Wingbeat Pattern Research Articles

The physics of flight: II. Flapping wings

In any conventional aircraft the wings provide the lift and the engines provide the thrust.In a bird, however, the wings have to provide the thrust as well as the lift. In this article weshall use the ideas presented in the first article of this series to develop a simple theory toexplain how this comes about, and use it to predict some important characteristics of theflight of birds, including their wingbeat patterns and their minimum power requirements.

Radar data on wing-beat frequencies and flight speeds of two bat species

ABSTRACT This paper presents for the first time radar recorded flight paths and wing-beat pattern of two identified Palaearctic bat species. Simultaneous film recordings confirm the wing-beat pattern reflected by echo signatures. Our results suggest that discrimination of bats and nocturnally migrating birds is usually possible because the recorded bats differed from the regular flapping and pausing phases in passerines' bounding flight as well as from the regular continuous wing-beats of other nocturnal migrants (e.g., waders and waterfowl) by very short and irregularly distributed glides (flap-gliding). Small, medium and large bats may be differentiated according to wing-beat frequency. For the discrimination of the similarly sized Nyctalus noctula and Eptesicus serotinus (both with mean frequencies of 7–7.5 Hz and variation mainly between 6 and 8 Hz) ecological or behavioural features must be included. The lowest rates of flapping (even below 5 flaps per second) occurred because some flaps were prolong...

Gliding behaviour elicited by lateral looming stimuli in flying locusts

We challenged tethered, flying locusts with visual stimuli looming from the side towards one eye in a way that mimics the approach of a predatory bird. Locusts respond to the lateral approach of a looming object with steering movements and a stereotyped, rapid behaviour in which the wingbeat pattern ceases and the wings are swept into a gliding posture. This gliding behaviour may cause the locust to dive. The gliding posture is maintained for 200 ms or more after which flight is resumed with an increased wingbeat frequency or else the wings are folded. A glide begins with a strong burst of activity in the mesothoracic second tergosternal motor neuron (no. 84) on both sides of the locust. Recordings of descending contralateral movement detector (DCMD) activity in a flying locust show that it responds to small (80-mm diameter) looming stimuli during tethered flight, with a prolonged burst of spikes that tracks stimulus approach and reaches peak instantaneous frequencies as, or after, stimulus motion ceases. There is a close match between the visual stimuli that elicit a gliding behaviour and those that are effective at exciting the DCMD neuron. Wing elevation into the gliding posture occurs during a maintained burst of high frequency DCMD spikes.

Mechanization and Control Concepts for Biologically Inspired Micro Air Vehicles

It is possible that micro air vehicle (MAV) designs of the future will exploit flapping flight to perform missions that require extreme agility, such as rapid flight beneath a forest canopy or within the confines of a building. Many of nature's most agile fliers generate flapping motions through resonant excitation of an aeroelastically tailored structure: muscle tissue is used to excite a vibratory mode of their flexible wing structure that creates propulsion and lift. A number of micro air vehicle concepts have been proposed that would operate in a similar fashion. An ongoing research activity is described in which mechanization and control concepts with application to resonant flapping MAVs are being explored. Structural approaches, mechanical design, sensing, and wingbeat control concepts inspired by hummingbirds, bats, and insects are examined. Experimental results from a testbed capable of generating vibratory wingbeat patterns that approximately match those exhibited by hummingbirds in hover, cruise, and reverse flight are presented

Neural ensemble coding of target identity in echolocating bats.

Most insectivorous bats use echolocation to determine the identity of flying insects. Among the many target features that are so extracted, the insect's wingbeat pattern and frequency appear to serve as useful cues for identification. Biosonar pulses impinging on the fluttering wings of an insect are returned as echoes whose amplitudes vary with time, thus providing a characteristic signature of the insect. It has been shown previously that neurons in the inferior colliculus, a midbrain auditory nucleus, of the little brown bat respond to sound stimuli that mimic echoes from fluttering targets. To examine the manner in which target identity is represented in the inferior colliculus, an ensemble coding analysis using a filter-based approach was undertaken. The analysis indicates that a discrete subset of neurons in the inferior colliculus, the onset units, are strongly tuned to wingbeat frequencies of targets that the bat hunts, and that ensemble response reaches a maximum at a distinct phase of the prey capture maneuver: the late approach stage. On the basis of the analysis it is hypothesized that inferior colliculus neurons may play an important role in target detection-identification processing. Although ensemble coding of temporally sequenced information has not been analyzed in the auditory system so far, this study indicates that this method of coding may provide the information necessary to detect and identify targets during prey capture.

SHORT-RANGE HIGH-PRECISION SURVEILLANCE OF NOCTURNAL MIGRATION AND TRACKING OF SINGLE TARGETS

ABSTRACT Possibilities and limitations in the application of different radar types for ornithological research are summarized. Methodological details are given for the tracking radar “Superfledermaus. The pencil-beam of this radar can either be fixed at a certain angle or used in a conical or vertical scanning mode to obtain data on the spatial distribution of birds. Procedures and problems of calculating bird numbers from the radar data obtained by conical scanning are emphasized. In the tracking mode, the flight paths of single targets like birds or meteorological balloons can be recorded. The fluctuations of the radar signals provide information on the birds' wingbeat pattern, thus offering the possibility to obtain data on the proportions of different bird classes aloft and to compare the flight path data of a bird, such as track, heading, ground speed, air speed, vertical speed, gliding angle, and altitude, with wing flapping and environmental conditions.

Flight speeds observed with radar, a correction: slow ?birds? are insects

Based upon new data and re-analysis of previous data, some results concerning migration of “birds” at night are now attributed to insects. In particular, slowly flying radar targets over land (Larkin and Thompson 1980) and, by analogy, over the ocean (Larkin et al. 1979) are shown to lack wing beat patterns of birds and the appearance of birds when viewed with a radar-controlled high-power telescope and spotlamp. The insect targets overlap with birds in the amount of radar echo returned, are abundant in warmer months, and fly even in March and November in temperate North America. Other previous results are largely substantiated; however, a previous report (Larkin 1980) that migrating birds can detect the wind direction over the ocean is not substantiated.

Natural ultrasonic echoes from wing beating insects are encoded by collicular neurons in the CF-FM bat,Rhinolophus ferrumequinum

1. Acoustic reflections from a wing beating moth to an 80 kHz ultrasonic signal were recorded from six different incident angles and analyzed in spectral and time domains. The recorded echoes as well as independent components of amplitude and frequency modulations of the echoes were employed as acoustic stimuli during single unit studies. 2. The responses of single inferior colliculus neurons to these stimuli were recorded from four horseshoe bats,Rhinolophus ferrumequinum, a species which uses a long constant frequency (CF) sound with a final frequency modulated (FM) sweep during echolocation. All neurons responding to wing beat echoes reliably encoded the fundamental wing beat frequency as well as the more refined frequency and amplitude modulations. 3. These neurons may provide the bat a neural mechanism to detect periodically moving targets against a cluttered background and also to discriminate various insect species on the basis of their wing beat patterns.