Fruit-eating Birds Research Articles

Fruit-eating birds in experimental plantings in southern Mexico

Abstract:Maintenance of biodiversity in tropical agrarian landscapes is challenging in the face of anthropomorphic simplification of habitats. As part of an experiment testing influences of planting treatment on tree recruitment in southern Mexico, counts of bird species were made over 10 years in twenty-four 30 × 30-m fenced plots in over-grazed pasture. Plots were planted with native tree species or left as unplanted controls in 2006. Annual censuses of birds in the plots from 2007–2016 indicated statistically significant increases in the number of fruit-eating species and individuals as vegetation matured, but increases in non-frugivorous species and individuals over the decade were not significant. Among four species of planted animal-dispersed trees that bore fruit during this time,Cecropia obtusifoliaconsistently produced substantial crops after 2009. In 2015, all 53 planted or passively recruited female trees of mature size of this species bore fruit. The summed body masses of fruit-eating birds in each of 24 plots were significantly correlated with rank order of available fruit per plot. Differential use of habitat patches in an agrarian landscape suggested substantial value to frugivores, but less to non-frugivorous birds than expected.

Conspecific Pollen Loads on Insects Visiting Female Flowers on ParasiticPhoradendron californicum(Viscaceae)

Desert mistletoe, Phoradendron californicum (Viscaceae), is a dioecious parasitic plant that grows on woody legumes in the Mojave and Sonoran Deserts, produces minute flowers during winter, and is dispersed by birds defecating fruits. Pollination of desert mistletoe has not been examined despite the species' reliance on insects for transporting pollen from male to female plants. I investigated the pollination of P. californicum parasitizing Acacia greggii (Fabaceae) shrubs at 3 sites at different elevations in the Mojave Desert of southern Nevada during February 2015. I examined pollen from male flowers, aspirated insects landing on female flowers, and counted pollen grains in insect pollen loads. Desert mistletoe's tricolpate pollen differed from a previous description by being oblate instead of subprolate in equatorial view. Female flowers were visited by 13 species of Diptera in 10 genera and 6 families and 3 species of Hymenoptera in 3 families. Almost all (98.5%) of the pollen carried by insects was from desert mistletoe. Five species of phytophagous fruit flies in Tephritidae were frequently found on flowers, comprising 53% of the insects collected, but carried low amounts of P. californicum pollen. Two species of blow flies in Calliphoridae, both larval decomposers of animals, were also relatively abundant on flowers and carried moderate to high pollen loads. Flies in Syrphidae, 2 predators and 1 plant-decomposer, carried varying amounts of conspecific pollen. Conspecific pollen loads also varied on a species of native bee in Halictidae and on naturalized honey bees in Apidae. Desert mistletoe appears to be pollinated mostly by tephritids, due to their abundance on female flowers, and by calliphorids. Blow flies would be more likely than fruit flies to carry pollen between male and female plants on different host shrubs due to their larger size and stronger flight. Parasitic, dioecious P. californicum plants appear to rely on a web of mutualism between fruit-eating birds and flower-fertilizing insects.

Roles of birds and bats in early tropical-forest restoration.

Restoration of tropical forest depended in large part on seed dispersal by fruit-eating animals that transported seeds into planted forest patches. We tested effectiveness of dispersal agents as revealed by established recruits of tree and shrub species that bore seeds dispersed by birds, bats, or both. We documented restoration of dispersal processes over the first 76 months of experimental restoration in southern Mexico. Mixed-model repeated-measures randomized-block ANOVAs of seedlings recruited into experimental controls and mixed-species plantings from late-secondary and mature forest indicated that bats and birds played different roles in the first years of a restoration process. Bats dispersed pioneer tree and shrub species to slowly regenerating grassy areas, while birds mediated recruitment of later-successional species into planted stands of trees and to a lesser extent into controls. Of species of pioneer trees and shrubs established in plots, seven were primarily dispersed by birds, three by bats and four by both birds and bats. Of later-successional species recruited past the seedling stage, 13 were of species primarily dispersed by birds, and six were of species dispersed by both birds and bats. No later-successional species primarily dispersed by bats established in control or planted plots. Establishment of recruited seedlings was ten-fold higher under cover of planted trees than in grassy controls. Even pre-reproductive trees drew fruit-eating birds and the seeds that they carried from nearby forest, and provided conditions for establishment of shade-tolerant tree species. Overall, after 76 months of cattle exclusion, 94% of the recruited shrubs and trees in experimental plots were of species that we did not plant.

