Seasonal changes in the abundance and body condition of honeyeaters (Meliphagidae) in response to inflorescence and nectar availability in the New England National Park,New South Wales

Seasonal changes in numbers and body condition of honeyeaters were examined over 2 years in the New England National Park, New South Wales, Australia. Nectar availability measured as inflorescence density and nectar production were also recorded. In the main study site, the abundance of six of the seven most common species of honeyeater was significantly correlated with inflorescence density. However, honeyeater numbers were not significantly correlated with daily energy productivity. Unlike most honeyeater communities, the New England community was dominated numerically by the Eastern Spinebill, the smallest of the most common species present. Among the most common species, the duration of time a species was recorded in the area was negatively, but not significantly, correlated with its size. All species examined showed similar seasonal changes in body condition, with the highest bodyweights and fat deposits recorded in winter.     

Status and foraging in New Zealand honeyeaters

Abstract

Aggression is a common feature of sociality among nectar-feeding birds, and these have been used to consider many aspects of ecological theory, for example community structure, foraging patterns, social organisation and plant-pollinator systems.

Knowledge of aggression among and within New Zealand's honeyeater species is reviewed. Additional information on the importance of various asymmetric cues as learned predictors of status is considered. High-status individuals appear to gain access to nectar in all situations.

Honeyeaters are monogamous and the relationship between the sexes is examined. Even when mates are not formally associated, both appear to benefit from the presence of the other. Examples of the effect of status on pollination efficiency are also considered.

Workers are urged to consider status and individual differences if we are to increase our understanding of community structure, foraging and plant-pollinator interaction.     

Nectar utilization and pollination by Australian honeyeaters and insects visiting Calothamnus quadrifidus (Myrtaceae)

Nectar availability in Calothamnus quadrifidus flowers was studied at Wongamine Nature Reserve in late spring (November). Despite some overnight depletion by moths and other invertebrates, more nectar was present in flowers at dawn than at the preceding dusk. Significant nectar depletion occurred within a few hours after dawn, mainly due to foraging by two honeyeater species. Lichmera indistincta and Phylidonyris nigra. Thereafter, nectar availability was maintained at relatively low levels, principally because of foraging by honeyeaters and honey bees. Apis mellifera, that became active during the warmer part of the day. Although individual honeyeaters consumed more nectar than A. mellifera, honey bees were so abundant that their total impact was greater than that of either honeyeater species for much of the day. Transfer of C. quadrifidus pollen between flowers is necessary in order to achieve a high level of seed set, as the flowers appear to be protandrous. Honeyeaters appeared to be considerably more significant pollen vectors than A. mellifera.     

Honeyeater foraging: A test of optimal foraging theory

Honeyeaters (Meliphagidae) were observed foraging for nectar from Lambertia formosa inflorescences, each of which has seven flowers. The frequency distribution of numbers of flowers probed per visit to an inflorescence was found to be bimodal, with one peak at two and the other at seven. It is hypothesized that this frequency distribution results from a rule of departure from inflorescences that maximizes the net rate of energy gain. Patterns of nectar distribution were determined for a large sample of inflorescences. In addition the extent to which the honeyeaters re-probe flowers during a visit to an inflorescence was estimated. From these data and from field measurements of the times required by the honeyeaters to perform the various foraging behaviours, computer simulations of honeyeater foraging were constructed. These simulations led in turn to optimal frequency distributions of numbers of flowers probed per inflorescence that were bimodal but had peaks at 1 and 7 instead of 2 and 7. Although the observed and predicted behaviour were consequently similar, the difference between them was nevertheless significant. This difference could have been due to the birds' transient occupancy of the study area.     

Effects of flower removal on abundance and behaviour of honeyeaters in heathland near Sydney

Removal of almost all honeyeater nectar sources from a 5.6 ha area during February to July had no apparent effect on honeyeater nesting or total abundance. Behaviour in the experimental area was also generally unaffected except for the extent of nectar-feeding which was significantly reduced for the most commonly observed species. The honeyeaters must have compensated for the nectar removal by flying to nearby productive areas to feed on nectar. Nectar-removal had no significant effect on the species composition of resident honeyeaters but did affect the species composition of all observed honeyeaters. Nectar removal resulted in a decrease in the abundance of the large and dominant Little Wattlebirds (Anthochaera chrysoptera) and an increase in the abundance of the other, smaller species.     

