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The Bearing Capacity and the Rational Loading Mode of Pigeon during Takeoff



A bio-robot treats the living animal itself as the robot-moving carrier, which possesses good mobility and adaptability even in complicated non-structured environments. As one of the flyable bio-robots, pigeon-robots have been studied for several years. However, how to arrange the equipments on board effectively to minimize the impact to pigeons natural flight has not been considered. In this study, we estimated the bearing capacity of a pigeon during takeoff by increasing the weight gradually. Different loading modes have also been compared to find a rational way to reduce the influence of the loading to flyability. These results are expected to be helpful to the design of pigeon-robots.
The Bearing Capacity and the Rational Loading Mode of Pigeon during
Tingting LIU1,2,a, Lei CAI1, Hao WANG*,1,b, Zhendong DAI1, Wenbo WANG1
1Institute of Bio-inspired Structure and Surface Engineering, Nanjing University of Aeronautics and
Astronautics, Nanjing 210016, china
2college of automation engineering, Nanjing University of Aeronautics And Astronautics, Nanjing
210016, china
aemail:, bemail:
*corresponding author: Hao WANG
Keywords: pigeon-robot; bearing capacity; loading mode; pigeon (Columba livia)
A bio-robot treats the living animal itself as the robot-moving carrier, which possesses good
mobility and adaptability even in complicated non-structured environments. One of the flyable
bio-robotspigeon-robotshave been studied for several years. However, the arrangement of
equipment on board effectively to minimize the impact on pigeons’ natural flight has not been
considered. In this study, we estimated the bearing capacity of a pigeon during takeoff by increasing
the weight gradually. Different loading modes have also been compared to find a rational way to
reduce the influence of the loading to flyability. The results are expected to be helpful to design
As a common bird in our daily lives, pigeon’s good orientation discrimination, enduring flight
and load carrying flyability have impressed many scholars. The pigeon-robot [1] has a high practical
value both in military and civilian application. For example, it can be used in the tasks of
investigation, radar interference, the wild tracing and resources exploration. To successfully
perform these tasks, pigeon would be equipped with some special devices [2-4], which propose a
very high demand on the load-bearing capacity of pigeon.
So far, few studies concerning animals bearing ability during flight have been conducted
specifically and systematically. Most scholars focused on the animal’s mechanical energy
consumption or some birds’ flying kinematics and aerodynamics under conditions of loading [5-9].
Animals maximum bearing capacity may involve many factors such as temperature, altitude, wind
characters and flying space. Different species of animals may have different load carrying abilities.
Patsy M. Hughes et al. [5] studied the long-eared bat’s flight performance with the addition of
artificial wing loading. With the increase in wing loading, the bat’s flying speed decreased [5]. Six
ruby-throated hummingbirds hovering performance under conditions of maximum load had been
studied by Peng Chai who described a way of measuring the maximal load-lifting capacity of
hummingbirds [6]. Robert L. Nudds et al. revealed that the costs of carrying additional mass of
finches during routine short flights were behavioral and not energetic [7]. James H. Marden showed
that the bird’s bearing capacity during flying was associated with many aspects of the animal itself
and he compared the impact on the production of the muscle mass-specific lift which was related to
Applied Mechanics and Materials Vol. 461 (2014) pp 122-127
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the bearing capacity [8]. Meanwhile the loading modes may also have some influence on the
research results. Peter G. Tickle et al. investigated the effect of load placement on the energy
consumption of barnacle goose [9]. Therefore, the arrangement of equipment on board effectively to
minimize the impact on pigeons’ natural behavior requires investigation.
In this study we measured the maximum load bearing capacity of pigeon during takeoff and
compared the effects of two different loading modes. This experiment is expected to play an
important referential role in research and design of pigeon-robots.