Overlap and resource sharing in coteries of fruit-eating birds

Abstract:A range of species eating the same fruit suggests that niche overlap can occur, along with potential competition among them. To test if the overlap in the coterie of fruit-eating birds is larger than would be expected by chance, we performed a comparison with coteries generated from the use of null models. The study was carried out in an area of savanna woodland of 127 ha in Uberlândia city, Brazil. Four individuals of five zoochorous plant species were selected and 60 h of focal observation was performed on each species. We recorded species of birds that consumed fruits and the quantity of fruit removed. We used an index of Proportional Similarity (PS) between each pair of plant species, using the relative proportion of fruit taken by each bird species of each plant. The mean value of observed PS was compared with the mean PS generated from randomizations. Thirty-six bird species were recorded eating fruits in the selected plant species. The mean overlap observed (PS = 0.183) was significantly higher (P = 0.032) than the mean overlap generated by the null models (PS = 0.123). This pattern suggests that competition is not an important factor in the formation of the coteries and there is sharing of resources. The abundance of fruits offered, especially in the rainy season, and the relatively low number of frugivorous species may be factors explaining the low influence of interactions and therefore the overlap between coteries.

Functional Extinction of Birds Drives Rapid Evolutionary Changes in Seed Size

Local extinctions have cascading effects on ecosystem functions, yet little is known about the potential for the rapid evolutionary change of species in human-modified scenarios. We show that the functional extinction of large-gape seed dispersers in the Brazilian Atlantic forest is associated with the consistent reduction of the seed size of a keystone palm species. Among 22 palm populations, areas deprived of large avian frugivores for several decades present smaller seeds than nondefaunated forests, with negative consequences for palm regeneration. Coalescence and phenotypic selection models indicate that seed size reduction most likely occurred within the past 100 years, associated with human-driven fragmentation. The fast-paced defaunation of large vertebrates is most likely causing unprecedented changes in the evolutionary trajectories and community composition of tropical forests.

Specialization of Mutualistic Interaction Networks Decreases toward Tropical Latitudes

Species-rich tropical communities are expected to be more specialized than their temperate counterparts. Several studies have reported increasing biotic specialization toward the tropics, whereas others have not found latitudinal trends once accounting for sampling bias or differences in plant diversity. Thus, the direction of the latitudinal specialization gradient remains contentious. With an unprecedented global data set, we investigated how biotic specialization between plants and animal pollinators or seed dispersers is associated with latitude, past and contemporary climate, and plant diversity. We show that in contrast to expectation, biotic specialization of mutualistic networks is significantly lower at tropical than at temperate latitudes. Specialization was more closely related to contemporary climate than to past climate stability, suggesting that current conditions have a stronger effect on biotic specialization than historical community stability. Biotic specialization decreased with increasing local and regional plant diversity. This suggests that high specialization of mutualistic interactions is a response of pollinators and seed dispersers to low plant diversity. This could explain why the latitudinal specialization gradient is reversed relative to the latitudinal diversity gradient. Low mutualistic network specialization in the tropics suggests higher tolerance against extinctions in tropical than in temperate communities.

