Positional entropy during pigeon homing I: application of Bayesian latent state modelling

In these two companion papers, we introduce a new approach to the analysis of bird navigation which brings together several novel mathematical and technical applications. Miniaturized GPS logging devices provide track data of sufficiently high spatial and temporal resolution that considerable variation in flight behaviour can be observed remotely from the form of the track alone. We analyse a fundamental measure of bird flight track complexity, spatio-temporal entropy, and explore its state-like structure using a probabilistic hidden Markov model. The emergence of a robust three-state structure proves that the technique has analytical power, since this structure was not obvious in the tracks alone. We propose the hypothesis that positional entropy is indicative of underlying navigational uncertainty, and that familiar area navigation may break down into three states of navigational confidence. By interpreting the relationship between these putative states and features on the map, we are able to propose a number of hypothetical navigational strategies feeding into these states. The first of these two papers details the novel technical developments associated with this work and the second paper contains a navigational interpretation of the results particularly with respect to visual features of the landscape.     

Simulating geomagnetic bird navigation using novel high-resolution geomagnetic data

Birds rely on precise navigational mechanisms, especially for long-distance migrations. One debated mechanism is their use of the geomagnetic field. It is unclear if and how different species of birds are using intensity or inclination (or both) for navigation. Previous geomagnetic modelling research is based on static geomagnetic data despite a temporally and spatially varying geomagnetic field. Animals supposedly have a high sensitivity to those changes of the geomagnetic field. In order to understand how birds respond in real-time to its temporal variation, we need to use accurate geomagnetic information linked to the position of the bird through co-location in space and time.We developed a data-driven approach to simulate geomagnetic migratory strategies, using, for the first time, accurate contemporaneous geomagnetic data obtained from Swarm satellites of the European Space Agency. We created biased correlated random walk models which were based on both GPS data from greater white-fronted geese (Anser albifrons) during fall migration between north-west Russia and central Europe and contemporaneous satellite geomagnetic data. Different strategies of geomagnetic navigation associated with different geomagnetic values were translated into probability surfaces, built from geomagnetic data, and included into the random walk models. To evaluate which strategy was most likely, we compared the measured GPS trajectories to the simulated trajectories using different trajectory similarity measurements. We propose this as an approach to track many bird species for future comparative studies.We found that navigational strategies in these geese using magnetic intensity were closer to the observed data than those using inclination. This was the case in 80% of the best models and is an indication that it should be more beneficial for these geese to use intensity over inclination. Additionally, our results supported results from a previous study, that navigation based on taxis and compass mechanisms were more similar to the observed data than other mechanisms. We therefore suggest that these geese may use a combination of these strategies for navigation at a broad-scale. Overall, it seems likely that for successful navigation to the target location more than one mechanism is necessary; indicating a multifactorial navigation mechanism of these migratory geese in the study area. The satellite geomagnetic data are available at a higher temporal resolution and the use significantly improved the fit of the modelled simulations in comparison to the modelled geomagnetic data. Therefore, using annotated geomagnetic data could greatly improve the modelling of animal geomagnetic navigation in future research.     

Juvenile Osprey Navigation during Trans-Oceanic Migration

To compensate for drift, an animal migrating through air or sea must be able to navigate. Although some species of bird, fish, insect, mammal, and reptile are capable of drift compensation, our understanding of the spatial reference frame, and associated coordinate space, in which these navigational behaviors occur remains limited. Using high resolution satellite-monitored GPS track data, we show that juvenile ospreys (Pandion haliaetus) are capable of non-stop constant course movements over open ocean spanning distances in excess of 1500 km despite the perturbing effects of winds and the lack of obvious landmarks. These results are best explained by extreme navigational precision in an exogenous spatio-temporal reference frame, such as positional orientation relative to Earth''s magnetic field and pacing relative to an exogenous mechanism of keeping time. Given the age (<1 year-old) of these birds and knowledge of their hatching site locations, we were able to transform Enhanced Magnetic Model coordinate locations such that the origin of the magnetic coordinate space corresponded with each bird''s nest. Our analyses show that trans-oceanic juvenile osprey movements are consistent with bicoordinate positional orientation in transformed magnetic coordinate or geographic space. Through integration of movement and meteorological data, we propose a new theoretical framework, chord and clock navigation, capable of explaining the precise spatial orientation and temporal pacing performed by juvenile ospreys during their long-distance migrations over open ocean.     

