Harmonic Radar Tracking Research Articles

Lost in space and time: robust demography and enhanced resilience buffer adverse environmental effects in a highly isolated and sedentary pre-pleistocene landscape vertebrate

BackgroundFew animal populations have been studied under the framework of the OCBIL theory, which addresses the ecology and evolution of biodiversity on old climatically buffered infertile landscapes. Available genetic data challenge the low connectivity and high genetic differentiation predicted for isolated tepui-summit vertebrate communities, suggesting potential dispersal among summits. However, the OCBIL theory posits reduced dispersibility, enhanced resilience to habitat fragmentation and inbreeding due to small populations. We tested these hypotheses by conducting the first analytic evaluation of the spatial ecology and population biology of a tepui-summit vertebrate at multiple spatial scales.ResultsWe used harmonic radar tracking (100 individuals/448 points of contact) and capture-mark-recapture data (596 individuals captured/52 recaptured) to reveal the temporal niche, microhabitat use, population size, and dispersal abilities of the tepui-summit endemic toad Oreophrynella quelchii on Roraima-tepui. Abundance was determined using a closed population model incorporating sources of variation in capture probability. We tested the relative influence of biotic and abiotic variables on distances moved through model selection. Our data indicate that the population size of O. quelchii is remarkably large (ca. 12 million individuals), with strong seasonal demographic fluctuations. Ecology and observed limited spatial movements challenge the likelihood of active dispersal among tepui tops in this species. Our results are counter to those predicted by the available genetic data but support two hypotheses of the OCBIL theory: reduced dispersibility and enhanced resilience. However, they do not support the expectation of a small refugial population size.ConclusionWe postulate that the insular, hostile tepui-summit environment tends to produce robust demographic populations, likely to buffer stochastic adverse environmental effects, rather than diversity, as observed in much younger post-Pleistocene Neotropical landscapes. Our results draw attention to the value of faunal studies using an OCBIL framework to better understand the ecology and evolution of this unique biota worldwide.

Shedding light with harmonic radar: Unveiling the hidden impacts of streetlights on moth flight behavior

One of the most dramatic changes occurring on our planet is the ever-increasing extensive use of artificial light at night, which drastically altered the environment to which nocturnal animals are adapted. Such light pollution has been identified as a driver in the dramatic insect decline of the past years. One nocturnal species group experiencing marked declines are moths, which play a key role in food webs and ecosystem services such as plant pollination. Moths can be easily monitored within the illuminated area of a streetlight, where they typically exhibit disoriented behavior. Yet, little is known about their behavior beyond the illuminated area. Harmonic radar tracking enabled us to close this knowledge gap. We found a significant change in flight behavior beyond the illuminated area of a streetlight. A detailed analysis of the recorded trajectories revealed a barrier effect of streetlights on lappet moths whenever the moon was not available as a natural celestial cue. Furthermore, streetlights increased the tortuosity of flights for both hawk moths and lappet moths. Surprisingly, we had to reject our fundamental hypothesis that most individuals would fly toward a streetlight. Instead, this was true for only 4% of the tested individuals, indicating that the impact of light pollution might be more severe than assumed to date. Our results provide experimental evidence for the fragmentation of landscapes by streetlights and demonstrate that light pollution affects movement patterns of moths beyond what was previously assumed, potentially affecting their reproductive success and hampering a vital ecosystem service.

Radio Telemetry and Harmonic Radar Tracking of the Spotted Lanternfly, Lycorma delicatula (White) (Hemiptera: Fulgoridae).