THE ORIGINS OF ADAPTIVE INTERSPECIFIC TERRITORIALISM

1. In order to understand fully the evolution of a behavioural trait one must not only consider whether it is adaptive in its present environment but also whether it originated as an adaptation to existing selective forces or as a fortuitous consequence of selection for a different role in other environments (i.e., as a pre-adaptation) or of selection for different traits (e.g., as a pleiotropic effect). In this paper interspecific territorialism is examined in species of humming-birds, sun-birds, tropical reef fishes, stingless bees, stomatopods, crayfish, and limpets as a means of determining its adaptiveness and its origins. 2. Humming-birds form complex assemblages with species sorted out among the available resources. Dominant species establish feeding territories where flowers provide sufficient nectar. A few large, dominant species, usually uncommon, are marauders on others' territories. Subordinate species establish territories where flowers are more dispersed or produce less nectar, or they fly a circuit from nectar source to nectar source when flowers are even more dispersed, a foraging pattern called ‘traplining’, or they steal nectar from the territorial species by being inconspicuous while foraging. Two species, Amazilia saucerottei and Selasphorus sasin, subordinate in one-to-one encounters, are able to take over rich resources by establishing several small territories within a territory of a dominant and forcing it to forage elsewhere. 3. Among humming-birds, territorial individuals attacked not only subordinate competitors but marauding humming-birds and some insects, which stayed in the territory and foraged at will, and seemingly inappropriate targets, such as non-competitors. This suggests that the stimulus for aggression is ‘any flying organism near the food resources’, regardless of its appearance. The behaviour rather than the identity of the intruder is the stimulus. 4. Sun-birds resemble humming-birds to the extent that dominants establish territories on rich nectar sources and subordinates establish territories on less rich nectar sources or steal from the territories of dominants. The diversity of foraging patterns is not so great as in humming-birds, perhaps because so few species of sun-birds have been studied. However, the advantage of territorialism has been measured in the sun-bird Nectarinia reichenowi. Individuals with territories lose much less nectar to competitors than do those without territories. 5. Field work on three species of tropical reef fishes involved a single aggressive species whose individuals attacked a wide range of species intruding on their territories. The stimulus for aggression in Pomacentrus jenkinsi seemed to be an “object moving through [its] territory”. As suggested for humming-birds, the stimulus is the behaviour rather than the identity of the intruder. 6. The relationships found in stingless bees, stomatopods, crayfish, and limpets are simpler. The dominant and subordinate species divide the resources in their habitat, the dominants' aggression preventing the subordinates from using resources that were otherwise available to them. 7. A general pattern emerges. Mutual interspecific territorialism occurs between species that (i) have different geographic ranges, (ii) occupy different habitats, or (iii) use different resources within the same habitat. Examples of two species holding separate territories on the same resources within the same habitat are rare and occur when the dominant species is rare relative to the available resources. These observations are contrary to the usual view that interspecific territorialism is an adaptation that permits co-existence of potential competitors within the same habitat. 8. Interspecific territorialism is sometimes adaptive and sometimes maladaptive, depending upon the species and the situation. 9. The general pattern of occurrence of the behaviour and the general nature of the stimulus for aggression, i.e., the behaviour rather than the identity of the intruder, suggest that interspecific territoriality is a fortuitous consequence of selection for intraspecific territorialism, the latter being not only an adaptation to the presence of conspecific competitors but a pre-adaptation to the presence of competitors of other species, should they occur.     

