Interactions between birds and fruit in a temperate woodland

Summary The phenology of fruit trees and avian consumption of fruit were examined in Wytham wood, Oxford in 1979–1980. Ripe fruit was available to and fed upon by birds from late August until early May. Observations made on a daily transect indicated that most of the fruit was eaten by tits and thrushes, but the two families differed in the seasonal consumption and species of fruit taken. Tits took fruits of Elder, Bramble, White Bryony, Honeysuckle, Black Bryony, and Woody Nightshade at the beginning of the season only, while thrushes consumed fruits of Elder, Bramble, Hawthorn, Sloe, Rose, and Ivy mainly in the middle and end of the season. Members of these two families also visited different habitat types following the consumption of fruit, probably effecting different patterns of dispersal. There was no correlation between feeding preferences and the abundance or profitabilities (as defined by Pyke et al. 1977) of fruits with respect to total nitrogen, total proteins, total carbohydrates, total fats, or kilocalories. It is concluded that other factors such as palatability or content of other nutrients may be important in determining the feeding preferences of different species of frugivorous birds.     

Functional heterogeneity in a plant–frugivore assemblage enhances seed dispersal resilience to habitat loss

The ability of ecosystems to maintain their functions after disturbance (ecological resilience) depends on heterogeneity in the functional capabilities among species within assemblages. Functional heterogeneity may affect resilience by determining multiplicity between species in the provision of functions (redundancy) and complementarity between species in their ability to respond to disturbances (response diversity), but also by promoting the maintenance of biological information that enables ecosystems to reorganize themselves (ecological memory). Here, we assess the role of the components of the functional heterogeneity of a plant–frugivore assemblage on the resilience of seed dispersal to habitat loss. For three years, we quantified the distributions of fruits, frugivorous thrushes (Turdus spp.) and dispersed seeds, as well as frugivore diet and movement, along a gradient of forest cover in N Spain. The abundances and the spatial distributions of fruits and birds varied between years. The different thrushes showed similar diets but differed in spatial behavior and response to habitat loss, suggesting the occurrence of both functional redundancy and response diversity. Forest cover and fruit availability affected the spatial distribution of the whole frugivore assemblage. Fruit tracking was stronger in years when fruits were scarcer but more widespread across the whole fragmented landscape, entailing larger proportions of seeds dispersed to areas of low forest cover and open microhabitats. Rather than depending on redundancy and/or response diversity, seed dispersal resilience mostly emerged from the ecological memory conferred by the inter‐annual variability in fruit production and the ability of thrushes to track fruit resources across the fragmented landscape. Ecological memory also derived from the interaction of plants and frugivores as source organisms (trees in undisturbed forest), mobile links (birds able to disperse seeds into the disturbed habitat), and biological legacies (remnant trees and small forest patches offering scattered fruit resources across the landscape).     

Fleshy fruits of indigenous and adventive plants in the diet of birds in forest remnants, Nelson, New Zealand

The relationship between fleshy-fruited indigenous species and adventive weeds in the diet of 500 mist-netted birds was studied in forest remnants of differing size and degree of modification. Fruit abundance Peaked in March and April, and most fruit was either red/orange or purple/black. The physical parameters of adventive and indigenous fruits were not significantly different. Six of the 15 passerine species netted are frugivores, and of those netted 77% had eaten fruit. They were divisible into three groups: endemic (bellbirds, Anthornis melanura; tuis, Prosthemadera novaeseelandiae), non-endemic but indigenous (silvereyes, Zosterops lateralis), and adventive (blackbirds, Turdus merula; song thrushes, T. philomelos; starlings, Sturnus vulgaris). Bird diets varied between the groups and according to fruit availability as determined by sires and seasons. Endemic birds ate the least adventive fruit; bellbirds ate mainly Podocarpus hallii and Coprosma robusta fruits at all sites. Tuis had a varied diet, including some adventive fruits. Silvereyes ate the widest range of indigenous and adventive fruits. Blackbirds and, to a smaller extent, song thrushes ate many of the same indigenous fruits as the other bird groups, but their diet included more adventive fruits, e.g., Berberis glaucocarpa. Starlings were caught only when they fed on Sambucus nigra, but they also ate a few indigenous fruits. There was little seasonal variation in bird numbers caught. Adventive species extended the seasonal availability of fruits into winter, particularly in the forest remnant closest to a town, which had the highest proportion of adventive fruits. Several weed species distributed mainly by non-endemic and adventive birds are forming new secondary vegetation. Some have large fruit crops which generally offer little food for endemic birds. Where fruiting weeds pre-empt sites that may have been occupied by native species, they create an inferior habitat for endemic birds. However, the non-endemic and adventive birds also disperse indigenous fruits into early successional vegetation, and the importance of their seed rain for conservation of biodiversity will therefore depend on the site.     

