Airborne Insects Research Articles

Monitoring Mosquito Abundance: Comparing an Optical Sensor with a Trapping Method.

Optical sensors have shown significant promise in offering additional data to track insect populations. This article presents a comparative study between abundance measurements obtained from a novel near-infrared optical sensor and physical traps. The optical instrument, named an Entomological Bistatic Optical Sensor System, or eBoss, is a non-destructive sensor operating in the near-infrared spectral range and designed to continuously monitor the population of flying insects. The research compares the mosquito aerial density (#/m3) obtained through the eBoss with trap counts from eight physical traps during an eight-month field study. The eBoss recorded over 302,000 insect sightings and assessed the aerial density of all airborne insects as well as male and female mosquitoes specifically with a resolution of one minute. This capability allows for monitoring population trends throughout the season as well as daily activity peaks. The results affirmed the correlation between the two methods. While optical instruments do not match traps in terms of taxonomic accuracy, the eBoss offered greater temporal resolution (one minute versus roughly three days) and statistical significance owing to its much larger sample size. These outcomes further indicate that entomological optical sensors can provide valuable complementary data to more common methods to monitor flying insect populations, such as mosquitoes or pollinators.

Predictive model for airborne insect abundance intercepted by a continuous wave Scheimpflug lidar in relation to meteorological parameters

A Scheimpflug lidar system, based on the Scheimpflug arrangement has recently been developed and has demonstrated its ability to detect, identify, differentiate, and monitor aerial insect activity in real time and in situ. Despite the performance of such as system, making forecasts remains a challenge. The abundance of aerial insects and their distribution are determined by meteorological factors and seasonality. Based on Scheimpflug lidar data and local meteorological parameters, this study aimed to predict the abundance of airborne insects. Abundance is recorded for both dry and rainy seasons for two days, from 8 am to 9 pm. Local meteorological parameters are also recorded. The exploratory analysis of the meteorological data is carried out using principal component analysis (PCA). Statistical modeling of flying insect activity is carried out using principal, partial least square and ridge regression models. This modeling has shown that the abundance of airborne insects depended largely on the weather conditions and give relevant forecasting of airborne insects to help fighting against vector-borne diseases and to control insect-pests in crops.

Feeding Ecology of Invasive Three-Spined Stickleback (Gasterosteus aculeatus) in Relation to Native Juvenile Eurasian Perch (Perca fluviatilis) in the Pelagic Zone of Upper Lake Constance

The fish community of Lake Constance, a large, deep, oligotrophic lake has undergone drastic changes in recent years, with the sudden rise to dominance of invasive three-spined stickleback (Gasterosteus aculeatus) in the pelagic zone, a rather atypical habitat for this species in Central Europe. The core objective of this study was to compare the feeding ecology of stickleback and young Eurasian perch (Perca fluviatilis) in this unique situation to identify reasons for this unexpected dominance, a possible food niche and feeding time overlap, and to discuss consequences for the reshaped pelagic fish community. The diel feeding patterns and prey compositions of pelagic sticklebacks and juvenile (0+) perch sampled in October 2018 and March 2019 were studied analyzing stomach contents. The diets of both species mostly comprised zooplankton, with copepods appearing in the greatest numbers. Benthic and airborne insects were consumed occasionally, mostly by sticklebacks. Both species exhibited peaks of feeding activity early in the morning, afternoon and dusk, and in both species, stomachs were fullest at dusk. Stickleback stomachs contained about 20% more prey at night than perch, and mean estimated nocturnal stomach fullness values were almost 50% greater. Night feeding in sticklebacks was confirmed by digestive states, pointing to a possible competitive advantage over perch. Dietary composition varied over a 24-h cycle and the pattern of consumption of different prey varied between the species. Perch consumed more comparatively small cladocerans (Bosmina spp.), while larger Daphnia appeared more often in stickleback stomachs. In both species, seasonal variation in diet mirrored food availability, indicating some degree of opportunism. A Morisita-Horn index value of 0.95 confirmed dietary niche overlap between species, suggesting the large population of sticklebacks may exert a competitive effect on juvenile perch when resources are limited. Both the longer feeding periods and greater intake of nutritive high quality prey like daphnids can contribute to the rapid success of stickleback in dominating the pelagic zone of Lake Constance.