Materials and Methods
Animals were healthy adult pigeons (Columba livia) with average weight of 484.8±17.6 g. Five
pigeons with intact flight feathers marked 1 to 5 were served as subjects and were housed in a
dovecote. They were supplied with enough food and water and were released every day. The
experimental procedures were in accordance with the animal protection departments guidelines.
Experimental Arena and Experimental Tools
Loading trials were conducted in a cage with dimensions of 2 m×1.2 m×1.8 m (L×W×H).
Canvas with Julesz pattern was attached to the four walls of the cage in order to prevent outside
visual interference and to help pigeons to recognize and remember experimental environment. The
pigeon’s minimum resolution angle was about 25'39' [10] and the length of the cage was 2 m. The
minimum resolution distance was 0.024 cm0.029 cm and choosing 5 cm as the random grid side
length was enough for the pigeon to discriminate. Food containers and water box were placed on
another wall of the cage. A 1.4 m high habitat rod was hung near the food containers and water box.
The rod was rough enough to ensure that the pigeons could stand on it stably. A strap penetrating
from both sides of the wing bottom of the pigeon was made and a bag filled with weights (per unit
weight 5 g) was connected to the strap.
Experimental Specifications and Experimental Procedures
Certain criterions were defined for a scientific analysis. Here we defined successful takeoff as
those flights that pigeons could lift the loads to the rod within 5 min as soon as they got into the
experimental arena. The whole experimental process consisted of three stages. The first stage was
training stage including getting familiar with the environment and flying with load training. The
second stage was the maximum load measuring stage and the last stage was statistical analysis stage.
The training stage was necessary for the first trial. Let five starving pigeons be in the arena at least
one day to know the condition well. Through the pre-experimental experience we knew that pigeons
which had not been trained to fly with load seldom had the awareness of flying upward with load on
their bodies. The weight used in this stage was only 72 g. Trained pigeons would be used in the
second stage in which they need not to be starved. Here we defined the basic weight as 72 g and per
unit weight as 5 g. During the trail we got the maximum load by increasing the weight gradually
until the pigeon was not able to take off successfully. The 5 pigeons’ trials were conducted for three
rounds in turns. The pigeon with the maximum load must take off successfully at least twice in the
three round trials. Between each round a pigeon was allowed to take food for 30 s on the rod and
taken away to rest in a room without interference. When the pigeons were very familiar with the
arena, the training stage could be omitted. The last analysis stage using the software SPSS 10.0 and
GraphPad Prism V5.01 to process the result data. As to the loading mode experiment, we chose the
load placements below the xiphoid and on the back of pigeon respectively. A view of load
placement on a pigeon is given in Fig. 1.
Applied Mechanics and Materials Vol. 461 123
The pigeon was weighted before each trial. The maximum bearing capacity was described as the
ratio of the maximum load to pigeon’s weight. The loading mode experiment was not conducted on
the same day, so the body mass of a pigeon was different. As this experiment aimed at obtaining the
ratio value, the impact of different body mass for the same pigeon could be neglected. Table 1
showed the results of the two different loading modes. The maximum load below the xiphoid could
reach to about 25%27% of the body mass. The overall trend of bearing capacity was that pigeon
could lift more loads below the xiphoid than on the back.
Table 1 Outcome of the maximum load below the xiphoid and on the back. X means the mode
below xiphoid and b means the mode on the back.
weight [g]
load [g]
Fig. 2 showed the scatter plot of table 1. The mean value of maximum load below the xiphoid
was larger than that on the back. Fig. 3 showed the results of the mean value in the two loading
modes. The confidence interval of the mean was defined as 90% and we got P<0.1, which indicated
that there was a great difference between the two modes. Thus we could conclude that the bearing
capacity below the xiphoid was stronger than that on the back. The number 2 pigeon stood out the
five pigeons, so we eliminated it and got a new comparison of mean value which is shown in Fig. 3
Fig. 1. Pigeons in bearing capacity test.
Left is carrying a load in front of chest (below the xiphoid) and the right is on the back.