Experimental fruit removal does not affect territory structure of wintering Hermit Thrushes

ABSTRACT.   Food is generally considered to be the primary resource structuring winter territories in migrant songbirds, but there is little experimental evidence to support this. In southeastern Louisiana, ripe fruits, consumed opportunistically in the absence of preferred arthropod resources, are a primary food resource for wintering Hermit Thrushes ( Catharus guttatus ). To test the possible role of food in controlling space use during the winter, we reduced fruit availability in the territories of wintering Hermit Thrushes and compared responses of these thrushes to those in control territories where fruit availability was not altered. We found that thrushes did not adjust either territory size or location in response to midwinter reduction of fruit availability. One possible explanation for this lack of response is that sufficient food, including arthropods, was available in thrush territories even after removal of fruit. Another possibility is that the removal of fruit did reduce food levels below the level needed to meet energetic needs, but social constraints on territory structure, dictated by fall settlement spacing and maintained by agonistic interactions, prevented birds from adjusting territories to match food supply later in the season.     

FLOWER,FRUIT AND SEED ABORTION IN TROPICAL FOREST TREES: IMPLICATIONS FOR THE EVOLUTION OF PATERNAL AND MATERNAL REPRODUCTIVE PATTERNS

Flower, fruit and immature seed abortion was studied in seven self-incompatible species of trees in a tropical lowland semideciduous forest. The species showed considerable variability in fruit and seed set and the rate at which flowers and fruits were aborted. The amount of flower and fruit abortion also varied over time within species. Small samples of open-pollinated flowers in three species showed adequate amounts of pollen on the stigma, but it could not be determined whether the pollen was compatible or incompatible. In a species with multiseeded fruits, the aborted fruits contained significantly fewer seeds than those retained on the plant. Position of fruit within the inflorescence and of seed within the ovary also had a marked effect on abortion: fruits and seeds at certain positions had a higher probability of abortion than those at other positions. Experiments to test the effect of pollen source on abortion were inconclusive. The factors underlying abortions were evaluated in the context of three mutually non-exclusive hypotheses. It is concluded that selection for increased pollen dispersal and uncertainty in paternity of the zygotes are major factors underlying abortions.     

The ecological role of killer yeasts in natural communities of yeasts

The killer phenomenon of yeasts was investigated in naturally occurring yeast communities. Yeast species from communities associated with the decaying stems and fruits of cactus and the slime fluxes of trees were studied for production of killer toxins and sensitivity to killer toxins produced by other yeasts. Yeasts found in decaying fruits showed the highest incidence of killing activity (30/112), while yeasts isolated from cactus necroses and tree fluxes showed lower activity (70/699 and 11/140, respectively). Cross-reaction studies indicated that few killer-sensitive interactions occur within the same habitat at a particular time and locality, but that killer-sensitive reactions occur more frequently among yeasts from different localities and habitats. The conditions that should be optimal for killer activity were found in fruits and young rots of Opuntia cladodes where the pH is low. The fruit habitat appears to favor the establishment of killer species. Killer toxin may affect the natural distribution of the killer yeast Pichia kluyveri and the sensitive yeast Cryptococcus cereanus. Their distributions indicate that the toxin produced by P. kluyveri limits the occurrence of Cr. cereanus in fruit and Opuntia pads. In general most communities have only one killer species. Sensitive strains are more widespread than killer strains and few species appear to be immune to all toxins. Genetic study of the killer yeast P. kluyveri indicates that the mode of inheritance of killer toxin production is nuclear and not cytoplasmic as is found in Saccharomyces cerevisiae and Kluyveromyces lactis.     