Remote-Controlled Monitoring of Flying Pests with an Electrostatic Insect Capturing Apparatus Carried by an Unmanned Aerial Vehicle

The purpose of the study was to construct an electrostatic insect-capturing apparatus that could be applied to a drone (quadcopter). For this purpose, a double-charged dipolar electric field screen (DD-screen) was constructed using oppositely charged insulator tubes that was then attached to a drone. For charging, the inner surface of the tubes was coated with a conductive paste and then linked to a negative or positive voltage generator. The opposite charges of the tubes formed an electric field between them and created an attractive force to capture insects that entered the field. The DD-screen constructed here was sufficiently light to enable its attachment to a drone. The screen was hung from the drone perpendicular to the direction of drone movement, so as to receive the longitudinal airflow produced by the movement of the drone. It was positioned 1.8 m below the drone body to avoid the influence of the downward slipstream generated by the rotating propellers. Eventually, the drone was able to conduct a stable flight, with sufficient endurance, and captured airborne insects carried by an airflow of 8 m/s during the flight. This study, therefore, provides an experimental basis for establishing a new method for conducting trap-based monitoring of airborne insects during remote-controlled flight through operation of a DD-screen attached to a drone.

Low Tunnels Reduce Insect Populations, Insecticide Application, and Chewing Insect Damage on Brussels Sprouts.

Low tunnels covered with spun-bonded fabric (row covers) provide season extension for vegetable production and also afford a physical barrier against airborne insects and other non-soil pests. Brussels sprouts, Brassica oleracea L. group Gemmifera (Brassicaceae), is a popular vegetable in local markets in Virginia; however, unprotected field production is severely affected by insect pest infestation. This study's objective was to determine the level of protection low tunnels provide against insect infestation and leaf herbivory injury. The experiment was conducted at the Virginia Tech Eastern Shore Agricultural Research and Extension Center in Painter, Virginia. The experimental design was split-plot with polyethylene soil mulches (white or black) as whole plot factors and production systems (low tunnel or open field) as subplot factors. In this study, low tunnels reduced insect infestation and chewing herbivory leaf injury to Brussels sprouts. Compared to an unprotected open field, infestations of lepidopteran insects and harlequin bug, Murgantia histrionica (Hahn) (Hemiptera: Pentatomidae) were reduced on plants under low tunnels. However, aphids (Hemiptera: Aphidae) infestation occurred under low tunnels in fall. There was no effect of color mulches (white or black) and no interaction between tunnel and mulch color on insect infestation and chewing injury. Fewer insect infestations and feeding injury indicate that low tunnels can be an effective management tool for sustainable vegetable production.

Integrating Models of Atmospheric Dispersion and Crop-Pest Dynamics: Linking Detection of Local Aphid Infestations to Forecasts of Region-Wide Invasion of Cereal Crops

Abstract Invasive airborne insects pose major challenges in natural resource and agriculture management, as they can rapidly spread over large distances and cross physical boundaries. Field monitoring and local management are important tools to prevent and control infestations but require additional coordination to be operative region-wide. Computational modeling techniques have been effective in simulating local population dynamics and in capturing spread of invasive species on a regional scale. We use an integrated ecological model to simulate local and regional infestation dynamics of sugarcane aphids, Melanaphis sacchari (Zehntner) (Hemiptera: Aphididae), on sorghum, Sorghum bicolor (L.) Moench (family Poaceae), in the southern to central Great Plains of the United States. Local dynamics of aphid populations on sorghum are simulated by a spatially explicit, individual-based model, whereas regional aphid migration is simulated by an atmospheric model that computes inert air particle (aphid) transport, dispersion, and deposition. Simulation results indicate timing of initial infestations in the south affects spatiotemporal patterns of infestation throughout the region. Probability of local infestations is a function of both percentage of land occupied by growing sorghum and prevailing winds. Thus, due to availability of sorghum, relatively later dates of initial infestation in the south will probably lead to infestations farther north that become established more quickly following the first appearance of aphids in the south. The model we present, in coordination with field monitoring schemes, could be applied as a forecasting tool in region-wide pest management systems.