Robotic Etiquette:Socially Acceptable Navigation of Service Robots with Human Motion Pattern Learning and Prediction

##正## Nonverbal and noncontact behaviors play a significant role in allowing service robots to structure their interactions withhumans.In this paper, a novel human-mimic mechanism of robot's navigational skills was proposed for developing sociallyacceptable robotic etiquette.Based on the sociological and physiological concerns of interpersonal interactions in movement,several criteria in navigation were represented by constraints and incorporated into a unified probabilistic cost grid for safemotion planning and control, followed by an emphasis on the prediction of the human's movement for adjusting the robot'spre-collision navigational strategy.The human motion prediction utilizes a clustering-based algorithm for modeling humans'indoor motion patterns as well as the combination of the long-term and short-term tendency prediction that takes into accountthe uncertainties of both velocity and heading direction.Both simulation and real-world experiments verified the effectivenessand reliability of the method to ensure human's safety and comfort in navigation.A statistical user trials study was also given tovalidate the users'favorable views of the human-friendly navigational behavior.     

The gliding speed of migrating birds: slow and safe or fast and risky?

Aerodynamic theory postulates that gliding airspeed, a major flight performance component for soaring avian migrants, scales with bird size and wing morphology. We tested this prediction, and the role of gliding altitude and soaring conditions, using atmospheric simulations and radar tracks of 1346 birds from 12 species. Gliding airspeed did not scale with bird size and wing morphology, and unexpectedly converged to a narrow range. To explain this discrepancy, we propose that soaring‐gliding birds adjust their gliding airspeed according to the risk of grounding or switching to costly flapping flight. Introducing the Risk Aversion Flight Index (RAFI, the ratio of actual to theoretical risk‐averse gliding airspeed), we found that inter‐ and intraspecific variation in RAFI positively correlated with wing loading, and negatively correlated with convective thermal conditions and gliding altitude, respectively. We propose that risk‐sensitive behaviour modulates the evolution (morphology) and ecology (response to environmental conditions) of bird soaring flight.     

Independence of landmark and self-motion-guided navigation: a different role for grid cells

Recent interest in the neural bases of spatial navigation stems from the discovery of neuronal populations with strong, specific spatial signals. The regular firing field arrays of medial entorhinal grid cells suggest that they may provide place cells with distance information extracted from the animal''s self-motion, a notion we critically review by citing new contrary evidence. Next, we question the idea that grid cells provide a rigid distance metric. We also discuss evidence that normal navigation is possible using only landmarks, without self-motion signals. We then propose a model that supposes that information flow in the navigational system changes between light and dark conditions. We assume that the true map-like representation is hippocampal and argue that grid cells have a crucial navigational role only in the dark. In this view, their activity in the light is predominantly shaped by landmarks rather than self-motion information, and so follows place cell activity; in the dark, their activity is determined by self-motion cues and controls place cell activity. A corollary is that place cell activity in the light depends on non-grid cells in ventral medial entorhinal cortex. We conclude that analysing navigational system changes between landmark and no-landmark conditions will reveal key functional properties.     

An edge-detection approach to investigating pigeon navigation

This study brings together work in pattern recognition and animal behaviour. By applying algorithms in pattern recognition, we examined how visual landscape information influences pigeons' homing behaviour. We used an automated procedure (Canny edge detector) to extract edges from an aerial image of the experimental terrain. Analysis of pigeons' homing routes recorded using global positioning system (GPS) trackers showed that the chosen homing paths, as well as changes in the birds' navigational states, tended to coincide with these edges. This study demonstrates that some edge-containing land features attract homing pigeons and trigger changes in their navigational states.     