Lycorma delicatula (White) (Hemiptera: Fulgoridae), spotted lanternfly (SLF), is an invasive pest that feeds and oviposits on numerous woody and herbaceous plants important to agricultural, forest, ornamental, and nursery industries. Describing and understanding SLF movements is key to implementing surveillance and control strategies for this pest and projecting population spread. We used radio telemetry (RT) and harmonic radar (HR) to track the movements of individual SLF at field sites in eastern Pennsylvania and northwestern New Jersey. SLF equipped with HR or RT tags were tracked in 2019 and 2020 from adult emergence until oviposition time, and their movements are described. Although the bulkier RT tags disproportionately affected the distance traveled by males, which are smaller than females, both males and females were more likely to be lost due to signal attenuation when affixed with the lighter-weight HR tags. Females were tracked moving longer distances than males, with maximum distances of 434 m by a single female and 57 m by a single male. A significant positive relationship was found between their height in trees and the distance of subsequent movement. Adult SLF were found in trees predominantly at heights between 6-9 m high. For the fraction of SLF found at eye level, males, but not females, significantly moved above eye level in the weeks prior to mating, likely resulting in the observed sex ratio shift that defines the Early-2 stage. During mating time, tracked SLF were significantly higher than 8 m and oriented to trees where tight aggregations of SLF were present. This orientation towards tight aggregations started when mating began and peaked in the following 2.5 weeks for males in Late-1 and the beginning of Late-2 (after oviposition began), whereas females started this orientation behavior a half-week after males, and this activity peaked for two weeks. Male and female SLF adults exhibited slight differences in host preference, and strong preferences for wild grape, black walnut, sweet birch, and tree-of-heaven were observed. The HR-tagged nymphs moved up to 27.6 m over a five-day period in a cornfield. Nitinol wire HR tags performed better than Wollaston process or tungsten wire tags. SLF movement parameters in the field are described.

Harmonic radar tracking reveals that honeybee drones navigate between multiple aerial leks

SummaryMale honeybees (drones) are thought to congregate in large numbers in particular “drone congregation areas” to mate. We used harmonic radar to record the flight paths of individual drones and found that drones favored certain locations within the landscape which were stable over two years. Drones often visit multiple potential lekking sites within a single flight and take shared flight paths between them. Flights between such sites are relatively straight and begin as early as the drone's second flight, indicating familiarity with the sites acquired during initial learning flights. Arriving at congregation areas, drones display convoluted, looping flight patterns. We found a correlation between a drone's distance from the center of each area and its acceleration toward the center, a signature of collective behavior leading to congregation in these areas. Our study reveals the behavior of individual drones as they navigate between and within multiple aerial leks.

Harmonic radar tracking reveals random dispersal pattern of bumblebee (Bombus terrestris) queens after hibernation

The dispersal of animals from their birth place has profound effects on the immediate survival and longer-term persistence of populations. Molecular studies have estimated that bumblebee colonies can be established many kilometers from their queens’ natal nest site. However, little is known about when and how queens disperse during their lifespan. One possible life stage when dispersal may occur, is directly after emerging from hibernation. Here, harmonic radar tracking of artificially over-wintered Bombus terrestris queens shows that they spend most of their time resting on the ground with intermittent very short flights (duration and distance). We corroborate these behaviors with observations of wild queen bees, which show similar prolonged resting periods between short flights, indicating that the behavior of our radar-monitored bees was not due to the attachment of transponders nor an artifact of the bees being commercially reared. Radar-monitored flights were not continuously directed away from the origin, suggesting that bees were not intentionally trying to disperse from their artificial emergence site. Flights did not loop back to the origin suggesting bees were not trying to remember or get back to the original release site. Most individuals dispersed from the range of the harmonic radar within less than two days and did not return. Flight directions were not different from a uniform distribution and flight lengths followed an exponential distribution, both suggesting random dispersal. A random walk model based on our observed data estimates a positive net dispersal from the origin over many flights, indicating a biased random dispersal, and estimates the net displacement of queens to be within the range of those estimated in genetic studies. We suggest that a distinct post-hibernation life history stage consisting mostly of rest with intermittent short flights and infrequent foraging fulfils the dual purpose of ovary development and dispersal prior to nest searching.