Experimental structural dynamic measurements of an artificial insect-sized wing biomimicking a crane fly forewing

The exceptional flying characteristics of airborne insects motivate the design of biomimetic wing structures that could exhibit a similar structural dynamic behavior. For this purpose, this paper describes methods for manufacturing a biofidelic insect-sized wing using the photolithography technique and analyzing its structural dynamic response in terms of its modal characteristics. The geometry of a crane fly forewing (family Tipulidae) is acquired using a micro-computed tomography scanner. A computer-aided design (CAD) model is generated from the reconstructed scanned model of the insect wing, and a photomask of the venation network that accounts for the stiffness variation along the surface of the insect wing is designed from the CAD model. A composite material artificial insect-sized wing is manufactured by patterning the veins using photoresist SU-8 on a Kapton film for the assembling of the wing. Experiments are performed using a modal shaker and a digital image correlation system to determine the natural frequencies and the mode shapes of the artificial wing from the fast Fourier transform of the time-varying out-of-plane displacement response of the wing. The effect of ultraviolet exposure time to the vein pattern on the modal characteristics of the artificial wing is investigated as a part of a parametric study. The natural frequencies of the wing increase with exposure time. The vibration modes are dominated by a bending and torsional nonlinear deformation response. The experimental results are compared to those predicted by a finite element model of the artificial wing.

Environmental Health Assessment Using Sentinel Species near Placencia Lagoon, Belize

Unexplained bird deaths discovered around Placencia Lagoon, Belize over a 2-year period sparked an investigation into the environmental health of the lagoon and two of its major tributaries. In this study, conducted from January 23 to February 28, 2018, we assessed avian health within two commercial aquaculture facilities, each with a substantial outflow into the lagoon; a shrimp farm and a tilapia farm. Birds were chosen as our study subjects not only because of previous bird deaths, but also as sentinel species to assess overall possible contamination. Both facilities had previously been affected by die-offs of their cultivated product. The variety of sampled bird species, both year-round and winter residents, fed on small fish, airborne insects, mud-dwelling invertebrates and/or plant material, i.e. seeds and fruits, thereby sampling air, soil and water as possible bioaccumulation vectors. We trapped birds in, or nearby outflow containment ponds which emptied into the lagoon. Additionally, we assessed avian health at two reference locations on Placencia Penninsula, not known for avian health problems. Birds from multiple families representing different ecological niches were captured using two net types. We conducted standard ornithological assessments, measured hematocrit, made an evaluation of ectoparasite load and types, and for shorebirds, examined fecal swabs for parasites. Measured values were compared to published data and a previously established database from data collected elsewhere in the Caribbean. For each of the major sites, an extensive period of evaluation was later followed with a shorter, second evaluation at each location. Except for a single, second-year, Brown Pelican (Pelicanus occidentalis) evaluated one day at the close of the study, 257 birds were found to be healthy on all parameters including hematocrit and parasite load. We observed that the pelican had not been present previously and inferred that its health problems were acquired at another site. This conclusion was corroborated by the concurrent discovery of dead or dying pelicans along the Belize coast near the end of this investigation.

Effects of 90Sr on Tree Swallow Nestlings Near Groundwater Contaminant Plumes.