124 Advances in Bionic Engineering
The pigeon’s maximum bearing capacity during takeoff was about 2527% of its body mass
and with this load it could fly to a 1.4 meter high rod. The measuring way was different from what
Peng Chai described in his paper [6]. The load he used was a 76 cm long thread with added weights.
Here we only used a small bag filled with weights instead because the pigeon may trip over by a
long tread. During the experiment some tips were noted. For example, pigeons must be given freely
Fig. 2. The scatter plot in the two
loading modes. The mean value
below the xiphoid and on the
back was 25.40% and 20.09%
respectively. The blue lines
represent mean value and the red
lines represent the standard
deviation. The solid circles and
rectangles represent the five
pigeons ratio data as showed in
table 1.
Fig. 3. The results of mean value comparison using one-way ANOVA process.
A: the difference between groups with five original data, P<0.1. B: the difference between
groups with number 2 pigeon eliminated, P<0.05. Either A or B could showed that the rational
placement of loading was below the xiphoid of the pigeon body.
Applied Mechanics and Materials Vol. 461 125
flying time during the experiment period for not weakening their flying abilities or flying
willingness with long time captivity. Do not injure the wings and feathers when loading weights to
the pigeon. Pigeon should be allowed to rest after each flight for takeoff to recover energy
consumed during this process.
As to the loading mode, we only chose the back and chest (below the xiphoid), on account that
other parts such as foot and head may not bear heavy load as the two locations tested using common
sense. In the test with loading below xiphoid, bag filled with weights was hung on a little hook (Fig.
1A), so it cannot avoid swaying during takeoff. This may reduce the lifting capacity during takeoff,
but the results showed that even in this case the bearing capacity was much better than that on the
back. Therefore, we can estimate that if the bag clings to the pigeon’s chest as shown in Fig. 1B, the
differences between the bearing capacities of the two modes will be more obvious. The bearing
capacity below the xiphoid was 5.31 percent (mean value) higher than that on the back. This may be
due to the height of the center of gravity with load on the back thereby the stability during takeoff
was reduced significantly. It’s also possible that the wing beat action was slightly blocked due to the
bag’s size on the back. The area that can completely keep clear of the wings on the back was very
small, the size of the bag should be designed adequately.
The greatest hallmark that sets a pigeon-robot apart from a common mechanical robot is its
strong elusiveness. We could refer to the rational loading mode and maximum load of a pigeon
when equipping the bird with some specific devices. In future, more details about take off with load
could be recorded with a high speed camera [11-12]. This was we can learn more about the lift
production, aerodynamics, and hydromechanics during takeoff of pigeons, which may be expected
to be helpful to design of a bionic flying micro-robot.
I would like to thank my workmates Jingdan Shao for her assistance with this experiment and
Lei Shang for his help in building an experimental arena. This research was partially supported by
China Postdoctoral Science Foundation (2012T50497).
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Applied Mechanics and Materials Vol. 461 127
Advances in Bionic Engineering
The Bearing Capacity and the Rational Loading Mode of Pigeon during Takeoff
... Homing pigeons (Columba livia domestica) possess good orientation discrimination ability, long-distance flying capability, load-bearing capacity, and easy accessibility, making them an ideal model for testing the impact of tags on motor behavior. Liu et al. (2013) measured the maximum load-bearing capacity of pigeons; however, the specific tag position remains unclear. It is necessary to clarify the specific tag position, determine the relationship between the maximum load-bearing capacity and the tag position, and minimize the deleterious impact of tags. ...
... In this part of the study, we collected a small amount of data; thus, no systematic statistics and analysis were performed, and these results were for reference only. The maximum load-bearing capacity of pigeons during initial flight is reportedly 20.09% (Liu et al. 2013), which is much higher than that observed in our study (8.0%). This may be attributed to different test facilities. ...
