555 m asl), Howick (1075 m asl) and Oribi Gorge (541 m asl). Upon capture, metabolic rates of the sunbirds were measured indirectly by quantifying oxygen consumption ((.)VO2) using flow through respirometry, at 5 and 25 degrees C. Birds then underwent a 6-week acclimation period at 25 degrees C on a 12 L: 12D cycle. (.)VO2 was measured post-acclimation at 8 different temperatures (15, 5, 10, 20, 30, 28, 25 and 33 degrees C), which were ordered randomly in the experimental protocol to avoid acclimation bias. Experiments were repeated for a winter and summer season. In general, Amethyst Sunbird subpopulations from Underberg and Howick showed higher post-acclimation resting metabolic rates per temperature in winter than in summer trials. Underberg and Howick subpopulations respectively showed a significant difference between summer and winter (.)VO2 at 5 and 10 degrees C. Thermal neutral zones of all of the subpopulations of sunbirds shifted between winter and summer. Post-acclimation basal metabolic rate of sunbirds decreased significantly by 38.8% from winter to summer for the Underberg subpopulation, increased by 44.8% for the Howick subpopulation and did not change significantly for the Oribi Gorge subpopulation (5.8% decrease).

Physiological correlates of habitat association in East African sunbirds (Nectariniidae)

AbstractEast African sunbirds (Nectariniidae) vary in the degree to which they use open habitats and forest habitats. Species that use open habitats may experience more extreme temperatures and greater exposure to solar radiation than those in forest habitats. Basal rates of metabolism, body temperature and thermal conductance were compared for open habitat‐ and forest‐associated sunbirds from Kibale National Park, Uganda. Variation in basal rate of metabolism was associated with body mass, but there was no difference between forest and open habitat species. Variation in body temperature was not associated with body mass or habitat. Variation in thermal conductance was associated with body mass and habitat; open habitat species were characterized by significantly lower thermal conductances than forest species. Because reduced thermal conductance may decrease energy expenditure at low ambient temperatures and reduce exogenous heat gain at high ambient temperatures, this difference may optimize energy expenditure when temperatures are highly variable. This suggests a mechanism by which physiological characteristics may influence energetic consequences of habitat selection.

Sunbird surprise for syndromes

Predictions can be made about how a given plant might be pollinated by looking at its morphology, colour, nectar and odour. But scientists are increasingly finding that these predictions aren't reliable. The latest example is that ofMicroloma sagittatum, a member of the milkweed family, which, against all expectations, has been found to be pollinated by the South African sunbird Nectarinia chalybea.

Metabolic rate and body temperature of an African sunbird,Nectarinia Chalybea: daily rhythm and the effect of ambient temperature

The oxygen consumption (VO2) of the lesser double-collared sunbird, Nectarinia chalybea. was measured at ambient temperatures (Ta) from 7 to 35°C. The diel variation in body temperature (Tb) and wet thermal conductance (C) was also determined. The sunbirds (mean mass 8,36 g ± S.E. 0.21 g) showed a pronounced diel cycle of VO2, with a mean reduction of 50% at night. Basal metabolic rate was estimated to be 3.23 ml O2/g.h, which is 88% of the predicted value for a passerine bird of this size. There was a mean reduction in Tb of 3.6°C at night. Both day and night values of Tb decreased with decreasing Ta, as did individual values of C. Winter breeding in the south-west Cape is energetically stressful for lesser double-collared sunbirds, but they have the physiological capacity to reduce their energy expenditure substantially at night.

Daily energy costs and body weight in nectarivorous birds

1. 1. Nectar-feeding birds (New World hummingbirds, African sunbirds, Hawaiian honey-creepers) defending feeding territories have 24 hr energy costs (Kcal/day) described by the regression equation E = 4.56 W 421 2. 2. Their daily energy expenditures conform to size-related constraints, which must be regulated by appropriate balances between behavioral and physiological capacities for energy conservation.

Foraging Strategies and Energetics of East African Sunbirds at Mistletoe Flowers

Sunbirds (Nectariniidae) feeding on nectar of the mistletoe, Phragmanthera dshallensis, in central Kenya encounter two types of flowers. Closed flowers, which have not been visited previously and must be opened by the feeding bird, contain more nectar and require more feeding time than open flowers. Open flowers result from the visitation and explosive opening of closed flowers. Closed flowers are rarer overall than open flowers, although occasionally a local area may have a majority of closed flowers. The different-sized sunbird species tend to take different proportions of open and closed flowers; generally there is a positive relation between bird size and percentage of closed flowers taken. We examined benefits and costs for each bird species feeding in local patches of mistletoe. The benefits were the same for each species. The time costs varied inversely with bird size. These differences were reduced by the lower energetic costs of the smaller species. For all species the caloric benefit to cost ratio (= foraging efficiency) increased with increasing proportions of closed flowers visited. However the foraging efficiency difference between 0% and 100% closed flowers was greatest for kilimensis, indicating that kilimensis gained more by preferentially moving to patches with high proportions of closed flowers. The data on percentage closed flowers actually taken indicate that those species which should derive greater energy benefits by taking higher proportions of closed flowers tend to do so. Complete specialization on closed flowers, however, apparently is prevented by increasing search costs within and between patches. The sunbird foraging behavior is consistent with predictions based on maximizing foraging efficiencies as a function of relative energy value of the two flower types.

Temperature Regulation of the Pyrrhuloxia and the Arizona Cardinal

Temperature Regulation of the Pyrrhuloxia and the Arizona Cardinal