Discharge of groundwater contaminant plumes has created elevated concentrations of Sr in some aquatic sediments at Chalk River Laboratories. Tree swallows (Tachycenita bicolor) feed and supply their nestlings almost exclusively with airborne insects that developed as larvae in aquatic sediments. To monitor the uptake and test for potential detriment due to Sr in a terrestrial animal, we measured the gross beta concentrations in the bone of 12-d-old tree swallow nestlings in areas having sediments with elevated levels of gross beta (Sr and Y) and in several control areas where sediment gross beta was primarily due to naturally occurring K. Nesting behavior and reproductive success of the tree swallows were similar regardless of the gross beta concentrations in sediments near their nest boxes. Radiation can damage DNA and cause micronuclei to form in cells, so we examined the frequency of micronuclei in erythrocytes of nestlings. The formation of micronuclei in the erythrocytes of the nestlings was also similar wherever nestlings were analyzed. The results revealed no significant increases even near sediments with the highest gross beta levels. At Perch Lake, where Chalk River Laboratories has a large area of Sr-contaminated sediments, the bones of 12-d-old nestlings contained gross beta concentrations as high as 29 Bq g. This would produce a skeletal dose rate of 9 μGy h, which is one-fourth of the threshold dose rate of 40 μGy h, above which detriment could occur. Failing to find any indication of detriment in the field study, we irradiated wild eggs in the lab and returned them to their nest for natural incubation, hatching, and feeding by the parents. There was an increase in formation of micronuclei following a dose of 3.2 Gy, and the other results were consistent with existing literature.

Aerial-hawking bats adjust their use of space to the lunar cycle

BackgroundAnimals change their habitat use in response to spatio-temporal fluctuation of resources. Some resources may vary periodically according to the moonphase. Yet it is poorly documented how animals, particularly nocturnal mammals, adjust their use of space in response to the moonphase.Here, we asked if an obligate nocturnal mammal, the aerial-hawking common noctule bat (Nyctalus noctula), adjusts its 3-dimensional flight behaviour and habitat use to the lunar period. Using miniaturized GPS loggers, we recorded 3-dimensional flight tracks of N. noctula and related these to a canopy height model derived from aerial laser scans to investigate whether bats adjust forest strata use to moonlight intensities.ResultsNoctules frequently foraged above the canopy of coniferous forest at low moonlight intensities, but switched to using open grasslands and arable fields in nights with high moonlight intensities. During the few occasions when noctules used the forest during moonlit nights, they mostly restricted their use of space to flying below the canopy level. The median overall flight altitude of N. noctula equalled 13 ± 16 m but reached up to 71 m above ground (97.5% quantile).ConclusionsOur findings argue against general lunar phobic behaviour of aerial-hawking bats. We suggest that the preferred use of open fields around full moon may be a strategy of noctules to increase the success of hunting airborne insects at night. Specifically, the adjustment in use of space may allow bats to hunt for insects that emerge and disperse over open fields during bright moonlight.

Echolocation and flight strategies of aerial-feeding bats during natural foraging

Aerial-feeding bats actively emit sonar sounds and capture large amounts of airborne insects a night. Microphone-array system allows us to know not only the positions where the bat emits sonar sounds (i.e., 3-D flight path) but how the bats dynamically control the acoustical field of view during searching and approaching target-prey. Here, we show echolocation strategy of bats during natural foraging revealed by the large-scale microphone-array system which covered the horizontal area of approximately 20 m × 20 m. Pipistrellus abramus was found to expand the width of their sonar beams in both horizontal and vertical planes just before the prey-capture. Since the bats emit echolocation pulses at a high rate (i.e., feeding buzz) just before capturing, the capture positions can additionally be measured. Recently, we have investigated the relationship between flight patterns, capture positions, and foraging efficiency of Myotis macrodactylus during natural foraging above the pond. Further investigation from the viewpoint of the optimal foraging would reveal echolocation and flight strategies of the bats to efficiently search and approach prey items. [This research was supported by a Grant-in-Aid for Young Scientists (B) and Scientific Research on Innovative Areas of JSPS, and the JST PRESTO program.]

Olfaction in a viscous environment: the "color" of sexual smells in Temora longicornis.