... This may be attributed to different test facilities. Liu et al. (2013) conducted loading trials in a cage sized 2 × 1.2 × 1.8 m 3 (length × width × height); whereas, we used arena sized 0.8 × 0.8 m 2 (radius × height). It is possible that the pigeons require time to adjust from the beginning of the ascent to flying over different heights; this could be attributed to the lower load-bearing capacity observed in our study. ...
Full-text available
Tags, such as GPS tags and satellite tags, are widely used in wildlife research as a useful tool for observing behavioral ecology. Here, we investigated the impact of tag position and mass on the motor behavior of pigeons (Columba livia domestica). We used sandbags sized 4 × 4 cm2 to simulate load and assess load capacity. The results showed that the tag had the least impact on the pigeons when attached to the middle of the synsacrum: the change rate of height (CRH) was − 4.48%, the change rate of tail angle (TA) was 14.61%, the change rate of tarsometatarsal angle (TMA) was 17.90%, and the change rate of activity level (AL) was 85.96%. The tag mass ≤ 30 g (6.0% of body mass) had relatively little impact on pigeons: CRH was ≤ 7.0%, TA was ≤ 22.51%, TMA was ≤ 5.28%, and AL was ≥ 82.95%. We then tested the impact of the tag mass at its optimum location on the motor behavior of the birds. With increase in the tag mass, the step length became longer and the time of passing through the labyrinth decreased. With the tag mass of 30 g, the pigeons could easily fly out of the arena during initial flight. In conclusion, the optimal position of the tag was in the middle of the synsacrum, and the tag mass of ≤ 6.0% of the body mass had the least impact on pigeons. Thus, tag mass should be much less than 6.0% of the body mass in application for pigeons.
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Maximum lift production during takeoff in still air was determined for a wide variety of insects and a small sample of birds and bats, and was compared with variation in morphology, taxonomy and wingbeat type. Maximum lift per unit flight muscle mass was remarkably similar between taxonomic groups (54–63 N kg−1), except for animals using clap-and-fling wingbeats, where muscle mass-specific lift increased by about 25 % (72–86 N kg−1). Muscle mass-specific lift was independent of body mass, wing loading, disk loading and aspect ratio. Birds and bats yielded results indistinguishable from insects using conventional wingbeats. Interspecific differences in short-duration powered flight and takeoff ability are shown to be caused primarily by differences in flight muscle ratio, which ranges from 0.115 to 0.560 among species studied to date. These results contradict theoretical predictions that maximum mass-specific power output and lift production should decrease with increasing body mass and wing disk loading.
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Takeoff and landing are critical phases in a flight. To better understand the functional importance of the kinematic adjustments birds use to execute these flight modes, we studied the wing and body movements of pigeons (Columba livia) during short-distance free-flights between two perches. The greatest accelerations were observed during the second wingbeat of takeoff. The wings were responsible for the majority of acceleration during takeoff and landing, with the legs contributing only one-quarter of the acceleration. Parameters relating to aerodynamic power output such as downstroke amplitude, wingbeat frequency and downstroke velocity were all greatest during takeoff flight and decreased with each successive takeoff wingbeat. This pattern indicates that downstroke velocity must be greater for accelerating flight to increase the amount of air accelerated by the wings. Pigeons used multiple mechanisms to adjust thrust and drag to accelerate during takeoff and decelerate during landing. Body angle, tail angle and wing plane angles all shifted from more horizontal orientations during takeoff to near-vertical orientations during landing, thereby reducing drag during takeoff and increasing drag during landing. The stroke plane was tilted steeply downward throughout takeoff (increasing from -60+/-5 deg. to -47+/-1 deg.), supporting our hypothesis that a downward-tilted stroke plane pushes more air rearward to accelerate the bird forward. Similarly, the stroke plane tilted upward during landing (increasing from -1+/-2 deg. to 17+/-7 deg.), implying that an upward-tilted stroke plane pushes more air forward to slow the bird down. Rotations of the stroke plane, wing planes and tail were all strongly correlated with rotation of the body angle, suggesting that pigeons are able to redirect aerodynamic force and shift between flight modes through modulation of body angle alone.
