Commuting fruit bats beneficially modulate their flight in relation to wind

When animals move, their tracks may be strongly influenced by the motion of air or water, and this may affect the speed, energetics and prospects of the journey. Flying organisms, such as bats, may thus benefit from modifying their flight in response to the wind vector. Yet, practical difficulties have so far limited the understanding of this response for free-ranging bats. We tracked nine straw-coloured fruit bats (Eidolon helvum) that flew 42.5 ± 17.5 km (mean ± s.d.) to and from their roost near Accra, Ghana. Following detailed atmospheric simulations, we found that bats compensated for wind drift, as predicted under constant winds, and decreased their airspeed in response to tailwind assistance such that their groundspeed remained nearly constant. In addition, bats increased their airspeed with increasing crosswind speed. Overall, bats modulated their airspeed in relation to wind speed at different wind directions in a manner predicted by a two-dimensional optimal movement model. We conclude that sophisticated behavioural mechanisms to minimize the cost of transport under various wind conditions have evolved in bats. The bats’ response to the wind is similar to that reported for migratory birds and insects, suggesting convergent evolution of flight behaviours in volant organisms.     

Ethanol ingestion affects flight performance and echolocation in Egyptian fruit bats

Ethanol, a potential toxin for vertebrates, is present in all fleshy fruits and its content increases as the fruit ripens. Previously, we found that the marginal value of food for Egyptian fruit bats, Rousettus aegyptiacus, decreases when its ethanol content exceeds 1%. Therefore, we hypothesized that, if ingested, food containing >1% ethanol is toxic to these bats, probably causing inebriation that will affect flight and echolocation skills. We tested this hypothesis by flying Egyptian fruit bats in an indoor corridor and found that after ingesting ethanol-rich food bats flew significantly slower than when fed ethanol-free food. Also, the ingestion of ethanol significantly affected several variables of the bats’ echolocation calls and behavior. We concluded that ethanol can be toxic to fruit bats; not only does it reduce the marginal value of food, but it also has negative physiological effects on their ability to fly competently and on their calling ability.     

Reproduction elevates the corticosterone stress response in common fruit bats

Changes in reproductive state or the environment may affect the sensitivity of the hypothalamic-pituitary-andrenal (HPA) axis. However, little is known about the dynamics of the resulting corticosteroid stress response, in particular in tropical mammals. In this study, we address the modulation of corticosterone release in response to different reproductive conditions and seasonality in 326 free-living common fruit-eating bats (Artibeus jamaicensis) on Barro Colorado Island in Panama during dry and wet seasons. We present strong evidence that stress sensitivity is primarily modulated by reproductive condition. In reproductively active females, corticosterone increases were more rapid and reached higher levels, but also decreased significantly faster than in inactive females. The corticosterone response was weaker in reproducing males than in females and delayed compared to non-reproductive males. Testes volume in reproductively active males was negatively correlated with corticosterone concentrations. Our findings suggest differentiated dynamics in the corticosterone stress response between sexes, potentially reflecting conflicting ecological demands. In females, a strong acute corticosterone response may represent high stress- and risk-sensitivity that facilitates escape and thus helps to protect reproduction. In males, suppression during reproductive activity could reflect lowered stress sensitivity to avoid chronically elevated corticosterone levels in times of frequent aggressive and therefore costly inter-male encounters.     

The flight of pipistrelle bats Pipistrellus pipistrellus during pregnancy and lactation

A group of 20 pipistrelle bats were taken into captivity and allowed free flight and association within a flight room where they gave birth to and successfully reared 17 young. The flight of the females was recorded during pregnancy, early lactation and post-lactation by using stroboscopic stereophotogrammetry (153 flights reconstructed in total). During the investigation body mass was altering owing to reproductive condition, and changes in mass were recorded daily for all (adult and juvenile) bats during the entire study period, which lasted from two weeks before the last birth until release, when the oldest baby was 43 days old. All bats were individually marked, and detailed morphological measurements were made. Pregnant and post-lactating bats were heavier than lactating bats, which showed the lowest wingbeat frequencies. The flight speeds of pregnant, lactating and post-lactating bats showed no significant differences, and this may be because the pregnant bats appeared to have a wider scope for selecting flight speed than the other two reproductive groups, or than animals studied previously. The group of bats as a whole decreased flight speed (scaling as M^-043) and increased wingbeat frequency (scaling as M^0.58) as their mass increased. Wingbeat amplitude showed no relation to body mass, wing area or span, flight speed or frequency. A flight performance model applied to the experimental results and optimum flight conditions is used to predict cost of transport and mechanical power for steady flight, and equilibrium wingbeat amplitude which is compared with observations.     