Some aspects of frugivory by bird populations using coastal dune scrub in Lincolnshire

The fruit diets of Sylvia warblers, and some thrushes, were studied during 1989 at a coastal scrubland site, using faecal examination. Fruit feeding commenced as the earliest berries ripened in late July, but there were differences of timing between species. Amongst both warblers and thrushes, the larger species commenced earlier and ate more fruit. Almost all Blackcap and Garden Warbler faeces examined from early August contained some fruit remains, as did most Whitethroat faeces from mid-month. Mean fruit contents of faecal samples exceeded 80% infrequently, indicating that even the most frugivorous species always took other food, normally insects, to supplement their diet. Each species differed in their fruit diet: Blackcaps, and to a lesser extent Garden Warblers, ate Woody Nightshade berries in preference to Blackberries, as they are structurally adapted for feeding on the former plant. Only inexperienced juveniles of other species regularly chose the Nightshade berries. Elder berries, abundant from late August, became the preferred fruit for all Sylvia species. Using data from an earlier investigation, 1 it is shown that by feeding on Elder berries, migrating Blackcaps can obtain 75–90% of their daily energy requirements in 10% of daylight hours.     

Taste and Physiological Responses to Glucosinolates: Seed Predator versus Seed Disperser

In contrast to most other plant tissues, fleshy fruits are meant to be eaten in order to facilitate seed dispersal. Although fleshy fruits attract consumers, they may also contain toxic secondary metabolites. However, studies that link the effect of fruit toxins with seed dispersal and predation are scarce. Glucosinolates (GLSs) are a family of bitter-tasting compounds. The fleshy fruit pulp of Ochradenus baccatus was previously found to harbor high concentrations of GLSs, whereas the myrosinase enzyme, which breaks down GLSs to produce foul tasting chemicals, was found only in the seeds. Here we show the differential behavioral and physiological responses of three rodent species to high dose (80%) Ochradenus’ fruits diets. Acomys russatus, a predator of Ochradenus’ seeds, was the least sensitive to the taste of the fruit and the only rodent to exhibit taste-related physiological adaptations to deal with the fruits’ toxins. In contrast, Acomys cahirinus, an Ochradenus seed disperser, was more sensitive to a diet containing the hydrolyzed products of the GLSs. A third rodent (Mus musculus) was deterred from Ochradenus fruits consumption by the GLSs and their hydrolyzed products. We were able to alter M. musculus avoidance of whole fruit consumption by soaking Ochradenus fruits in a water solution containing 1% adenosine monophosphate, which blocks the bitter taste receptor in mice. The observed differential responses of these three rodent species may be due to evolutionary pressures that have enhanced or reduced their sensitivity to the taste of GLSs.     