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Load carrying has been used to study the energetics and mechanics of locomotion in a range of taxa. Here we investigated the energetic and kinematic effects of trunk and limb loading in walking barnacle geese (Branta leucopsis). A directly proportional relationship between increasing back-load mass and metabolic rate was established, indicating that the barnacle goose can carry back loads (up to 20% of body mass) more economically than the majority of mammals. The increased cost of supporting and propelling the body during locomotion is likely to account for a major proportion of the extra metabolic cost. Sternal loads up to 15% of body mass were approximately twice as expensive to carry as back loads. Given the key role in dorso-ventral movement of the sternum during respiration we suggest that moving this extra mass may account for the elevated metabolic rate. Loading the distal limb with 5% extra mass incurred the greatest proportional rise in metabolism, and also caused increases in stride length, swing duration and stride frequency during locomotion. The increased work required to move the loaded limb may explain the high cost of walking.
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The doubly-labeled water technique and video were used to measure the effect of mass loading on energy expenditure and takeoff performance in zebra finches, Taeniopygia guttata, that were making routine (nonalarm) short flights. Finches that carried 27% additional mass did not expend more energy during flight than unloaded controls. Carrying additional mass, however, led to a reduced body mass and a decreased velocity during takeoffs (by 12%). Calculations of instantaneous mechanical power indicated that energy expended by unloaded and loaded finches at takeoff was similar, due to the observed decrease in velocity by mass-loaded finches and a lowering of their body mass. During routine short flights, zebra finches appear to maintain their metabolic power input and mechanical power output regardless of mass loading. Here, the costs of carrying additional mass during routine short flights were revealed to be behavioral and not energetic.
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Differential pressure measurements offer a new approach for studying the aerodynamics of bird flight. Measurements from differential pressure sensors are combined to form a dynamic pressure map for eight sites along and across the wings, and for two sites across the tail, of pigeons flying between two perches. The confounding influence of acceleration on the pressure signals is shown to be small for both wings and tail. The mean differential pressure for the tail during steady, level flight was 25.6 Pa, which, given an angle of attack for the tail of 47.6 degrees , suggests the tail contributes 7.91% of the force required for weight support, and requires a muscle-mass specific power of 19.3 W kg(-1) for flight to overcome its drag at 4.46 m s(-1). Differential pressures during downstroke increase along the wing length, to 300-400 Pa during take-off and landing for distal sites. Taking the signals obtained from five sensors sited along the wing at feather bases as representative of the mean pressure for five spanwise elements at each point in time, and assuming aerodynamic forces act within the x-z plane (i.e. no forces in the direction of travel) and perpendicular to the wing during downstroke, we calculate that 74.5% of the force required to support weight was provided by the wings, and that the aerodynamic muscle-mass specific power required to flap the wings was 272.7 W kg(-1).
A series of experiments is described in which two brown long-eared bats Plecotus auritus Linnaeus (Chiroptera: Vespertilionidae) were flown in a 1 m ×1 m×4.5 m flight enclosure at a range of body masses (n=9 experiments for a female bat, and n=11 for a male bat). The highest three of these masses incorporated artificial loads. Stroboscopic stereophotogrammetry was used to make three-dimensional reconstructions (n=124) of the bats’ flight paths. Over the entire range of experiments, wing loading was increased by 44% for the female and 46% for the male bat. Effects arising from captivity were controlled for: experiments at certain wing loadings were repeated after a period in captivity and the response to load was found to be unaltered. Flight speed fell with total mass M or with wing loading, varying as M−0.49 in the female and M−0.42 in the male bat. Wingbeat frequency increased with total mass or wing loading, varying as M0.61 in the female and M0.44 in the male bat. Hence frequency, but not speed, changed with mass in the direction predicted by aerodynamic theory. These results were used in a mathematical model to predict wingbeat amplitude, flight power and cost of transport. The model was also used to estimate the optimal flight speeds Vmr and Vmp. The model predicted that amplitude increases with load. Measurements of wingbeat amplitude did not differ significantly from the predicted values. The observed flight speed was below the predicted minimum power speed Vmp (which increases with load), and diverged further from this with progressive loading. The increase in cost of flight calculated by the model over the range of wing loadings was approximately double that which it would have been had the bats adopted the optimal approach predicted by the model. The limitations inherent in the theoretical model, and the possible constraints acting on the animals, are discussed.