Partitioning of nectar sources in an Australian honeyeater community

Feeding by honeyeaters was found to maintain nectar at low levels at three sites studied on Kangaroo Island in May-June 1978. The productivity of nectar at a site and position in a dominance hierarchy appeared to determine which bird species used each site. Correa was the main nectar source in the poorest area and produced 0.05 kJ m^?2 per day. The small eastern spinebill was the most abundant honeyeater. The purple-gaped honeyeater also occurred but fed mostly on honeydew. The medium sized New Holland honeyeater was common and territorial in the second area, where Banksia marginata and B. ornata inflorescences and Adenanthos flowers produced 0.7 kJ m^?2 of nectar per day. Spinebills and crescent honeyeaters also visited flowers and were sometimes chased by New Holland honeyeaters. The richest site was a flowering Eucalyptus cosmophylla tree (5.1 kJ m^?2 of nectar per day). A red wattlebird, the largest honeyeater, held a territory in part of this tree and chased other honeyeaters from the territory. New Holland, crescent and purple-gaped honeyeaters fed on flowers in other parts of the tree. The spinebill was absent. We conclude that nectar was partitioned along a spectrum of rich to poor sources. Larger more aggressive species used and sometimes defended the richest sources while the smaller birds used the poorer sources.     

Competition for nectar resources does not affect bee foraging tactic constancy

1. Competition alters animal foraging, including promoting the use of alternative resources. It may also impact how animals feed when they are able to handle the same food with more than one tactic. Competition likely impacts both consumers and their resources through its effects on food handling, but this topic has received little attention. 2. Bees often use two tactics for extracting nectar from flowers: they can visit at the flower opening, or rob nectar from holes at the base of flowers. Exploitative competition for nectar is thought to promote nectar robbing. If so, higher competition among floral visitors should reduce constancy to a single foraging tactic as foragers will seek food using all possible tactics. To test this prediction, field observations and two experiments involving bumble bees visiting three montane Colorado plant species (Mertensia ciliata, Linaria vulgaris, Corydalis caseana) were used under various levels of inter- and intra-specific competition for nectar. 3. In general, individual bumble bees remained constant to a single foraging tactic, independent of competition levels. However, bees that visited M. ciliata in field observations decreased their constancy and increased nectar robbing rates as visitation rates by co-visitors increased. 4. While tactic constancy was high overall regardless of competition intensity, this study highlights some intriguing instances in which competition and tactic constancy may be linked. Further studies investigating the cognitive underpinnings of tactic constancy should provide insight on the ways in which animals use alternative foraging tactics to exploit resources.     

Resource Partitioning by Mangrove Bird Communities in North Australia

Mangrove bird communities in north Australia comprise relatively few passerine species compared with other arboreal habitats in the region. Mangroves are dominated by a few tree species and there are potentially few resource axes available for partitioning by terrestrial birds. Competition for limited resources is predicted to cause strong niche differentiation and a highly structured, but low diversity, bird assemblage. Using multivariate and bipartite network analyses based on 1771 foraging observations (33% of 5320 behavioral observations), we examined resource partitioning by 20 terrestrial bird species in mangroves of north Australia. The mangrove bird community largely comprised generalist insectivores that partitioned insects by size with moderate‐to‐high interspecific overlap in diet. Gleaning for insects was the most common foraging mode. Few species specialized on nectar. Flowers of one or more mangrove species were available in every month of the year and insect abundance was correlated with flowering peaks. Niche differentiation by birds was determined by food type and foraging mode more than by broad spatial (mangrove zones) or temporal (seasonal) segregation of the use of resources. There was little evidence of bird species saturation or species sorting, suggesting loose species packing and a lesser role than expected for species interactions and interference competition in structuring the bird assemblage in mangroves.     

Extensive consumption of Tabebuia aurea (Manso) Benth. & Hook. (Bignoniaceae) nectar by parrots in a Tecoma savanna in the southern Pantanal (Brazil).