We investigate chemical aspects of mating in the marine copepod Temora longicornis (Copepoda, Calanoidea). Our emphasis is the female pheromone signaling in form of well-defined trails for males to follow, observed in Doall et al. (Phil Trans R Soc Lond B 353:681-689, 1998). The viscous environment and the properties of the odorants play important roles as the spread of the pheromone trail limits the time during which it is useful for tracing. A key observation from our earlier work is the ability of a searching male to detect the direction of the female and to correct its swimming direction if necessary. We propose a simple mathematical model for the spread of a pheromone from a moving source and carry out numerical simulations of two possible detection mechanisms. We find that a searching agent that is capable to detect a ratio outperforms a searcher that depends on the gradient of a single compound. This suggests that copepod sex pheromones consist of blends of chemical compounds, and that a ratio detection mechanism similar to that in airborne insects is at work.

Coordinated Control of Acoustical Field of View and Flight in Three-Dimensional Space for Consecutive Capture by Echolocating Bats during Natural Foraging.

Echolocating bats prey upon small moving insects in the dark using sophisticated sonar techniques. The direction and directivity pattern of the ultrasound broadcast of these bats are important factors that affect their acoustical field of view, allowing us to investigate how the bats control their acoustic attention (pulse direction) for advanced flight maneuvers. The purpose of this study was to understand the behavioral strategies of acoustical sensing of wild Japanese house bats Pipistrellus abramus in three-dimensional (3D) space during consecutive capture flights. The results showed that when the bats successively captured multiple airborne insects in short time intervals (less than 1.5 s), they maintained not only the immediate prey but also the subsequent one simultaneously within the beam widths of the emitted pulses in both horizontal and vertical planes before capturing the immediate one. This suggests that echolocating bats maintain multiple prey within their acoustical field of view by a single sensing using a wide directional beam while approaching the immediate prey, instead of frequently shifting acoustic attention between multiple prey. We also numerically simulated the bats’ flight trajectories when approaching two prey successively to investigate the relationship between the acoustical field of view and the prey direction for effective consecutive captures. This simulation demonstrated that acoustically viewing both the immediate and the subsequent prey simultaneously increases the success rate of capturing both prey, which is considered to be one of the basic axes of efficient route planning for consecutive capture flight. The bat’s wide sonar beam can incidentally cover multiple prey while the bat forages in an area where the prey density is high. Our findings suggest that the bats then keep future targets within their acoustical field of view for effective foraging. In addition, in both the experimental results and the numerical simulations, the acoustic sensing and flights of the bats showed narrower vertical ranges than horizontal ranges. This suggests that the bats control their acoustic sensing according to different schemes in the horizontal and vertical planes according to their surroundings. These findings suggest that echolocating bats coordinate their control of the acoustical field of view and flight for consecutive captures in 3D space during natural foraging.

Strong cascading effect of weather conditions on prey availability and annual breeding performance in European bee-eaters Merops apiaster

Aerial insectivorous birds depend highly on favourable weather conditions for successful foraging because flight activity of insects is constrained by daily weather. Thus, the variation in weather conditions during reproduction, mediated by prey limitations, should be mirrored in annual reproduction performance, and finally in annual breeding success. We analysed the effect of local weather conditions on the availability of airborne insects and on the variation in brood size and nestling condition of European bee-eaters Merops apiaster at the northern edge of their range where years with adverse weather frequently occur. The availability of large flying insects, the common prey of bee-eaters, increased with air temperatures and duration of daily sunshine. As predicted, local weather conditions affected reproductive performance with annual breeding success (mean 3.7 nestlings per breeding pair, range 1.7–4.9 nestlings) being up to 32 % higher in extraordinary dry and hot summers. Additionally, a nestling's body condition (residual mass) was also affected by sunshine duration during their growth period and internally was co-affected by the number of siblings and the individual rank within the sibling hierarchy. Thus, a prolonged duration of daily sunshine causes a cascade from higher insect flight activity, and, thus, higher food availability for chick-rearing bee-eaters, which finally translates into better chick body conditions and higher annual breeding success. Consequently reproduction and population development of European bee-eaters might be especially susceptible to regional changes in weather and climatic conditions.