Potential of harmonic radar system for use on five economically important insects: Radar tag attachment on insects and its impact on flight capacity

Harmonic radar tracking system for insects has been introduced to understand insect movement, particularly those which move at low altitudes and over relatively short ranges. Although entomologists have used direct observation and mark-and-recapture techniques as tracking methods, there are drawbacks such as low recapture rates in the case of marking techniques. The objective of this study was to quantitatively examine adhesive bond strength between radar tag and insect body and to evaluate the effect of tag attachment on flight behavior and capacity of five economically important insect species, including three pest species, Riptortus pedestris (Hemiptera: Alydidae), Lycorma delicatula (Hemiptera: Fulgoridae), and Ricania sp. (Hemiptera: Ricaniidae) and two pollinators, Apis mellifera (Hymenoptera: Apidae) and Bombus terrestris (Hymenoptera: Apidae). The adhesive bond strength was substantially different among these five insect species, but the strength was sufficiently strong for operational use in harmonic radar tagging except in Ricania sp. Bond strength on B. terrestris was 817±43.65g-forces, which was the strongest among the five species tested, while that on Ricania sp. was 1.7±0.20g-forces, which was the weakest. For all insects, no significant correlation between bond strength and insect body size was observed. The radar tag attachment affected the flight behavior and capacity of five insect species in different ways. The radar tag attachment did not significantly affect the propensity of R. pedestris, L. delicatula, or B. terrestris to takeoff compared to untagged individuals. However, the takeoff propensities of A. mellifera and Ricania sp. were negatively affected by the radar tag attachment. Flight capacities of R. pedestris, A. mellifera, and B. terrestris were not affected by the tag attachment compared to untagged individuals, but the flight capacity of Ricania sp. was negatively affected by the tag attachment. The results of this study indicate that the radar technique has promising potential for R. pedestris, L. delicatula, and B. terrestris. However, this technique may have limited potential for A. mellifera and Ricania sp. because the radar tag can significantly affect their flight behavior.

Effect of Harmonic Radar Tagging onLycorma delicatula(Hemiptera: Fulgoridae) Nymphal Mobility and Survivorship

The spotted lanternfly, Lycorma delicatula (White) (Hemiptera: Fulgoridae), has recently emerged as an invasive pest in the United States, threatening the grape and tree fruit industries. The biology of L. delicatula is poorly known. This invasive pest has rapidly spread and established itself in new regions (e.g., South Korea), taking advantage of a wide range of host plants, but virtually no studies of the dispersal capacity and patterns of the species have been published. Harmonic radar tracking provides a new tool to study the dispersal of small animals such as insects in natural field settings. In this study, we discuss procedures that allow secure attachment of harmonic radar tags on the 4th instar nymphs of L. delicatula. The adhesive bond strength between the radar tag and the nymph was sufficiently great for operational use, yielding 431.10 ± 43.37 g forces (mean ± SE). Variations in L. delicatula body size of did not affect the adhesive bond strength. Neither horizontal mobility nor vertical climbing ability of L. delicatula was affected by radar tagging when compared with untagged controls. Also, there was no significant difference in the jumping ability of radar-tagged and untagged insects. Finally, radar tagging did not affect the survivorship of L. delicatula over a 3 d test period. The results of this study indicate that the harmonic radar system can be applied successfully to 4th instars of L. delicatula without changing their mobility and survivorship. This technology facilitates study of the dispersal capacity and behavior of this invasive species under natural field conditions, and this information can serve as a basis for the development of effective monitoring and management strategies.