Frugivore Behavioural Details Matter for Seed Dispersal: A Multi-Species Model for Cantabrian Thrushes and Trees

Animal movement and behaviour is fundamental for ecosystem functioning. The process of seed dispersal by frugivorous animals is a showcase for this paradigm since their behaviour shapes the spatial patterns of the earliest stage of plant regeneration. However, we still lack a general understanding of how intrinsic (frugivore and plant species traits) and extrinsic (landscape features) factors interact to determine how seeds of a given species are more likely to be deposited in some places more than in others. We develop a multi-species mechanistic model of seed dispersal based on frugivore behavioural responses to landscape heterogeneity. The model was fitted to data from three-years of spatially-explicit field observations on the behaviour of six frugivorous thrushes and the fruiting patterns of three fleshy-fruited trees in a secondary forest of the Cantabrian range (N Spain). With such model we explore how seed rain patterns arise from the interaction between animal behaviour and landscape heterogeneity. We show that different species of thrushes respond differently to landscape heterogeneity even though they belong to the same genus, and that provide complementary seed dispersal functions. Simulated seed rain patterns are only realistic when at least some landscape heterogeneity (forest cover and fruit abundance) is taken into account. The common and simple approach of re-sampling movement data to quantify seed dispersal produces biases in both the distance and the habitat at which seeds arrive. Movement behaviour not only affects dispersal distance and seed rain patterns but also can affect frugivore diet composition even if there is no built-in preference for fruiting species. In summary, the fate of seeds produced by a given plant species is strongly affected by both the composition of the frugivore assemblage and the landscape-scale context of the plant location, including the presence of fruits from other plants (from the same or different species).     

Yeast succession in the Amazon fruit Parahancornia amapa as resource partitioning among Drosophila spp.

The succession of yeasts colonizing the fallen ripe amapa fruit, from Parahancornia amapa, was examined. The occupation of the substrate depended on both the competitive interactions of yeast species, such as the production of killer toxins, and the selective dispersion by the drosophilid guild of the amapa fruit. The yeast community associated with this Amazon fruit differed from those isolated from other fruits in the same forest. The physiological profile of these yeasts was mostly restricted to the assimilation of a few simple carbon sources, mainly L-sorbose, D-glycerol, DL-lactate, cellobiose, and salicin. Common fruit-associated yeasts of the genera Kloeckera and Hanseniaspora, Candida guilliermondii, and Candida krusei colonized fruits during the first three days after the fruit fell. These yeasts were dispersed and served as food for the invader Drosophila malerkotliana. The resident flies of the Drosophila willistoni group fed selectively on patches of yeasts colonizing fruits 3 to 10 days after the fruit fell. The killer toxin-producing yeasts Pichia kluyveri var. kluyveri and Candida fructus were probably involved in the exclusion of some species during the intermediate stages of fruit deterioration. An increase in pH, inhibiting toxin activity and the depletion of simple sugars, may have promoted an increase in yeast diversity in the later stages of decomposition. The yeast succession provided a patchy environment for the drosophilids sharing this ephemeral substrate.     

Preferences of cedar waxwings in the laboratory for fruit species,colour and size: A comparison with field observations

Fruit preferences of cedar waxwings, Bombycilla cedrorum, in the laboratory were compared with preferences in the field to identify fruit characteristics that influence choice by avian dispersers. Waxwings ate 12 of 13 species of fruits offered individually in laboratory tests, but in the field ate only eight of the same 13 species. When given a choice of 10 fruit species offered simultaneously, waxwings showed a strong preference for fruits that were small or red. Preferences for fruit species in the laboratory were not correlated with morphological or nutritional characteristics of the fruits. When offered food that differed only in colour, waxwings initially preferred red over blue, yellow and green. In later tests, preference for red fruit was less marked. In tests for size preference, waxwings preferred small pieces of fruit (6 mm) over medium pieces (9 mm), and medium pieces over those that were large (12 mm). Sizes of fruits preferred in the field and in the laboratory tests were approximately 6·0–7·5 mm. Thus, waxwings can discern differences in food items and they have definite preferences. The lack of complete agreement between preferences for fruits in the field and in the laboratory suggests that factors important in the field but controlled in the laboratory (e.g. abundance, location) override preferences for certain fruits. However, some fruit characteristics, particularly size, were consistently influential in the laboratory and in the field.     