Neotropical parrots forage for various food items such as seeds, fruit pulp, flowers, young leaves, and even arthropods. While foraging, many species wander over large areas that include both open and closed habitats. In this study, I examined parrot foraging activity during a brief synchronous and massive flowering in August 1998 in a tecoma savanna (dominated by Tabebuia aurea) in the southern Pantanal. Six parrot species, ranging from the small Brotogeris chiriri to the large Amazona aestiva, foraged for T. aurea nectar, but Nandayus nenday was by far the major nectar consumer, and the results of each of their visits, like those of the other species, was damage of a substantial proportion of the existing flower crop. Parrots foraged mostly during the afternoon, when nectar concentration tended to be higher. Nevertheless, compared to bird-pollinated flowers, which produce copious nectar, T. aurea had a smaller mean nectar volume per flower. Hence, presumably the amount of damage wreaked by these parrots resulted from their efforts to obtain part of their daily energy and water requirements. Thus, the synchronous and massive flowering occurring in such a brief period in the dry season may be related to, among other factors, the necessity of satiating predators such as parrots, which are still abundant in the Pantanal.     

Competition Between Distantly Related Taxa In the Coevolution of Plants and Pollinators

Competition among distantly related plants for pollinators andamong distantly related animals for pollen and nectar playsa potentially important role in the organization of ecologicalcommunities and the coevolution of plant-pollinator relationships.Plants which rely on animals to disperse their pollen potentiallycompete for pollinators by processes similar to interferenceand exploitative competition. Coexisting plant species may evolveto avoid or reduce such competition by character displacementin floral morphology and/or phenology. One important differencebetween competition for pollinators and most other kinds ofcompetition is that pollinator resources are not used up andmade absolutely unavailable to competitors. Consequently, plantspecies can potentially overlap completely in their utilizationof pollinators. The disadvantages of competing apparently aresometimes outweighed by the advantages of sharing pollinators,because distantly related plant species frequently show evolutionaryconvergence in floral morphology, blooming time and nectar rewardsto utilize the same pollinators. Distantly related animal taxa may compete for floral nectarand pollen by both interference and exploitation. The mechanismsof such competition depend primarily on the energetic costsand benefits of foraging and aggression. Exploitative competitionis very important because nectar feeders of small body sizeand low energy requirements can forage economically and reducenectar availability to levels that will not support larger animals.Thus small nectarivores often can exclude larger competitorsfrom flowers to which both taxa have equal access. Plants mayevolve to influence the outcotre of competition among animalvisitors and favor species that provide the best pollinationservices. Thus flowers specialized for pollination by largeanimals often show morphological or phenological specializationswhich make rewards unava'lable to smaller animals. Interferenceis adaptive only when the benefits of exclusive use of a resourceoutweig.i the costs of defending it. Because distantly relatedkinds of flower visitors often differ in body size and energeticrequirements, interference competition among them is probablyrare although it is often important among closely related nectarivores. The community level consequences of competition in the ecologyand evolution of plant-pollinator associations are still poorlyunderstoood. Competition among distantly related pollinatorsfor plant floral rewards appears to play a major role, but competitionamong plants for pollinator services may be only a weak force.Although the basic interaction between plant and pollinatorusually is a mutualistic one, certain species of both plantsand animals parasitize this interaction and compete with themutualists for limited resources. Thus some animals rob nectarand pollen and compete with legitimate pollinators without providingpollination services. Similarly, some plants offer no floralrewards but obtain pollinator services by mimicing rewardingflowers of other species. The effects of these kinds of interactionson the organization of communities of plants and pollinatorsprovide a fertile area for future research.     

Determinants of foraging profitability in two nectarivorous butterflies

ABSTRACT.

• 1 I studied flower selection and foraging energetics of Agraulis vanillae L. (Nymphalidae) and Phoebis sennae (Pieridae), two butterfly species common to north central Florida. I identified the major nectar resources exploited by several populations of these butterflies and, for each plant species, measured available nectar volumes and concentrations, corolla lengths, and density. I quantified foraging behaviour of each butterfly species at each nectar source (flower visitation rate and percentage of foraging time in flight), and used these data to estimate the net rate of energy intake of each butterfly species at each nectar source.
• 2 Estimated mean energy contents of individual flowers of the eleven exploited plant species spanned three orders of magnitude, ranging between 0.015 and 9.27 joules. Mean energy content of individual flowers was strongly correlated with mean foraging profit of both butterfly species.
• 3 Mean nectar volume strongly influenced energy content and varied widely within and among species, ranging from 0.0076 to 1.853 μ1. Nectar concentration varied between 17.1% and 40.4% sucrose-equivalents. Nectar volume was the best single predictor of foraging profitability (correlation coefficients of 0.994 and 0.984 for Phoebis and Agraulis respectively). Corolla length also strongly affected foraging profitability for both butterfly species; flower species with longer corollas were generally more profitable.
• 4 Flower density and nectar concentration showed weak or nonsignificant associations with foraging profitability.
• 5 The usefulness and limitations of these floral characteristics as bases for foraging selectivity, and the selective pressures foraging butterflies might place on the visited plants are discussed.