Fine‐tuning the fruit‐tracking hypothesis: spatiotemporal links between fruit availability and fruit consumption by birds in Andean mountain forests

1. The fruit-tracking hypothesis predicts spatiotemporal links between changes in the abundance of fruit-eating birds and the abundance of their fleshy-fruit resources. 2. While the spatial scale of plant-frugivore interactions has been explored to understand mismatches between observed and expected fruit-frugivore patterns, methodological issues such as the consequences of measuring fruit and frugivore abundance rather than fruit availability and fruit consumption have not been evaluated. 3. Here, we explored whether predicted fruit-frugivore spatiotemporal links can be captured with higher accuracy by proximate measurements of interaction strength. We used a 6-ha grided plot in an Andean subtropical forest to study the link between (i) fruit and fruit-eating bird abundances; (ii) fruit availability and frequency of fruit consumption; and (iii) covariation between frugivore abundance and frequency of frugivory. We evaluated these links for the entire frugivore assemblage and for the four most important species using data gathered bimonthly along a 2-year period. 4. Fleshy-fruit availability and abundance varied sharply temporally and were patchily distributed in mosaics that differed in fruit quantity. Fruit availability and abundance also varied along spatial gradients extended over the whole study plot. We found a strong response of the entire frugivorous bird assemblage to fruit availability over time, and a weakly significant relationship over space at the local scale. The main frugivore species widely differed in their responses to changes in fruit abundance in such a way that response at the assemblage level cannot be seen as the sum of individual responses of each species. Our results suggest that fruit tracking in frugivorous-insectivorous birds may be largely explained by species-specific responses to changes in the availability of fruits and alternative resources. 5. In agreement with our prediction, more accurate measurements of interaction strength described fruit-frugivore relationships better than traditional measurements. Moreover, we show that covariation between frugivore abundance, frequency of fruit consumption and fruit availability must be included in the fruit-tracking hypothesis framework to demonstrate (or reject) spatiotemporal fruit tracking. We propose that estimation of nutrient and energy availability in fruits could be a new frontier to understanding the forces driving foraging decisions that lead to fruit tracking.

Ecosystems effects 25 years after Chernobyl: pollinators, fruit set and recruitment

Animals are assumed to play a key role in ecosystem functioning through their effects on seed set, seed consumption, seed dispersal, and maintenance of plant communities. However, there are no studies investigating the consequences of animal scarcity on seed set, seed consumption and seed dispersal at large geographical scales. We exploited the unprecedented scarcity of pollinating bumblebees and butterflies in the vicinity of Chernobyl, Ukraine, linked to the effects of radiation on pollinator abundance, to test for effects of pollinator abundance on the ecosystem. There were considerably fewer pollinating insects in areas with high levels of radiation. Fruit trees and bushes (apple Malus domestica, pear Pyrus communis, rowan Sorbus aucuparia, wild rose Rosa rugosa, twistingwood Viburnum lantana, and European cranberry bush Viburnum opulus) that are all pollinated by insects produced fewer fruit in highly radioactively contaminated areas, partly linked to the local reduction in abundance of pollinators. This was the case even when controlling for the fact that fruit trees were generally smaller in more contaminated areas. Fruit-eating birds like thrushes and warblers that are known seed dispersers were less numerous in areas with lower fruit abundance, even after controlling for the effects of radiation, providing a direct link between radiation, pollinator abundance, fruit abundance and abundance of frugivores. Given that the Chernobyl disaster happened 25years ago, one would predict reduced local recruitment of fruit trees if fruit set has been persistently depressed during that period; indeed, local recruitment was negatively related to the level of radiation and positively to the local level of fruit set. The patterns at the level of trees were replicated at the level of villages across the study site. This study provides the first large-scale study of the effects of a suppressed pollinator community on ecosystem functioning.

Local Demand Drives a Bushmeat Industry in a Philippine Forest Preserve

Unregulated hunting can severely affect wildlife populations, particularly in the tropics. From May to October, 2011, we documented target species, hunting techniques, and demand and sale of bushmeat from a local community located at the base of a forested National Park on an isolated mountain (over 10,000 ha) in southern Luzon, the Philippines. The prey taken by hunters (i.e., poachers) included 22 invertebrate and vertebrate species. The main prey items were fruit-eating birds, bats, civets and wild pigs, but the most sought-after prey were flying foxes. Money was the major driver of bushmeat hunting in our study area. Bushmeat was sold and consumed almost entirely by residents of the local community and nearby towns, as hunters stated that they do not have demand from regional urban markets. Localized consumption suggests that focused conservation efforts may be effective in reducing the documented hunting pressures. Fines for hunting endangered species, according to hunters, were a deterrent. Because of limited law enforcement in our study area, however, conservation efforts such as teaching local hunters to avoid endangered species or encouraging them to monitor local animal populations may be the best bottom-up approach to minimize the negative effects of hunting.