A comparative study of interspecific variation in fruit size among Australian eucalypts

We examined variation in woody fruit size among 362 Australian Eucalyptus species with respect to predictions relating fruit size to fire exposure and rainfall. Predictions for fruit size variation were established that focussed on selection for small or large seeds, given a positive allometric relationship between fruit and seed size within the genus, and on the potential for fruits to protect their valuable seed contents. Comparatively smaller fruits were found in species that continually experience frequent disturbance by fire, while both small and large fruits were found among species subjected to both short and long fire intervals. In the latter case where a broad range of fire intervals is possible, some species have adopted a strategy of producing small seeds that provide superior colonisation ability in disturbed conditions, while other species have adopted a strategy of producing large seeds which are more competitive during longer intervals between disturbance by fire. Only when taxonomic membership at the subgeneric level was accounted for in analyses across all species, did a significant relationship emerge between fruit size and rainfall independently of fire interval and plant height; comparatively larger fruits were found in species experiencing lower average annual rainfall in the subgenera Eucalyptus and Symphyomyrtus. In contrast to previous studies, larger fruits were found only in short species, while small fruits were found in both short and tall species. Many short species have adopted a strategy of protecting their seeds from high fire intensity by producing larger fruit. Since tall species can elevate their fruit far above high fire intensity, they make considerable energy savings by producing smaller fruit. It remains an open question as to why small fruit size occurs in some short species, but we suggest that these species may invest more heavily in vegetative regrowth after fire than in re-establishment by seed.     

Fruit size and shape: Allometry at different taxonomic levels in bird-dispersed plants

Summary The likelihood that a plant's seeds will be dispersed by fruit-eating birds may depend upon the size and shape of its fruits. Assuming that elongate fruits can be swallowed more easily than spherical fruits of equal volume and that plant fitness is enhanced by seed dispersal by many individuals and species of birds, natural selection should favour increasing fruit elongation with increasing fruit size in bird-dispersed plants. According to this view, this allometric pattern would be adaptive. Alternatively, fruit shape in bird-dispersed plants may be constrained by development or phylogeny. To determine whether there was any evidence to support the adaptive allometry hypothesis, we examined allometric relationships between length and diameter in fruits and seeds in a group of neotropical bird-dispersed plant species. Using the major axis technique, we regressed ln(diameter) on ln(length) for fruits and seeds at various taxonomic levels: (1) within individual trees ofOcotea tenera (Lauraceae) (2) among 19 trees within a population ofO. tenera, as well as among pooled fruits from multiple trees within 20 other species in the Lauraceae, (3) among 25 sympatric species within a plant family (Lauraceae) and (4) among 167 species representing 63 angiosperm families within a plant community in Monteverde, Costa Rica. At most taxonomic levels, a tendency for fruit length to increase more rapidly than fruit diameter among fruits (negative allometry) occurred more frequently than expected by chance. Estimated slopes of the regressions of fruit length on fruit diameter were < 1 within 15 of the 19 individualO. tenera trees, among tree means withinO. tenera, among pooled fruits within 16 of the 20 other species in the Lauraceae, among species means within the Lauraceae and among means of all bird-dispersed species in the lower montane forests of Monteverde. Seed allometry showed similar patterns, although for both fruits and seeds the broad confidence intervals of the slopes estimated by major axis regression overlapped 1 in many cases. Among the 63 Monteverde family means, fruit length and diameter scaled isometrically. Based on measurements of ontogenetic changes in fruit shape in a single species,O. viridifolia, we found no evidence that negative allometry in fruit shape within the Lauraceae was an inevitable consequence of developmental constraints. Instead, increasing elongation of fruits and seeds in certain plant taxa is consistent with adaptation to gape-limited avian seed dispersers. Contrary results from vertebrate-dispersed species from Malawi and Spain may reflect differences between the New and Old World in plant taxa, seed dispersers or evolutionary history.     