     

Models of optimal foraging and resource partitioning: deep corollas for long tongues

We model the optimal foraging strategies for 2 nectarivore species,differing in the length of their proboscis, that exploit thenectar provided by 2 types of flowers, differing in the depthsof their corollas. When like flowers appear in clumps, nectarivoresmust decide whether to forage at a patch of deep or shallowflowers. If nectarivores forage optimally, at least one flowertype will be used by a single nectarivore species. Long-tonguedforagers will normally visit deep flowers and short-tonguedforagers shallow flowers, although extreme asymmetries in metaboliccosts may lead to the opposite arrangement. When deep and shallowflowers are randomly interspersed, nectarivores must decide,on encounter with a flower, whether to collect its nectar orcontinue searching. At low nectarivore densities, the optimalstrategy involves exploiting every encountered flower; however,as nectarivore densities increase and resources become scarce,long-tongued individuals should start concentrating on deepflowers and short-tongued individuals on shallow flowers. Therefore,regardless of the spatial distribution of flowers, corolla depthcan determine which nectarivore species exploit the nectar fromeach flower type in a given community. It follows that corollaelongation can evolve as a means to keep nectar thieves at bayif short-tongued visitors are less efficient pollinators thanlong-tongued visitors.     

Observational Learning in the White-Eared Hummingbird (Hylocharis leucotis): Experimental Evidence

The adoption of new food resources can be facilitated by the ability to learn through observation of other individuals who use them. This behavior, termed observational learning, applies to any problem solving in which a naive individual who has observed an experienced individual learns a behavior faster than another who has not. Hummingbirds consume nectar from flowers of a large number of plant species, which are very diverse in morphology and color. During their local or migratory movements, they can observe the use of floral resources by conspecifics and heterospecifics which may change their foraging preferences. Although there is evidence that hummingbirds can use observational learning to exploit new floral resources, it is necessary to generate additional information by studying different hummingbird species. In this work, the learning performance of White‐eared hummingbirds (Hylocharis leucotis) was studied in the presence or absence of a knowledgeable tutor. In a first experiment, naïve hummingbirds learned to feed on arrays of artificial flower of two colors: red (previously known resource) and yellow (novel resource), where only one color had nectar. Naive hummingbirds visited red flowers faster and more often than rewarded yellow flowers. Individuals with the best performance on each color were further trained to ensure that they only visited flowers of a specific color, and were then used as tutors in the next experiment, in which new naive hummingbirds, caged individually, were allowed to observe them foraging on the artificial arrays. These naïve individual were then exposed alone to the same array used by their tutor. Tutored hummingbirds learned to feed faster and more frequently from nectar‐containing flowers of the array than naive individuals. Likewise, all tutored individuals only visited flowers of the color that had been previously visited by their tutors. This study provides experimental evidence that hummingbirds taken directly from the field can use observational learning as an efficient strategy to access new floral resources.     

Extrafloral‐nectaries and interspecific aggressiveness regulate day/night turnover of ant species foraging for nectar on Bionia coriacea