Spatiotemporal Variation of Mistletoes: a Dynamic Modeling Approach

Mistletoes are common aerial stem-parasites and their seeds are dispersed by fruit-eating birds. In the mutually beneficial relationships between mistletoes and bird species that disperse mistletoes' seeds, the preference of birds for infected trees influences the spread of mistletoes and the spatiotemporal pattern formation of mistletoes. We formulate a deterministic model to describe the dynamics of mistletoes in an isolated patch containing an arbitrary number of trees. We establish concrete criterions, expressed in terms of the model parameters, for mistletoes establishing in this area. We conduct numerical simulations based on a field study to reinforce and expand our results.

Diel variations in plasma glucose concentration in some South African avian frugivores

We examined diel variations in the plasma glucose concentrations (PG1u) of avian blood, by measuring PG1u in four South African fruit-eating birds: the Cape White-eye(Zosterops virens), Knysna Turaco (Tauraco corythaix), Red-winged Starling (Onychognathus morio) and Speckled Mousebird (Colius striatus). Species were chosen as representatives of a range of body sizes and from the passerines and non-passerines. Birds were maintained in controlled environment rooms and PG1u were measured at four times of the day, at sunrise (0600 hours), midday (1200 hours), sunset (1800 hours) and midnight (2400 hours). Interspecific variation in mass and both the interspecific and intraspecific variation in PG1u were found to be significant for all species. PG1u of Red-winged Starlings and Knysna Turacos were highest after overnight fasting, whereas peak PG1u in Speckled Mousebirds and Cape White-eyes were recorded at midday. The lowest PG1u was recorded after overnight fasting in Speckled Mousebirds whereas the lowest PG1u were recorded at midnight in the three other species. Whereas the Red-winged Starlings, Knysna Turacos and Cape White-eyes clearly increase their PG1u via the processes of gluconeogenesis, Speckled Mousebirds apparently do not. Previous studies involving the comparison of avian PG1u have not specified sampling times and this study clearly demonstrates that PG1u of birds vary over time, thereby highlighting the need for the specification of sampling times in future sampling of avian PG1u.

A univariate analysis of variance design for multiple-choice feeding-preference experiments: A hypothetical example with fruit-eating birds

I consider statistical problems in the analysis of multiple-choice food-preference experiments, and propose a univariate analysis of variance design for experiments of this type. I present an example experimental design, for a hypothetical comparison of fruit colour preferences between two frugivorous bird species. In each fictitious trial, four trays each containing a known weight of artificial fruits (red, blue, black, or green) are introduced into the cage, while four equivalent trays are left outside the cage, to control for tray weight loss due to other factors (notably desiccation). The proposed univariate approach allows data from such designs to be analysed with adequate power and no major violations of statistical assumptions. Nevertheless, there is no single “best” approach for experiments of this type: the best analysis in each case will depend on the particular aims and nature of the experiments.

Provenance, guts, and fate: Field and experimental evidence in a host-mistletoe-bird system