Dynamics of the echolocation beam during prey pursuit in aerial hawking bats

In the evolutionary arms race between prey and predator, measures and countermeasures continuously evolve to increase survival on both sides. Bats and moths are prime examples. When exposed to intense ultrasound, eared moths perform dramatic escape behaviors. Vespertilionid and rhinolophid bats broaden their echolocation beam in the final stage of pursuit, presumably as a countermeasure to keep evading moths within their "acoustic field of view." In this study, we investigated if dynamic beam broadening is a general property of echolocation when catching moving prey. We recorded three species of emballonurid bats, Saccopteryx bilineata, Saccopteryx leptura, and Rhynchonycteris naso, catching airborne insects in the field. The study shows that S. bilineata and S. leptura maintain a constant beam shape during the entire prey pursuit, whereas R. naso broadens the beam by lowering the peak call frequency from 100 kHz during search and approach to 67 kHz in the buzz. Surprisingly, both Saccopteryx bats emit calls with very high energy throughout the pursuit, up to 60 times more than R. naso and Myotis daubentonii (a similar sized vespertilionid), providing them with as much, or more, peripheral "vision" than the vespertilionids, but ensonifying objects far ahead suggesting more clutter. Thus, beam broadening is not a fundamental property of the echolocation system. However, based on the results, we hypothesize that increased peripheral detection is crucial to all aerial hawking bats in the final stages of prey pursuit and speculate that beam broadening is a feature characterizing more advanced echolocation.

Functional invertebrate prey groups reflect dietary responses to phenology and farming activity and pest control services in three sympatric species of aerially foraging insectivorous birds.

Farming activity severely impacts the invertebrate food resources of farmland birds, with direct mortality to populations of above-ground arthropods thorough mechanical damage during crop harvests. In this study we assessed the effects of phenological periods, including the timing of harvest, on the composition and biomass of prey consumed by three species of aerial insectivorous birds. Common Swifts Apus apus, Barn Swallows Hirundo rustica and House Martins Delichon urbica breed sympatrically and most of their diet is obtained from agricultural sources of invertebrate prey, especially from oil-seed rape crops. We categorized invertebrate prey into six functional groups, including oil-seed rape pests; pests of other arable crops; other crop-provisioned taxa; coprophilous taxa; and taxa living in non-crop and mixed crop/non-crop habitats. Seasonality impacted functional groups differently, but the general direction of change (increase/decrease) of all groups was consistent as indexed by prey composition of the three aerial insectivores studied here. After the oil-seed rape crop harvest (mid July), all three species exhibited a dietary shift from oil-seed rape insect pests to other aerial invertebrate prey groups. However, Common Switfts also consumed a relative large quantity of oil-seed rape insect pests in the late summer (August), suggesting that they could reduce pest insect emigration beyond the host plant/crop. Since these aerially foraging insectivorous birds operate in specific conditions and feed on specific pest resources unavailable to foliage/ground foraging avian predators, our results suggest that in some crops like oil-seed rape cultivations, the potential integration of the insectivory of aerial foraging birds into pest management schemes might provide economic benefits. We advise further research into the origin of airborne insects and the role of aerial insectivores as agents of the biological control of crop insect pests, especially the determination of depredation rates and the cascading effects of insectivory on crop damage and yield.

Severe recent decrease of adult body mass in a declining insectivorous bird population.

Migratory bird species that feed on air-borne insects are experiencing widespread regional declines, but these remain poorly understood. Agricultural intensification in the breeding range is often regarded as one of the main drivers of these declines. Here, we tested the hypothesis that body mass in breeding individuals should reflect habitat quality in an aerial insectivore, the tree swallow (Tachycineta bicolor), along a gradient of agricultural intensity. Our dataset was collected over 7 years (2005-2011) and included 2918 swallow captures and 1483 broods. Analyses revealed a substantial decline of the population over the course of the study (-19% occupancy rate), mirrored by decreasing body mass. This trend was especially severe in females, representing a total loss of 8% of their mass. Reproductive success was negatively influenced by intensive agriculture, but did not decrease over time. Interestingly, variation in body mass was independent of breeding habitat quality, leading us to suggest that this decline in body mass may result from carry-over effects from non-breeding areas and affect population dynamics through reduced survival. This work contributes to the growing body of evidence suggesting that declines in migratory aerial insectivores are driven by multiple, complex factors requiring better knowledge of year-round habitat use.