Migratory flight imposes oxidative stress in bats

Many animal species migrate over long distances, but the physiological challenges of migration are poorly understood. It has recently been suggested that increased molecular oxidative damage might be one important challenge for migratory animals. We tested the hypothesis that autumn migration imposes an oxidative challenge to bats by comparing values of 4 blood-based markers of oxidative status (oxidative damage and both enzymatic and nonenzymatic antioxidants) between Nathusius' bats Pipistrellus nathusii that were caught during migration flights with those measured in conspecifics after resting for 18 or 24 h. Experiments were carried out at Pape Ornithological Station in Pape (Latvia) in 2016 and 2017. Our results show that flying bats have a blood oxidative status different from that of resting bats due to higher oxidative damage and different expression of both non enzymatic and enzymatic antioxidants (glutathione peroxidase). The differences in oxidative status markers varied betwee n sampli ng years and were in depende nt from in dividual body con dition or sex. Our work provides evidence that migratory flight might impose acute oxidative stress to bats and that resting helps animals to recover from oxidative damage accrued en route. Our data suggest that migrating bats and birds might share similar strategies of mitigating and recovering from oxidative stress.     

Control of the annual cycle in birds: endocrine constraints and plasticity in response to ecological variability

This paper reviews information from ecological and physiological studies to assess how extrinsic factors can modulate intrinsic physiological processes. The annual cycle of birds is made up of a sequence of life-history stages: breeding, moult and migration. Each stage has evolved to occur at the optimum time and to last for the whole duration of time available. Some species have predictable breeding seasons, others are more flexible and some breed opportunistically in response to unpredictable food availability. Photoperiod is the principal environmental cue used to time each stage, allowing birds to adapt their physiology in advance of predictable environmental changes. Physiological (neuroendocrine and endocrine) plasticity allows non-photoperiodic cues to modulate timing to enable individuals to cope with, and benefit from, short-term environmental variability. Although the timing and duration of the period of full gonadal maturation is principally controlled by photoperiod, non-photoperiodic cues, such as temperature, rainfall or food availability, could potentially modulate the exact time of breeding either by fine-tuning the time of egg-laying within the period of full gonadal maturity or, more fundamentally, by modulating gonadal maturation and/or regression. The timing of gonadal regression affects the time of the start of moult, which in turn may affect the duration of the moult. There are many areas of uncertainty. Future integrated studies are required to assess the scope for flexibility in life-history strategies as this will have a critical bearing on whether birds can adapt sufficiently rapidly to anthropogenic environmental changes, in particular climate change.     

Wood mice aggressiveness and flight response to human handling: Effect of individual and environmental factors

Numerous studies have examined human disturbance repercussions on wildlife, mainly focused on the effects on behaviour, reproductive success and population dynamics. However, few studies have addressed the behaviour of prey species during and after human capture and handling and how this may correlate to individual characteristics or variation in their physical environment they inhabit. We explored wood mouse’s fleeing and aggressive behaviours in response to captures by human in their natural habitat. Eighty‐seven wood mice were caught using Sherman live traps. For each trapped individual, aggressiveness was measured as the total number of bites inflicted upon the investigator during handling time. Afterwards, each mouse was released in a two‐metre radius partially covered vegetation area that allowed visual mouse tracking by the observer and flight behaviour was registered by individual one‐zero focal sampling technique during 2 min. Both aggressiveness and fleeing behaviour were analysed regarding individual (sex, reproductive status, age) and environmental factors (habitat and season). Males, adults and breeding individuals showed heightened aggression levels. Higher aggressiveness levels were found in wood mice occupying scrubland and during summer and autumn. The flight response was exclusively explained by reproductive status, whereby breeding individuals spent more time on fast escape than nonbreeding ones. These results indicate that both individual and environmental factors seem to influence defensive behaviours in the wood mouse during and after being captured by a human. Since human disturbance shares many aspects with the predation risk, behavioural responses found to captures may likely be influenced by previous experience of individuals with predators as well as to seasonal and habitat features conditioning predators’ densities but also protection against them.     