Alternative seed-handling strategies in primates: seed-spitting by long-tailed macaques (Macaca fascicularis)

Summary The seeds in fruits consumed by primates may be chewed and digested, swallowed and defecated intact, or separated from the flesh and spat out. We show by a combination of close field observations and experiments with caged animals, that long-tailed macaques (Macaca fascicularis) have a remarkably low threshold of 3–4 mm for swallowing seeds and also that wild macaques rarely break them. The seeds of 69% of the ripe fruit species eaten are spat out intact or cleaned outside the mouth and dropped. Seed-spitting significantly reduces the swallowed food bulk and may lessen the risk of releasing seed toxins during mastication. However, it requires that even small fruits are processed in the mouth one or a few at a time. We suggest that fruit storage in the cheek pouches of cercopithecine monkeys allows them to spit seeds individually without excessively slowing fruit intake while feeding on patchily distributed fruit. In contrast, Apes and New World monkeys apparently swallow and defecate most ripe seeds in their diet and colobine monkeys break and digest them, detoxifying seed defenses by bacterial fermentation.     

Factors affecting seed rain beneath fleshy-fruited plants

We investigated factors affecting seed rain beneath nine fleshy-fruited fruiting plant species growing in a 1-ha plot of planted Pinus thunbergii in central Japan. We tested whether the numbers of seeds and seed species dropped by birds beneath fruiting plants were correlated with the number of fruits removed by birds from the plants. Most of fruiting plant species with high fruit removal had significantly high seed rain. Both the numbers of seeds and seed species dropped were significantly, positively correlated with the number of fruits removed across for all fruiting plant species. Therefore, fruit removal predicted the difference among heterospecific fruiting plants in seed rain. We also tested whether the number of fruits removed from fruiting plants by birds was related with fruit crop size, fruit size, and height of the plants, and the numbers of fruits and fruit species of neighboring plants near the plants. Most of fruiting plant species with high fruit crop size had significantly high fruit removal. The number of fruits removed was significantly, positively correlated with both the fruit crop size and the number of neighboring fruits across the nine fruiting plant species. However, the effect of the neighboring fruit density on fruit removal was lower remarkably than that of fruit crop size. Therefore, fruit crop size best predicted the differences among heterospecific fruiting plants in fruit removal. We suggest that fruiting plant species with high fruit crop size and high fruit removal contribute to intensive seed rain beneath them. This revised version was published online in June 2006 with corrections to the Cover Date.     

Analysis of wood thrush (<Emphasis Type="Italic">Hylocichla mustelina</Emphasis>) movement patterns to explain the spatial structure of American ginseng (<Emphasis Type="Italic">Panax quinquefolius</Emphasis>) populations

American ginseng (Panax quinquefolius) is America’s premier wild-harvested, medicinal plant that inhabits the forest understory of eastern deciduous forests. Recent research revealed that birds, particularly wood thrushes (Hylocichla mustelina), disperse ginseng seeds by regurgitating viable seeds 15–37 min after consuming the berries. We carried out two studies to examine the potential effect of thrushes on spatial dispersion patterns of ginseng. First, to analyze how far wood thrushes could disperse seeds, two wood thrushes were outfitted with radio transmitters and tracked for multiple days. Second, for 28 natural populations of ginseng, we created a clustering index to quantify to what degree populations were structured into spatially separated units. To further detect spatial impacts of thrushes, we analyzed inter-cluster distances and the overall spread of ginseng populations. Over the time period in which wood thrushes retain ginseng in their guts, the seeds would be dispersed a mean distance of 15.2–21.7 m. The observed distances ranged from 0–96.6 m. These distances were comparable to the overall spread metric for ginseng populations with wood thrushes, which had increased spacing in comparison to those without wood thrushes. The mean dispersion index differed for populations with and without wood thrushes. It is imperative to understand the interaction between wood thrushes and ginseng to facilitate conservation, as both species are experiencing population declines. Dispersal of seeds by wood thrushes could play an important role in allowing species such as ginseng to respond to climate change, deer browse, overharvesting, and other environmental stresses.     