Evidence for the honeybee's place knowledge in the vicinity of the hive

Upon leaving the nest for the first time, honeybees employ a tripartite orientation/exploration system to gain the requisite knowledge to return to their hive after foraging. Focal exploration comes first- the departing bee turns around to face the return target and oscillates in a lateral flight pattern of increasing amplitude and distance. Thereafter, for the peripheral exploration, the forward flying bee circles the return-goal area with expanding and alternating clockwise and counterclockwise arcs. After this two- part proximal exploration follows distal exploration, the bee flies straight towards her potential distal goal. For the return path, supported by the preceding exploratory learning, the return navigational performance is expected to reflect the three exploratory parts in reverse order. Previously only two performance parts have been experimentally identified: focal navigation and distal navigation. Here we discovered peripheral navigation as being distinct from focal and distal navigation. Like focal navigation, yet unlike distal navigation, peripheral navigation is invariably triggered by local place recognition. Whereas focal navigation (orientation) is close to unidirectional, peripheral navigation makes use of multiple goal-vector knowledge. We term the area in question the Peripheral Correction Area because within it peripheral navigation is triggered, which in turn is capable of correcting errors that accumulated during a preceding distal dead-reckoning based flight.     

Hypatia-trackRadar: A software for animal tracking using marine surveillance radars

Hypatia-trackRadar is a Java standalone application designed to help biologists extract and process bird movement data from marine surveillance radars. This application integrates simultaneous collection of radar data and field observations by allowing the user to link information gathered from visual observers (such as bird species and flock size) to the radar echoes. A virtual transparent sheet positioned on the radar screen allows the user to visually follow and track the echoes on the radar screen. The application translates the position of the echoes on the screen in a metric coordinate system. Based on time and spatial position of the echoes the software automatically calculates multiple flight parameters, such as ground speed, track length and duration. We validated Hypatia-trackRadar using an unmanned aerial vehicle. Here we present the features of this application software and its first use in a real case study in a raptor migration bottle-neck.     

Group decisions and individual differences: route fidelity predicts flight leadership in homing pigeons (Columba livia)

How social-living animals make collective decisions is currently the subject of intense scientific interest, with increasing focus on the role of individual variation within the group. Previously, we demonstrated that during paired flight in homing pigeons, a fully transitive leadership hierarchy emerges as birds are forced to choose between their own and their partner''s habitual routes. This stable hierarchy suggests a role for individual differences mediating leadership decisions within homing pigeon pairs. What these differences are, however, has remained elusive. Using novel quantitative techniques to analyse habitual route structure, we show here that leadership can be predicted from prior route-following fidelity. Birds that are more faithful to their own route when homing alone are more likely to emerge as leaders when homing socially. We discuss how this fidelity may relate to the leadership phenomenon, and propose that leadership may emerge from the interplay between individual route confidence and the dynamics of paired flight.     

Migration by soaring or flapping: numerical atmospheric simulations reveal that turbulence kinetic energy dictates bee-eater flight mode

Aerial migrants commonly face atmospheric dynamics that may affect their movement and behaviour. Specifically, bird flight mode has been suggested to depend on convective updraught availability and tailwind assistance. However, this has not been tested thus far since both bird tracks and meteorological conditions are difficult to measure in detail throughout extended migratory flyways. Here, we applied, to our knowledge, the first comprehensive numerical atmospheric simulations by mean of the Regional Atmospheric Modeling System (RAMS) to study how meteorological processes affect the flight behaviour of migrating birds. We followed European bee-eaters (Merops apiaster) over southern Israel using radio telemetry and contrasted bird flight mode (flapping, soaring-gliding or mixed flight) against explanatory meteorological variables estimated by RAMS simulations at a spatial grid resolution of 250 × 250 m(2). We found that temperature and especially turbulence kinetic energy (TKE) determine bee-eater flight mode, whereas, unexpectedly, no effect of tailwind assistance was found. TKE during soaring-gliding was significantly higher and distinct from TKE during flapping. We propose that applying detailed atmospheric simulations over extended migratory flyways can elucidate the highly dynamic behaviour of air-borne organisms, help predict the abundance and distribution of migrating birds, and aid in mitigating hazardous implications of bird migration.     

Navigation without vision: bumblebee orientation in complete darkness

In flight cages, worker bumblebees (Bombus impatiens) spontaneously explored the surroundings of their nest and foraged in complete darkness, by walking instead of flying, from feeders up to 150 cm away from the nest. This behaviour was wholly unexpected in these classically visual foragers. The finding provides a controlled system for dissecting possible non-visual components of navigation used in daylight. It also allows us to isolate navigation mechanisms used in naturally dark situations, such as in the nest. Using infrared video, we mapped walking trails. We found that bumblebees laid odour marks. When such odour cues were eliminated, bees maintained correct directionality, suggesting a magnetic compass. They were also able to assess travel distance correctly, using an internal, non-visual, measure of path length. Path integration was not employed. Presumably, this complex navigational skill requires visual input in bees.     