Does Dispersal Limit Beetle Re‐colonization of Restored Fenland? A Case Study Using Direct Measurements of Dispersal and Genetic Analysis

AbstractDispersal ability is known to limit the colonization by many fenland species onto restored habitat but factors determining colonization by wetland invertebrates onto restored fenland have not been previously examined. We used mark‐release‐recapture and harmonic radar tracking coupled with genetic analysis (ISSR‐PCR, inter‐simple sequence repeat—polymerase chain reaction) to assess the population structure and colonization of a brachypterous wetland carabid (Carabus granulatus) onto restored fenland. The first two methods were used to determine the dispersal rate of C. granulatus in the absence of barriers, while the genetic analysis was used to examine whether populations were separated by either distance or the water channels and drainage ditches that intersect fenland landscapes. Mark‐release‐recapture and harmonic radar tracking indicated that the most active 6% of individuals could travel over 25 m in a day and individuals found to be traveling these distances remained atypically active throughout the season. Thus, C. granulatus can disperse at a rate great enough to colonize all areas of restored fenland in the study site within 1 year in the absence of barriers. We found no evidence of genetically distinct sub‐populations of C. granulatus showing that distance and water barriers did not limit the movement of individuals from potential source populations to the restored habitat. This research indicates that where fenland is created with nearby established fenland, colonization opportunities should not be considered a limiting factor to colonization by wetland carabids, even where waterways divide sites.

Guidance by odors in honeybee navigation

Animal navigation is guided by multiple sensory cues. Here, we ask whether and how olfactory stimuli emanating from places other than the trained feeding site redirect the flight paths of honeybees. The flight trajectories of individual bees were registered using harmonic radar tracking. Sensory cues (compass direction, distance, visual cues en route and close to the feeding site) associated with the trained flight route dominated wayfinding, but a learned odorant carried by air flow induced excursions into the wind. These redirections were largely restricted to rather small deviations from the trained route (<60°, <200m) and occurred only if the animal did not receive the trained odorant stimulus at the trained feeding site. Under certain conditions, larger excursions were observed. These findings are discussed in the context of odor guidance of honeybees over longer distances (>300m from the hive).

Scouts behave as streakers in honeybee swarms

Harmonic radar tracking was used to record the flights of scout bees during takeoff and initial flight path of two honeybee swarms. One swarm remained intact and performed a full flight to a destination beyond the range of the harmonic radar, while a second swarm disintegrated within the range of the radar and most of the bees returned to the queen. The initial stretch of the full flight is characterized by accelerating speed, whereas the disintegrating swarm flew steadily at low speed. The two scouts in the swarm displaying full flight performed characteristic flight maneuvers. They flew at high speed when traveling in the direction of their destination and slowed down or returned over short stretches at low speed. Scouts in the disintegrating swarm did not exhibit the same kind of characteristic flight performance. Our data support the streaker bee hypothesis proposing that scout bees guide the swarm by traveling at high speed in the direction of the new nest site for short stretches of flight and slowing down when reversing flight direction.

Honeybees consolidate navigation memory during sleep

Sleep is known to support memory consolidation in animals, including humans. Here we ask whether consolidation of novel navigation memory in honeybees depends on sleep. Foragers were exposed to a forced navigation task in which they learned to home more efficiently from an unexpected release site by acquiring navigational memory during the successful homing flight. This task was quantified using harmonic radar tracking and applied to bees that were equipped with a radio frequency identification device (RFID). The RFID was used to record their outbound and inbound flights and continuously monitor their behavior inside the colony, including their rest during the day and sleep at night. Bees marked with the RFID behaved normally inside and outside the hive. Bees slept longer during the night following forced navigation tasks, but foraging flights of different lengths did not lead to different rest times during the day or total sleep time during the night. Sleep deprivation before the forced navigation task did not alter learning and memory acquired during the task. However, sleep deprivation during the night after forced navigation learning reduced the probability of returning successfully to the hive from the same release site. It is concluded that consolidation of novel navigation memory is facilitated by night sleep in bees.

Vector integration and novel shortcutting in honeybee navigation

Honeybees that had been trained to visit two feeders simultaneously were released at five sites located further away from the training area. Harmonic radar tracking was used to record the complete homing flights. The bees performed multiple straight flight components (SFCs) between curved search flights. SFCs reflect vector directions between the two feeding sites and the respective vectors between the feeding sites and the hive. Direct flights back to the hive were also observed. The latter belong to a homing strategy that requires the bee to identify its location relative to the hive. We interpret these two navigation strategies as reflecting the application of a directional component of novel shortcut flights. Taken together, our findings indicate that bees apply several different directional components of vectors which are either experienced directly during flight or derived from long-distance vector integration or mapping.