Seasonal Shift in the Diet Composition of European Bee-EatersMerops apiasterat the Northern Edge of Distribution

Summary. European bee-eaters Merops apiaster forage almost exclusively on airborne insects caught on the wing. The availability of this food might be temporally limited due to adverse weather conditions, especially at climatically sub-optimal breeding sites. We determined seasonal variation in the diet composition in adult and nestling bee-eaters at the species' northernmost breeding colonies by analysing food remains from pellets and by direct observation. Adult bee-eaters preyed on a wide range of insect species with more than 97% belonging to the taxonomic orders Hymenoptera, Odonata and Coleoptera. We observed consistent seasonal changes in adult diet composition from the pre-incubation to the late chick rearing period. The dry mass proportion of dragonflies decreased remarkably in the adult diet as chick rearing started, whereas the consumption of small Hymenopterans increased by the end of the chick provisioning period. Additionally, we found differences in the diet composition of adults and nestlin...

A whispering bat that screams: bimodal switch of foraging guild from gleaning to aerial hawking in the desert long-eared bat.

Echolocating bats have historically been classified as either loud aerial hawkers or whispering gleaners. Some bat species can forage in multiple ways and others have demonstrated limited flexibility in the amplitude of their echolocation calls. The desert long-eared bat, Otonycteris hemprichii, has been said to be a passive gleaning whispering bat preying on terrestrial arthropods such as scorpions. Using an acoustic tracking system, we recorded individuals flying at foraging and drinking sites and compared their flight height, flight speed, call duration, pulse interval and source levels with those of gleaning individuals previously recorded using the same setup. We found differences in all variables with the strongest difference in source levels, where bats called at a mean of 119 dB peSPL (compared with 75 dB peSPL when gleaning). Bat faecal analysis indicated that their diet differed from previous studies and that prey species were capable of flight. We conclude that the bats switched from passive gleaning to capturing airborne insects (aerial hawking). Although whispering bats have been known to opportunistically catch insects on the wing, in the present study we show a full bimodal switch between foraging guilds with the respective changes in source level to those typical of a true aerial hawker.

The aerial invertebrate fauna of subantarctic Macquarie Island

Aim The extent and diversity of invertebrate aerial dispersal both on remote islands and in polar regions has long been of interest to biogeographers. We therefore monitored the airborne dispersal of insects and other micro- and macroinvertebrates to and on Macquarie Island in order to assess (1) the magnitude and composition of local aerial dispersal activity by the island's invertebrate fauna, and (2) the potential for exotic arrival and establishment. Location Macquarie Island. Methods Two robust wind-traps were run year-round on Macquarie Island from 1991 to 1994 to collect airborne insects and other micro- and macroinvertebrates. Results More than 3000 invertebrates were caught in these traps over the sampling period in the most comprehensive aerial survey of subantarctic invertebrates to date. Representatives of seven orders of Insecta were captured: Psocoptera, Thysanoptera, Hemiptera, Coleoptera, Diptera, Lepidoptera and Hymenoptera. Other taxa captured included other arthropods (Arachnida and Collembola) but also terrestrial Gastropoda. Evidence of possible long-distance dispersal (LDD) was limited to two exotic catches (one species of Collembolon, and one species of Thysanoptera). The abundance and composition of indigenous invertebrates caught in the traps indicates that the frequency of short-distance dispersal (SDD) movements on the island far exceeds that which had previously been realized. Main conclusions More than half the total catch (53%) was of flightless (i.e. passively dispersed) invertebrates, with 84% of them flightless in one of the two traps. The extent of passive dispersal movements is consistent, with most invertebrates being widely distributed at a whole-island scale. Aerial dispersal may act as a conduit for non-indigenous arrivals but this occurs infrequently. Other explanations for exotic species in traps are equally likely. The implications of these findings are discussed in relation to terrestrial invertebrate biogeography.