A Novel Augmented Reality Navigation System for Endoscopic Sinus and Skull Base Surgery: A Feasibility Study

Objective

To verify the reliability and clinical feasibility of a self-developed navigation system based on an augmented reality technique for endoscopic sinus and skull base surgery.

Materials and Methods

In this study we performed a head phantom and cadaver experiment to determine the display effect and accuracy of our navigational system. We compared cadaver head-based simulated operations, the target registration error, operation time, and National Aeronautics and Space Administration Task Load Index scores of our navigation system to conventional navigation systems.

Results

The navigation system developed in this study has a novel display mode capable of fusing endoscopic images to three-dimensional (3-D) virtual images. In the cadaver head experiment, the target registration error was 1.28 ± 0.45 mm, which met the accepted standards of a navigation system used for nasal endoscopic surgery. Compared with conventional navigation systems, the new system was more effective in terms of operation time and the mental workload of surgeons, which is especially important for less experienced surgeons.

Conclusion

The self-developed augmented reality navigation system for endoscopic sinus and skull base surgery appears to have advantages that outweigh those of conventional navigation systems. We conclude that this navigational system will provide rhinologists with more intuitive and more detailed imaging information, thus reducing the judgment time and mental workload of surgeons when performing complex sinus and skull base surgeries. Ultimately, this new navigational system has potential to increase the quality of surgeries. In addition, the augmented reality navigational system could be of interest to junior doctors being trained in endoscopic techniques because it could speed up their learning. However, it should be noted that the navigation system serves as an adjunct to a surgeon’s skills and knowledge, not as a substitute.     

Wind estimation based on thermal soaring of birds

The flight performance of birds is strongly affected by the dynamic state of the atmosphere at the birds' locations. Studies of flight and its impact on the movement ecology of birds must consider the wind to help us understand aerodynamics and bird flight strategies. Here, we introduce a systematic approach to evaluate wind speed and direction from the high‐frequency GPS recordings from bird‐borne tags during thermalling flight. Our method assumes that a fixed horizontal mean wind speed during a short (18 seconds, 19 GPS fixes) flight segment with a constant turn angle along a closed loop, characteristic of thermalling flight, will generate a fixed drift for each consequent location. We use a maximum‐likelihood approach to estimate that drift and to determine the wind and airspeeds at the birds' flight locations. We also provide error estimates for these GPS‐derived wind speed estimates. We validate our approach by comparing its wind estimates with the mid‐resolution weather reanalysis data from ECMWF, and by examining independent wind estimates from pairs of birds in a large dataset of GPS‐tagged migrating storks that were flying in close proximity. Our approach provides accurate and unbiased observations of wind speed and additional detailed information on vertical winds and uplift structure. These precise measurements are otherwise rare and hard to obtain and will broaden our understanding of atmospheric conditions, flight aerodynamics, and bird flight strategies. With an increasing number of GPS‐tracked animals, we may soon be able to use birds to inform us about the atmosphere they are flying through and thus improve future ecological and environmental studies.     

A systems interpretation for observations of bird V-formations

Birds in V formations are frequently observed and two main hypotheses have emerged to explain this particular geometry: (i) it offers aerodynamic advantages and (ii) it is used to improve visual communication. Both explanations require a bird to track its predecessor. However, most V-formations observed in nature are small and the distribution of wing-tip spacings has a large variation. This suggests that tracking the lateral position of the preceding bird is a difficult task. Control theorists, when trying to control platoons of vehicles, also noted that predecessor following is difficult. In this paper, we apply a result from systems theory to explain the observations of bird V-formations. The strength of this result is that it does not rely on the details of the bird flight model. Thus we claim that formation flight is inherently difficult for birds.     

Simulated visual homing in desert ant natural environments: efficiency of skyline cues

Desert ants, foraging in cluttered semiarid environments, are thought to be visually guided along individual, habitual routes. While other navigational mechanisms (e.g. path integration) are well studied, the question of how ants extract reliable visual features from a complex visual scene is still largely open. This paper explores the assumption that the upper outline of ground objects formed against the sky, i.e. the skyline, provides sufficient information for visual navigation. We constructed a virtual model of the ant’s environment. In the virtual environment, panoramic images were recorded and adapted to the resolution of the desert ant’s complex eye. From these images either a skyline code or a pixel-based intensity code were extracted. Further, two homing algorithms were implemented, a modified version of the average landmark vector (ALV) model (Lambrinos et al. Robot Auton Syst 30:39–64, 2000) and a gradient ascent method. Results show less spatial aliasing for skyline coding and best homing performance for ALV homing based on skyline codes. This supports the assumption of skyline coding in visual homing of desert ants and allows novel approaches to technical outdoor navigation.     