Application of harmonic radar technology to monitor tree snail dispersal

Abstract. Planned conservation efforts for tree snails of the endangered genus Achatinella, endemic to the island of O'ahu, Hawai'i, will include translocations among the remaining wild and captive‐bred populations. In order to establish optimal levels of artificial migration among neighboring groups of snails within fragmented populations, efforts to determine natural dispersal rates through direct observation were initiated. Capture–mark–recapture (CMR) efforts have proved inadequate for obtaining the requisite dispersal estimates, due to low recapture probabilities. In addition, snail dispersal beyond the boundaries of a finite CMR study site was indistinguishable from mortality. In the preliminary study reported here, both the low recapture probability and dispersal detection problems of past CMR efforts were addressed by using harmonic radar tracking. This approach yielded rough dispersal estimates that were unattainable using CMR alone by providing 100% recapture rates even beyond the normal survey area boundaries. Extensive snail movements within clusters of connected trees were frequently observed after tracking for merely a few hours, although movements between unconnected trees were rare and recorded only after monthly survey intervals. Just 11 out of 40 tracked snails made between‐tree movements (average distance of 4.94±1.52 m) during the entire 7‐month study, and provided the only data utilizable for inferring gene flow in and out of subpopulations. Meteorological data loggers were deployed when tracking began to look for an association between such snail movement and weather fluctuations. The resultant data indicate that increases in both wind gusts and humidity facilitate dispersal (R2=0.77, p‐value &lt;0.001), and that passive wind dispersal alone may be responsible for many snail movements (R2=0.59, p‐value=0.0014). Despite having provided coarse estimates of short‐term dispersal and corresponding wind influences, the limitations of the radar method can be substantial.

The potential of portable harmonic radar technology for the tracking of beneficial insects

Visual observation enables a good understanding of beneficial insect behaviour within a locality, but once the rapidly dispersing beneficial insects walk or fly, they are soon lost from view. The harmonic radar tracking system developed to follow Colorado potato beetles, Leptinotarsa decemlineata (Say) in flight is proposed as a useful technique to increase the study range of beneficial insects from that of the plant to that of the landscape. These insects belong to a wide array of orders and families and many are small in size. Nevertheless, we estimated that some 15% of beneficial insects are at least similar in length to the chrysomelid beetle for which the feasibility of using a portable harmonic radar has been successfully demonstrated. As for the Colorado beetle, the pulsed radar transmitter, the tag, the antenna gain and the receiver of the portable radar system must be carefully designed to provide both a sufficient tracking range and a sufficient beam width. The construction of the tag is strongly limited by the load-carrying ability of the beneficial insect to be tracked. For the tracking of normal insect dispersal tags must, by definition, be lighter than the maximum carrying ability for extra loads and within the wing loading range of each species. It has been shown that in herbivorous insects and mosquitoes the ability to fly may be traded against the opportunity to acquire a large meal. This trade-off, which limits the ability of the insects to carry extra loads, should be less likely to occur with beneficial species that have to remain highly mobile to locate and capture prey for example. This was supported by our findings for Hippodamia convergens and Harmonia axyridis (Coccinellidae), both of which retain their ability to fly over the full range of their wing loading values. Tests conducted in the laboratory showed that these two beneficial insects can display normal flight behaviour with tags representing a similar percentage of their body mass as those successfully developed for the Colorado beetle and only slightly higher than for the other ones reported in the literature. The application of the portable harmonic radar technology to the study of flight by beneficial insects is therefore feasible and worth developing further. The main challenge is in the development of electronic tags with a sufficiently small absolute mass. Many options available immediately and others with potential are discussed.