Theory suggests that host—parasite interaction should lead to local adaptation of parasites to their host. In mistletoe—host tree interactions the foraging patterns of fruit-eating birds can play an important role in host local adaptation, depending on the tree species on which the mistletoe fruits were consumed (host provenance) and the tree species on which the mistletoe seeds were deposited (host fate). Yet this interaction has not been previously documented. To determine the effects of host provenance, bird gut processing, and host fate on mistletoe seed germination and seedling establishment of Psittacanthus calyculatus, we conducted a seed inoculation experiment in Tlaxcala, Mexico. Mistletoe fruits were collected from Crataegus pubescens (Cp), Prunus serótina (Ps), and Salix bonplandiana (Sb) and measured. We then manually removed the exocarp and pulp of half the fruits, and the other half were given to grey silky-flycatchers (Ptilogonys cinereus) for gut processing. Obtained seeds of both groups of fruits were measured and deposited on branches of other trees of the same 3 host species in a full factorial design. Mistletoe fruit size varied significantly among host tree species, but differences did not coincide with those in gut retention time. Bird gut processing and the host provenance X host fate interaction were the best predictors for the occurrence of germination and establishment of seedlings. Seed germination and seedling establishment were more likely when seeds were gut processed by birds, but gut retention time had no significant effects. The significant host provenance X host fate interaction was largely due to higher success of mistletoe seeds from Sb to Sb and lower success from Sb to Ps. Our results suggest that to understand the efficiency of infection of P calyculatus and possibly other mistletoe species, the linked effects of the digestive processes undergone by mistletoe seeds and the species of host trees where the seeds were consumed and ultimately deposited should be considered.

Feeding visit time of fruit-eating birds in Cerrado plants: revisiting the predation risk model

Fruiting plants that attract frequent visits by fruit-eating birds tend to be predictable patches for a predator. Consequently, the risk of a predator attack increases the longer a bird stays on a fruiting plant. We tested whether large and cryptic species of fruit-eating birds spend more time per feeding visit than smaller and conspicuous ones in fruiting plants of the Brazilian Cerrado. Data were obtained from the literature for eight fruiting plant species and from field observations of birds feeding on fruits of Zanthoxylum rhoifolium (Rutaceae). We searched for a positive linear relationship between the mean visit time and the total length of the species, considering bird color as a covariate. Feeding visits of the large and cryptic bird species lasted longer than feeding visits of small and conspicuous species. Large birds may be safer from predators because large predators are less common. Cryptic birds may be difficult to be detected by predators and, consequently, may be less likely to be attacked by predators than conspicuous birds. Thus, our results provide support to the hypothesis that vulnerable bird species spend less time foraging in fruiting plants.

Do Nectar- and Fruit-Eating Birds Have Lower Nitrogen Requirements Than Omnivores? an Allometric Test

AbstractWe used an allometric approach to compare the minimum nitrogen requirements (MNR) and the total endogenous nitrogen loss (TENL) of nectar- and fruit-eating birds with those of omnivorous birds. These two parameters were 4× higher in omnivores than in nectarivores and frugivores. In nectarivorous-frugivorous birds, MNR was 152.8 mg N kg−0.76 day−1; in omnivorous birds, it was 575.4 mg N kg−0.76 day−1. Similarly, TENL was 54.1 mg N kg−0.69 day−1 in nectarivores-frugivores, and 215.3 mg N kg−0.69 day−1 in omnivores. The residuals of the allometric relationships between TENL and MNR and body mass were positively correlated, which suggests that a large proportion of the interspecific variation in MNR is explained by variation in TENL. Although our results show that nectar- and fruit-eating birds have low nitrogen requirements, the mechanisms that these animals use to conserve nitrogen remain unclear.¿Tienen las Aves Nectrarívoras y Frugívoras Requerimientos de Nitrógeno Menores que las Omnívoras? Una Prueba Alométrica

DO NECTAR- AND FRUIT-EATING BIRDS HAVE LOWER NITROGEN REQUIREMENTS THAN OMNIVORES? AN ALLOMETRIC TEST

Abstract We used an allometric approach to compare the minimum nitrogen requirements (MNR) and the total endogenous nitrogen loss (TENL) of nectar- and fruit-eating birds with those of omnivorous birds. These two parameters were 4× higher in omnivores than in nectarivores and frugivores. In nectarivorous-frugivorous birds, MNR was 152.8 mg N kg−0.76 day−1; in omnivorous birds, it was 575.4 mg N kg−0.76 day−1. Similarly, TENL was 54.1 mg N kg−0.69 day−1 in nectarivores-frugivores, and 215.3 mg N kg−0.69 day−1 in omnivores. The residuals of the allometric relationships between TENL and MNR and body mass were positively correlated, which suggests that a large proportion of the interspecific variation in MNR is explained by variation in TENL. Although our results show that nectar- and fruit-eating birds have low nitrogen requirements, the mechanisms that these animals use to conserve nitrogen remain unclear. ?Tienen las Aves Nectrarivoras y Frugivoras Requerimientos de Nitrogeno Menores que las Omnivoras? Una...