Spatial inference without a cognitive map: the role of higher-order path integration

The cognitive map has been taken as the standard model for how agents infer the most efficient route to a goal location. Alternatively, path integration – maintaining a homing vector during navigation – constitutes a primitive and presumably less-flexible strategy than cognitive mapping because path integration relies primarily on vestibular stimuli and pace counting. The historical debate as to whether complex spatial navigation is ruled by associative learning or cognitive map mechanisms has been challenged by experimental difficulties in successfully neutralizing path integration. To our knowledge, there are only three studies that have succeeded in resolving this issue, all showing clear evidence of novel route taking, a behaviour outside the scope of traditional associative learning accounts. Nevertheless, there is no mechanistic explanation as to how animals perform novel route taking. We propose here a new model of spatial learning that combines path integration with higher-order associative learning, and demonstrate how it can account for novel route taking without a cognitive map, thus resolving this long-standing debate. We show how our higher-order path integration (HOPI) model can explain spatial inferences, such as novel detours and shortcuts. Our analysis suggests that a phylogenetically ancient, vector-based navigational strategy utilizing associative processes is powerful enough to support complex spatial inferences.     

The problem of estimating wind drift in migrating birds

Whether migrating birds compensate for wind drift or not is a fundamental question in bird migration research. The procedures to demonstrate and quantitatively estimate wind drift or compensation are fraught with difficulties and pitfalls. In this paper, we evaluate four methods that have been used in several studies over the past decades. We evaluate the methods by analysing a model migratory movement with a realistic scatter in flight directions, for the ideal cases of full drift and complete compensation. Results obtained with the different methods are then compared with the "true behaviour" of the model movement, illustrating that spurious patterns of drift and compensation arise in some cases. We also illustrate and evaluate the different methods of estimating drift for a real case, based on tracking radar measurements of bird migration in relation to winds. Calculating the linear regression of mean geographic track (resulting flight direction) and heading directions (directions of the birds' body axis) of a migratory movement under different wind conditions in relation to the angle alpha (the angle between mean track and heading) always provides robust and reliable results. Comparing mean flight directions between occasions with winds from the left and right of the mean flight direction of the whole migratory movement also always provides expected and correct measures of drift. In contrast, regressions of individual flight directions in relation to alpha (the angle between track and heading for the specific individuals or flocks) are liable to produce biased and spurious results, overestimating compensation/overcompensation if following winds dominate in the analysis and overestimating drift/overdrift if opposed winds are dominating. Comparing mean directions for cases with winds from the left and right in relation to individual flight directions also gives biased and spurious results unless there is full variation in wind directions or an equal distribution of crosswinds from left and right. The results of the methodological evaluation and the analysis of the real case indicate that some earlier analyses of wind drift may have to be re-evaluated.     

Shearwaters sometimes take long homing detours when denied natural outward journey information

The cognitive processes (learning and processing of information) underpinning the long-distance navigation of birds are poorly understood. Here, we used the homing motivation of the Manx shearwater to investigate navigational decision making in a wild bird by displacing them 294 km to the far side of a large island (the island of Ireland). Since shearwaters are reluctant to fly over land, the island blocked the direct route home, forcing a navigational decision. Further still, on the far side of the obstacle, we chose a release site where the use of local knowledge could facilitate a 20% improvement in route efficiency if shearwaters were able to anticipate and avoid a large inlet giving the appearance of open water in the home direction. We found that no shearwater took the most efficient initial route home, but instead oriented in the home direction (even once the obstacle became visible). Upon reaching the obstacle, four shearwaters subsequently circumnavigated the land mass via the long route, travelling a further 900 km as a result. Hence, despite readily orienting homewards immediately after displacement, shearwaters seem unaware of the scale of the obstacle formed by a large land mass despite this being a prominent feature of their regular foraging environment.