Sunset-related timing of flight activity in neotropical bats

Summary The times of onset and completion of the hunting flights of three colonies of neotropical bats, each comprising 100–200 individuals, were observed for nine months. The colonies were of different species: Molossus ater (M.a.) and Molossus molossus (M.m.) of the Molossidae, and Myotis nigricans (My. n.) of the Vespertilionidae. Individuals of Phyllostomus hastatus (P.h., Phyllostomidae) were also observed. All the bats roosted in a building near Restrepo, Colombia (4°16N, 73°34W). Times of emergence in the evening and the return of the last animals in the morning were recorded on 2 to 3 successive days each month. For all bats, the emergence time changed in parallel with that of sunset, and the return paralleled sunrise (Fig. 1). Accordingly, the duration of the activity period is positively correlated with the duration of the night. No annual periodic changes in phase (re sunset/sunrise) of the onset and end of flight activity could be demonstrated, but there was a close relationship between the timing of activity and particular light intensities during twilight (Fig. 4). The first flyers of M.a. appear at the highest intensity (30–300 lx) and those of My. n. at the lowest (0.1–5 lx); the last flyers to return appear in the opposite sequence. For each species, the return to the roost usually occurs at a lower intensity than the departure. These findings, made with four neotropical bat species, differ from those of Subbaraj and Chandrashekaran (1977) with the emballonurid bat Taphozous that they studied at 9°58 N in India. The ecological factors that may play a role in timing the flight activity of tropical bats are discussed. Sunset-related timing, based on the combined effect of (a) the circadian oscillation in arousal and (b) the transition during twilight to a light-intensity range with reduced inhibition of activity (lightsampling behavior), tends to be the rule in tropical bats; time-of-day-related timing is the exception.Supported by the Deutsche Forschungsgemeinschaft (Er 59/1-3+6)     

Feeding mechanisms in bats: variation within the constraints of flight

By any standard, bats are a successful group of mammals andthe evolution of flight and echolocation were certainly keyinnovations behind their success. That is only part of the story,however. Bats have diversified into trophic niches that rangefrom insectivory to feeding on blood, fruit, or nectar. Whileflight places fundamental constraints on the shape of the postcranialskeleton, skull shape in bats is remarkably diverse. Morphologicalstudies of individual families and sympatric assemblages demonstratethat variation in skull shape is clearly associated with trophicspecialization. Field experiments demonstrate that species-specificbiting behaviors during feeding are common and analyses indicatethat the evolution of cranial morphology and feeding behaviorare correlated. Modeling experiments further suggest that feeding(loading) behaviors and skull shape are functionally linked.If the skulls of bats are under selective pressure for minimalmass because of the energetic demands of flight, then they maybe more "optimized" to meet mechanical demands than are theskulls of other mammals. This would make bats a unique modelsystem for studying the evolution of diversity in skull shapeand its functional implications for the evolution of feedingstrategies in mammals.     

Insect oviposition plasticity in response to host availability: the case of the tephritid fruit fly Bactrocera dorsalis

1. Insect oviposition behaviour is ecologically and physiologically plastic. For tephritid fruit flies, Bactrocera dorsalis Hendel, host availability varies spatially and temporally. Females are expected to adopt adaptive oviposition strategies to maximise lifetime reproductive fitness, including survival. Bactrocera dorsalis oviposition tactics in response to different host availabilities were investigated. 2. This study includes three treatments: (i) variable host densities (host density varied according to a fixed cycle from day to day over values of 1, 5, 10 and 20 hosts per cage), (ii) a fixed high host density (20 hosts per cage), and (iii) a fixed low host density (1 host per cage). 3. Daily egg‐laying number per female over the course of 27 days was entirely independent of host density and highly dependent on female age. As host availability increased, females accepted significantly more hosts, generally laid small egg clutches, and more broadly distributed the eggs. 4. Tephritid fruit flies adaptively adjusted egg clutches in ways that reflected the variability of host availability. Egg‐ and time‐limitation constraints appeared to drive these adjustments. Female egg maturation was triggered by oviposition activity and reflected marked lifetime trade‐offs. Such strategies involved specific time schedules for egg laying. 5.This study defined the oviposition plasticity of the tephritid fruit fly. These results have general implications for the behavioural ecology of insect herbivores and parasitoids.     

Phenotypic plasticity of Daphnia life history traits in response to predator kairomones: genetic variability and evolutionary potential

Cladoceran populations can respond to changingpredation regimes by a phenotypical response as wellas by shifts in genotype frequencies. In this study,we investigated the phenotypic plasticity exhibited bylife history traits of D. galeata in response tothe presence of predator kairomones, as well as theextent to which natural selection may act on thesetraits and their phenotypic plasticity. In alife-table experiment, seven clones of a natural D. galeata population were subjected to kairomonesfrom fish (Perca), from an invertebrate predator(Chaoborus) or a mixture of both. Life historytraits were affected by the kairomones of bothpredators, but effects of Chaoborus wereneutralised by Perca in the kairomone mix. Noapparent trade-off was found between growth- andreproduction related traits: although daphnids fromthe Chaoborus treatment grew faster thandaphnids from the other treatments, no reduction inthe reproductive output was observed. Broad-senseheritabilities were found to be relatively high forsome life history traits (size at maturity, neonatesize, number of neonates) as well as for thephenotypic plasticity response of these traits. Thisreflects the evolutionary potential of life historytraits and their phenotypic response to predatorkairomones in the D. galeata population.Publication number 2334 of The Netherlands Institute of Ecology, Centre for LimnologyPublication number 2334 of The Netherlands Institute of Ecology, Centre for Limnology     

Metabolism during flight in two species of bats, Phyllostomus hastatus and Pteropus gouldii.