Scaring Fruit-eating Birds from Orchards

Scaring Fruit-eating Birds from Orchards

Spatial and temporal variation in fruit and fruit-eating birds in the Taita Hills, south-east Kenya

We studied the spatial and temporal variation in fruit abundance and frugivorous bird densities in a large-sized (135ha), a medium-sized (95ha) and five small-sized (each 2–8ha) forest fragments in the Taita Hills, Kenya. The large and medium patches were respectively divided into six and three plots, while the small patches were each treated as a single plot. A pilot analysis established that the plots were sufficiently independent. Three separate census-rounds were conducted in all plots. We found significant variation in fruit density amongst the three fragment-size categories, but no significant temporal variation. Five 'common frugivores' provided sufficient data for detailed analyses. Spatially, we found significant variation in their densities, but no significant temporal variation. Overall, frugivore numbers did not appear to track fruit supplies across different fragments over time. These findings suggest that the distribution and movements of birds were most likely related to, and/or limited by, other factors such as nesting needs and fragmentation effects rather than fruit. The absence of long-distance resource tracking suggests a lack of long-distance dispersal, which implies (along with obvious ramifications for gene flow) minimal chances for recolonisation following local extinctions for tree species that depend on these birds for seed dispersal.

Forest fragmentation severs mutualism between seed dispersers and an endemic African tree.

Because bird species are lost when forests are fragmented into small parcels, trees that depend on fruit-eating birds for seed dispersal may fail to recruit seedlings if dispersal agents disappear. We tested this prediction in rainforest in the East Usambara Mountains of Tanzania, by using the endemic tree Leptonychia usambarensis (Sterculiaceae) and birds that disperse its seeds. We investigated bird abundance and Leptonychia dispersal ecology in fragments isolated for >70 yr, as compared with 3,500 ha of continuous forest. Birds that dispersed Leptonychia seeds in continuous forest were rare or absent in small fragments, where fewer seeds were removed from each tree, far fewer seedlings occurred >10 m from parent trees, and far more seedlings occurred in dense aggregations under parental crowns. Overall, our samples showed that fewer juvenile Leptonychia recruited in fragments than in continuous forest. We provide solid evidence that deficient dispersal due to habitat fragmentation seriously impacts the reproductive cycle of a tropical bird-dispersed tree.

Where Does a Fruit-Eating Bird Deposit Mistletoe Seeds? Seed Deposition Patterns and an Experiment

The distribution of desert mistletoes (Phoradendron californicum) among mesquite (Prosopis velutina) hosts is significantly aggregated. We hypothesized that the aggregation of mistletoes among hosts is produced by the pattern of seed rain generated by seed dispersers. We tested whether frugivorous Phainopeplas (Phainopepla nitens) foraged preferentially, and hence deposited mistletoe seeds disproportionately, in already parasitized mesquites. We found that Phainopeplas favored parasitized tall trees as perching and feeding sites and deposited mistletoe seeds disproportionately on trees with these characteristics. To assess experimentally the effect of the presence of mistletoes on seed deposition, we removed mistletoes from host trees. Before mistletoe removal, seed deposition was equivalent and temporally correlated in pairs of control and removal trees. After removal, deposition was lower into removal trees than into unmanipulated trees. Although mistletoe removal resulted in lower seed deposition, it did not eliminate it. We inferred that seed deposition into parasitized hosts can result from deposition of seeds originating from within a host and from other infected hosts. We conclude that the response of seed-dispersing birds to mistletoes leads to disproportionate seed deposition into already parasitized trees and that the heterogeneous distribution of seeds among hosts created by birds contributes to the clumped distribution of mistletoes among hosts.