Plants bearing extrafloral nectaries (EFNs) vary the secretion of nectar between day and night, which creates turnover in the composition of interacting ant species. Daily variation in the composition of ant species foraging on vegetation is commonly observed, but its mechanisms are poorly understood. We evaluated the daily variation in nectar availability and interspecific aggressiveness between ants as possible regulatory mechanisms of the turnover in ant–plant interactions. We hypothesized that (i) plants would interact with more ant species during periods of higher secretion of nectar and that (ii) aggressive ant species would compete for nectar, creating a daily turnover of species collecting nectar. We tested this hypothesis by measuring the production of nectar during the day and night and by experimentally removing EFNs of Bionia coriacea (=Camptosema coriaceum) (Nees & Mart.) Benth. (Fabaceae: Faboideae) plants in a Brazilian savanna (Cerrado). We then compared the abundance and composition of ant species between those treatments and during the day. Our results indicate that more ant workers forage on plants during the day, when nectar was sugary, while more ant species forage at night, when aggressiveness between ant species was lower. We also detected a day/night turnover in ant species composition. Ant species foraging for nectar during the day were not the same at night, and this turnover did not occur on plants without EFNs. Both dominant ant species, diurnal Camponotus crassus (Hymenoptera: Formicidae) and nocturnal Camponotus rufipes (Hymenoptera: Formicidae), were the most aggressive species, attacking other ants in their specific periods of forage while also being very aggressive toward each other. However, this aggressiveness did not occur in the absence of nectar, which allowed non‐aggressive nocturnal ant species to forage only during the daytime, disrupting the turnover. We conclude that extrafloral‐nectar presence and interspecific aggressiveness between ants, along with other environmental factors, are important mechanisms creating turnovers in ants foraging on plants.     

Bottom-up control and co-occurrence in complex communities: honeydew and nectar determine a rainforest ant mosaic

Complex distribution patterns of species-rich insect communities in tropical rainforests have been intensively studied, and yet we know very little about processes that generate these patterns. We provide evidence for the key role of homopteran honeydew and plant nectar in structuring ant communities in an Australian tropical rainforest canopy and understorey. We also test the ant visitation of these resources against predictions derived from the 'ant-mosaic' hypothesis. Two ant species were highly dominant in terms of territorial behaviour and abundance: Oecophylla smaragdina and Anonychomyrma gilberti . Both dominant ant species monopolised large aggregations of honeydew-producing homopterans. Attended homopteran species were highly segregated between these two ant species. For the use of extrafloral and floral nectar (involving 43 ant species on 48 plant species), partitioning of ant species among plant species and between canopy and understorey was also significant, but less pronounced. In contrast to trophobioses, simultaneous co-occurrence of different nectar foraging ant species on the same plant individuals was frequent (23% of all surveys). While both dominant ant species were mutually exclusive on honeydew and nectar sources, co-occurrence with non-dominant ant species on nectaries was common. The proportion of visits with co-occurrences was low for dominant ants and high for many sub-ordinate species. These findings support the ant mosaic theory. The differential role of honeydew (as a specialised resource for dominant ants) and nectar (as an opportunistic resource for all ants including the co-occurring non-dominant species) provides a plausible structuring mechanism for the Australian canopy ant community studied.     

The foraging profile of a wandoo woodland avifauna in early spring

Abstract This study reports on the foraging profile of a wandoo woodland avifauna at Dryandra in Western Australia, Australia. Despite its geographical isolation, wandoo woodland shares a large number of species with woodland bird communities in eastern Australia and there are broad similarities in community foraging profiles. Insect-eating birds using ground, bark, foliage, and aerial substrates dominate eucalypt bird communities. Nectar-feeding and seed/fruit-eating guilds are important components of the Australian avifauna, but have fewer species, and vary in composition and abundance as nectar, seed, and fruit availability changes seasonally and from year to year, and from one locality to another. Despite similarities, there are also differences between the foraging profile of the wandoo avifauna and those in eastern Australia. Specifically, the wandoo avifauna is characterized by a high proportion of ground-foraging species. In addition, many wandoo woodland birds appear to spread their foraging over a wider range of substrates (i.e., ground, bark, and foliage) than eastern species. Differences in habitat structure do not explain these differences in community foraging profiles, and there may be differences in the abundance, kind, and spatial distribution of resources between different eucalypt ecosystems. Possibly the eastern communities have lost ground-dwelling components of their avifauna since European settlement, while the woodlands at Dryandra retain a more intact avifauna. The reasons why some species and not others are lost from woodlands as a result of European land management practices are discussed.     