The pigeon's threshold for discrimination of horizontal versus vertical lines was at approximately 23 to 29 seconds. Even with the lines subtending large visual angles, however, discrimination was never highly accurate. Human subjects tested under similar conditions possessed an acuity about half that of the pigeons. "The theories of homing that ascribe good vision to pigeons seem," according to the author, "well-grounded in fact." Bibliography. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Maximal load-lifting capacities of six ruby-throated hummingbirds (Archilochus colubris) were determined under conditions of burst performance. Mechanical power output under maximal loading was then compared with maximal hovering performance in hypodense gas mixtures of normodense air and heliox. The maximal load lifted was similar at air temperatures of 5 and 25 degrees C, and averaged 80% of body mass. The duration of load-lifting was brief, of the order of 1 s, and was probably sustained via phosphagen substrates. Under maximal loading, estimates of muscle mass-specific mechanical power output assuming perfect elastic energy storage averaged 206 W kg-1, compared with 94 W kg-1 during free hovering without loading. Under conditions of limiting performance in hypodense mixtures, maximal mechanical power output was much lower (131 W kg-1, five birds) but was sustained for longer (4 s), demonstrating an inverse relationship between the magnitude and duration of maximum power output. In free hovering flight, stroke amplitude and wingbeat frequency varied in inverse proportion between 5 and 25 degrees C, suggesting thermoregulatory contributions by the flight muscles. Stroke amplitude under conditions of maximal loading reached a geometrical limit at slightly greater than 180 degrees. Previous studies of maximum performance in flying animals have estimated mechanical power output using a simplified actuator disk model without a detailed knowledge of wingbeat frequency and stroke amplitude. The present load-lifting results, together with actuator disc estimates of induced power derived from hypodense heliox experiments, are congruent with previous load-lifting studies of maximum flight performance. For ruby-throated hummingbirds, the inclusion of wingbeat frequency and stroke amplitude in a more detailed aerodynamic model of hovering yields values of mechanical power output 34% higher than previous estimates. More generally, the study of performance limits in flying animals necessitates careful specification of behavioral context as well as quantitative determination of wing and body kinematics.
Recording single cells from alert rats currently requires a cable to connect brain electrodes to the acquisition system. If no cable were necessary, a variety of interesting experiments would become possible, and the design of other experiments would be simplified. To eliminate the need for a cable we have developed a one-channel radiotelemetry system that is easily carried by a rat. This system transmits a signal that is reliable, highly accurate and can be detected over distances of > or = 20 m. The mobile part of the system has three components: (1) a headstage with built-in amplifiers that plugs into the connector for the electrode array on the rat's head; the headstage also incorporates a light-emitting diode (LED) used to track the rat's position; (2) a backpack that contains the transmitter and batteries (2 N cells); the backpack also provides additional amplification of the single cell signals; and (3) a short cable that connects the headstage to the backpack; the cable supplies power to the headstage amplifiers and the LED, and carries the physiological signals from the headstage to the backpack. By using a differential amplifier and recording between two brain microelectrodes the system can transmit action potential activity from two nearly independent sources. In a future improvement, two transmitters with different frequencies would be used telemeter signals from four microelectrodes simultaneously.