Seed size selection by olive baboons

Seed size is an important plant fitness trait that can influence several steps between fruiting and the establishment of a plant’s offspring. Seed size varies considerably within many plant species, yet the relevance of the trait for intra-specific fruit choice by primates has received little attention. Primates may select certain seed sizes within a species for a number of reasons, e.g. to decrease indigestible seed load or increase pulp intake per fruit. Olive baboons (Papio anubis, Cercopithecidae) are known to select seed size in unripe and mature pods of Parkia biglobosa (Mimosaceae) differentially, so that pods with small seeds, and an intermediate seed number, contribute most to dispersal by baboons. We tested whether olive baboons likewise select for smaller ripe seeds within each of nine additional fruit species whose fruit pulp baboons commonly consume, and for larger seeds in one species in which baboons feed on the seeds. Species differed in fruit type and seed number per fruit. For five of these species, baboons dispersed seeds that were significantly smaller than seeds extracted manually from randomly collected fresh fruits. In contrast, for three species, baboons swallowed seeds that were significantly longer and/or wider than seeds from fresh fruits. In two species, sizes of ingested seeds and seeds from fresh fruits did not differ significantly. Baboons frequently spat out seeds of Drypetes floribunda (Euphorbiaceae) but not those of other plant species having seeds of equal size. Oral processing of D. floribunda seeds depended on seed size: seeds that were spat out were significantly larger and swallowed seeds smaller, than seeds from randomly collected fresh fruits. We argue that seed size selection in baboons is influenced, among other traits, by the amount of pulp rewarded per fruit relative to seed load, which is likely to vary with fruit and seed shape.     

The fruits of selectivity: how birds forage on Goupia glabra fruits of different ripeness

Although many studies have been published on avian fruit selection, few have addressed the effects of fruit scarcity on the patterns of fruit choice. Here, we compared the consumption of seven bird species for six simultaneously present maturation stages of Goupia glabra fruits. Ripe G. glabra fruits contain more lipids, carbohydrates and energy, and fewer phenols, than unripe fruits. All bird species selected from among ripening stages and removed a higher proportion of ripe fruits than of intermediate or unripe fruits. Importantly, however, fruit choice was flexible in all species. Whether birds preferred or avoided fruits of intermediate ripeness depended on the overall fruit supply. When ripe fruits were scarce, birds showed a higher acceptance of fruits of intermediate ripeness, but still rejected the least ripe fruit stages. In a foraging bout, most birds fed on fruits of the same ripeness. By doing so, birds maximised instantaneous energy gain per time, because search time was longer for riper fruits while energy intake was lower for less ripe fruits. The results suggest that birds select fruits based on fine-scale differences in profitability, but accept less profitable fruits during low fruit abundance. If environmental factors such as overall fruit availability influence avian fruit choice, we suggest that the potential for directional selective pressures on fruit compounds is restricted.     

Seed-eating by West African cercopithecines, with reference to the possible evolution of bilophodont molars

Data on tooth use in eating fruits and seeds were collected on 12 West African monkeys representing five species of cercopithecines, Cercopithecus aethiops, Cercopithecus campbelli, Cercocebus atys, Erythrocebus patas, and Papio papio. Field observations and information in the published literature were used to select fruits for captive feeding trials. A total of over 27,000 tests were conducted to determine the preferences of the monkeys for 78 fruits. Data were collected on the selection of fruit parts, as well as tooth use, in eating 88 fruit species. All five monkey species had remarkably similar fruit part preferences. Seeds were eaten in 86% of the tested fruits and represent the fruit part most frequently eaten by all the tested monkeys. With few exceptions, molars were used to puncture and crush the seeds. It is suggested that the development of bilophodont molars might be an adaptation by Old World monkeys to seed predation. Given their large size relative to other arboreal frugivores, seed predation could provide a dietary niche for Old World monkeys.