Trapline foraging by bumble bees: IV. Optimization of route geometry in the absence of competition

Foraging on resources that are fixed in space but that replenishover time, such as floral nectar and pollen, presents animalswith the problem of selecting a foraging route. What can flowervisitors such as bees do to optimize their foraging routes,that is, reduce return time or route distance? Some repeatedlyvisit a set of plants in a significantly predictable sequence(so-called "trapline foraging"), which may also enhance theirforaging efficiency. A moderate level of optimization and repetitionof foraging routes can be reached by following simple movementrules for choosing the distances and turning angles of successiveflights, without the use of spatial memory. If pollinators canlearn the locations of patches and choose among possible foragingroutes or paths, however, even better performance may be achieved.We tested whether and how bumble bees can optimize and repeattheir foraging routes in laboratory experiments with artificialflowers that secreted nectar at a constant rate. With increasingexperience, foraging routes of bees became more repeatable andefficient than expected from a combination of simple movementrules between successive flowers. We suggest that trapline foragingis a more sophisticated pattern of spatial use than searchingand is based on memory. On the other hand, certain spatial configurationsof flowers hampered optimization by the bees; bees preferredto choose short distances over straight moves and showed littleplasticity in this regard. Developing an efficient trapline,therefore, may require prior selection of a set of plants withan appropriate spatial configuration.     

Relationship between spatial working memory performance and diet specialization in two sympatric nectar bats

Behavioural ecologists increasingly recognise spatial memory as one the most influential cognitive traits involved in evolutionary processes. In particular, spatial working memory (SWM), i.e. the ability of animals to store temporarily useful information for current foraging tasks, determines the foraging efficiency of individuals. As a consequence, SWM also has the potential to influence competitive abilities and to affect patterns of sympatric occurrence among closely related species. The present study aims at comparing the efficiency of SWM between generalist (Glossophaga soricina) and specialist (Leptonycteris yerbabuenae) nectarivorous bats at flowering patches. The two species differ in diet--the generalist diet including seasonally fruits and insects with nectar and pollen while the specialist diet is dominated by nectar and pollen yearlong--and in some morphological traits--the specialist being heavier and with proportionally longer rostrum than the generalist. These bats are found sympatrically within part of their range in the Neotropics. We habituated captive individuals to feed on artificial flower patches and we used infrared video recordings to monitor their ability to remember and avoid the spatial location of flowers they emptied in previous visits in the course of 15-min foraging sequences. Experiments revealed that both species rely on SWM as their foraging success attained significantly greater values than random expectations. However, the nectar specialist L. yerbabuenae was significantly more efficient at extracting nectar (+28% in foraging success), and sustained longer foraging bouts (+27% in length of efficient foraging sequences) than the generalist G. soricina. These contrasting SWM performances are discussed in relation to diet specialization and other life history traits.     

Temporal changes in floral resource availability and flower visitation in a butterfly

Foraging affects survival and reproductive success in animals, including flower-visiting insects. Plant-derived floral food resources (i.e. nectar and pollen) may be rapidly changing in space and time and pollinators may need to quickly switch to new resources. Butterflies are suitable model organisms to investigate foraging behaviour of insect pollinators, because they can be easily monitored under natural conditions. We studied flower visitation patterns in the Clouded Apollo butterfly Parnassius mnemosyne in relation to the abundance of available floral resources. We recorded flower visitation daily in individually marked butterflies, listed flowering species and estimated flower abundance categories every 3 days in a single meadow, during five consecutive flight periods. Butterflies visited 35 nectar plants from the 71 species available. Few nectar plants were frequently visited (visit ratios for the annually most visited species: 37–60%), many were scarcely visited and no visits were observed on several abundant species. Flower abundance and visit ratio varied among years and within flight periods. The number of visits increased with flower abundance in the seven most frequently visited plant species, but not in the occasionally visited ones. Beside their choosiness, Parnassius mnemosyne butterflies were able to adjust foraging behaviour to rapidly changing resource distributions. Diet selectivity in adults might increase the vulnerability of this species. However, visitation plasticity may mitigate the effect of the lack of some nectar plants, as complementary resources can be used as alternatives.