The energetic cost of flight in a wind-tunnel was measured at various combinations of speed and flight angle from two species of bats whose body masses differ by almost an order of magnitude. The highest mean metabolic rate per unit body mass measured from P. hastatus (mean body mass, 0.093 kg) was 130.4 Wkg-1, and that for P. gouldii (mean body mass, 0.78 kg) was 69.6 Wkg-1. These highest metabolic rates, recorded from flying bats, are essentially the same as those predicted for flying birds of the same body masses, but are from 2.5 to 3.0 times greater than the highest metabolic rates of which similar-size exercising terrestrial mammals appear capable. The lowest mean rate of energy utilization per unit body mass P. hastatus required to sustain level flight was 94.2 Wkg-1 and that for P. gouldii was 53.4 Wkg-1. These data from flying bats together with comparable data for flying birds all fall along a straight line when plotted on double logarithmic coordinates as a function of body mass. Such data show that even the lowest metabolic requirements of bats and birds during level flight are about twice the highest metabolic capabilities of similar-size terrestrial mammals. Flying bats share with flying birds the ability to move substantially greater distance per unit energy consumed than walking or running mammals. Calculations show that P. hastatus requires only one-sixth the energy to cover a given distance as does the same-size terrestrial mammal, while P. gouldii requires one-fourth the energy of the same-size terrestrial mammal. An empirically derived equation is presented which enables one to make estimates of the metabolic rates of bats and birds during level flight in nature from body mass data alone. Metabolic data obtained in this study are compared with predictions calculated from an avian flight theory.     

Hendra virus infection dynamics in Australian fruit bats

Hendra virus is a recently emerged zoonotic agent in Australia. Since first described in 1994, the virus has spilled from its wildlife reservoir (pteropid fruit bats, or 'flying foxes') on multiple occasions causing equine and human fatalities. We undertook a three-year longitudinal study to detect virus in the urine of free-living flying foxes (a putative route of excretion) to investigate Hendra virus infection dynamics. Pooled urine samples collected off plastic sheets placed beneath roosting flying foxes were screened for Hendra virus genome by quantitative RT-PCR, using a set of primers and probe derived from the matrix protein gene. A total of 1672 pooled urine samples from 67 sampling events was collected and tested between 1 July 2008 and 30 June 2011, with 25% of sampling events and 2.5% of urine samples yielding detections. The proportion of positive samples was statistically associated with year and location. The findings indicate that Hendra virus excretion occurs periodically rather than continuously, and in geographically disparate flying fox populations in the state of Queensland. The lack of any detection in the Northern Territory suggests prevalence may vary across the range of flying foxes in Australia. Finally, our findings suggest that flying foxes can excrete virus at any time of year, and that the apparent seasonal clustering of Hendra virus incidents in horses and associated humans (70% have occurred June to October) reflects factors other than the presence of virus. Identification of these factors will strengthen risk minimization strategies for horses and ultimately humans.     

Mechanisms of natural variability during adaptation of human physiological systems to space flight conditions

Physiological data have been analyzed using the principle of invariant relationships to reveal the mechanisms of adaptive variability. The physicochemical, biochemical, and hormonal blood parameter of the cosmonauts who performed short- and long-term space flights have been used. It has been shown that the application of the methods of fractal geometry to the quantitative estimates of homeostasis allows us to identify the processes depending on the adaptive variability increase/decrease and to determine the state of stability or instability of certain physiological regulatory subsystems, whose mobility and reduction of the level of stability maintain a stable internal structure of relationships throughout the body.     

Echolocation, olfaction and fruit display: how bats find fruit of flagellichorous cucurbits

1. The relationship between plant morphology and the senses used by dispersal agents to find fruit was examined. 'Flagellichory' (fruit borne on pendulous structures), a costly morphology associated with dispersal by bats, is focused on.
2. Using Gurania spinulosa , a flagellichorous vine, and its major dispersal agent, Phyllostomus hastatus , the hypothesis was tested that flagellichory increases the conspicuousness of fruit to bats that use echolocation to find fruit.
3. The responses of wild-caught P. hastatus to various fruiting branch morphologies and fruit odour were recorded. Phyllostomus hastatus used echolocation rather than olfaction to detect fruit, and consistently chose fruit displayed on pendulous leafless branches, ignoring fruit held among leaves on horizontal branches.
4. By comparing echolocation signals with the distance between fruiting branches of G. spinulosa and surrounding vegetation, it was shown that pendulous fruiting branches present clear, clutter-free targets that can be detected by echolocating bats. This is the first demonstration of neotropical frugivorous bats using echolocation to find fruit.