Limits to sustainable avian flight performance

Lead Research Organisation: Bangor University
Department Name: Sch of Biological Sciences

Abstract

We propose to undertake the first detailed scientific studies into the flight biology, migratory physiology and energetics of bar-headed geese in the wild using the latest electronic dataloggering technology. Ultimately, we will address the question of where are the limits to sustainable avian flight performance at high altitudes and what is the effect of body mass? In particular, how do larger species cope during flight with the combined effects of reduced air density, low oxygen availability and decreased temperature? Only a few species of larger birds are thought to be able to sustain long periods of flapping flight at high altitudes and these have received little study. The best known species is the bar-headed goose (Anser indicus) which performs one of the most physically challenging and impressive avian migrations by flying twice a year through the high plateau areas of the Himalayas, with some populations travelling between high altitude breeding grounds in China and lowland wintering areas in northern India. Despite their extraordinary flight performance and immensely interesting physiology and behaviour, neither the aerodynamic or physiological adaptations required to perform such feats are well understood. We will use miniature GPS tracking devices to provide detailed position and altitude during the flights so that we can identify their route in relation to the geographical topography and environmental conditions. This will also allow us to measure their rates of climb when migrating through the mountains. The bar-headed goose migration is exceptional for such a large bird as aerodynamic and biomechanical considerations suggest that as birds increase in body mass flight performance should deteriorate. Thus, bar-headed geese with a body mass of around 2.5 to 3.5 kg should only have a marginal physical capacity to sustain climbing flight even at sea level, and this ability should get worse as altitude increases due to the decrease in air density. By using 3-axis accelerometry we will be able to calculate the net aerodynamic forces acting on the body of the birds and monitor any changes in wingbeat frequency and relative wingbeat amplitude in response to changes in altitude and during the climbing flight. Their flights are also remarkable due to the physiological difficulties of sustaining any kind of exercise while coping with the harsh environmental conditions of the Tibetan plateau, especially the low ambient temperatures and the reduced availability of oxygen. Nevertheless, bar-headed geese have been recorded to fly between 4,000 m and 8,000 m, where partial pressures of oxygen are around 50% that of sea-level and temperatures can be as low as -20 C. We will measure the heart beat frequency of the birds during flights at different altitudes and estimate the maximum efforts expended during climbing flights in relation to their maximum expected capabilities. To place the remarkable migratory flights of the bar-headed goose in context, some 90% of avian migrations over land occur below 2000 m and the majority below 1000 m, which is well below the level of some of the main breeding lakes of the bar-headed goose (4,200 m to 4,718 m). We anticipate that the geographical barrier of the Himalayas should force these relatively large birds to fly close to the limits of their cardiac, muscular, respiratory and aerodynamic abilities. Indeed, this proposal will address the hypothesis that these migratory climbing flights may only by possible with the assistance of favourable up currents of air due to weather fronts or topographical reflections. Recent developments in electronic dataloggers now make it possible to measure both physical and physiological aspects of flight behaviour in free-flying birds rather than in animals constrained by captive conditions. Access to free-flying bar-headed geese would provide a unique opportunity to study the flight biology of a relatively large bird pushed to the extremes of its performance.

Technical Summary

We propose to undertake the first detailed scientific studies into the flight biology, migratory physiology and energetics of bar-headed geese (Anser indicus) in the wild using the latest electronic dataloggering technology. Ultimately, we will address the question of where are the limits to sustainable avian flight performance at high altitudes? In particular, how do larger species cope during flight with the combined effects of reduced air density, low oxygen availability and decreased temperature? The bar-headed goose performs one of the most physically challenging and impressive avian migrations by flying twice a year through the high plateau areas of the Himalayas. We will use miniature GPS tracking devices to provide detailed position and altitude during the flights so that we can identify their route in relation to the geographical topography and environmental conditions. This will also allow us to measure their maximum rates of climb when migrating through the mountains. The bar-headed goose should only have a marginal physical capacity to sustain climbing flight even at sea level, and this ability should get worse as altitude increases due to the decrease in air density. By using 3-axis accelerometry we will be able to calculate the net aerodynamic forces acting on the body of the birds and monitor any changes in wingbeat frequency and relative wingbeat amplitude in response to changes in altitude. Bar-headed geese have been recorded to fly over 6,000 m, where partial pressures of oxygen are around 50% that of sea-level and temperatures can be as low as -20 degrees centigrade. We will measure the heart beat frequency of the birds during flights at different altitudes and estimate the maximum efforts expended during climbing flights. This proposal will address the hypothesis that these migratory climbing flights may only by possible with the assistance of favourable up currents of air due to weather fronts or topographical reflections.

Publications

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Butler PJ (2010) High fliers: the physiology of bar-headed geese. in Comparative biochemistry and physiology. Part A, Molecular & integrative physiology

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Bourouiba L (2010) Spatial dynamics of bar-headed geese migration in the context of H5N1. in Journal of the Royal Society, Interface

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Bishop C (2013) Integration of exercise response and allometric scaling in endotherms in Journal of Theoretical Biology

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Scott GR (2015) How bar-headed geese fly over the Himalayas. in Physiology (Bethesda, Md.)

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Hawkes LA (2011) The trans-Himalayan flights of bar-headed geese (Anser indicus). in Proceedings of the National Academy of Sciences of the United States of America

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Hawkes L (2013) The paradox of extreme high-altitude migration in bar-headed geese Anser indicus in Proceedings of the Royal Society B: Biological Sciences

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Spivey RJ (2014) An implantable instrument for studying the long-term flight biology of migratory birds. in The Review of scientific instruments

 
Description 1) We tracked bar-headed geese (Anser indicus) flying over 3,000 km from Mongolia to India and back again. We showed that they could fly from sea level in India and then up and over the Himalayan Mountains, in a single 7 hour flight rising 5,000m in altitude.
2) We show that they seldom have the opportunity to make favorable use of tailwinds and that they make migratory progress in various wind conditions.
3) We show that these birds often fly at night and, contrary to previous beliefs, they tend to stay within 500m of the ground, or even within 100m when flying across the Tibetan Plateau, and only fly as high as is necessary.
4) We took swabs and blood to monitor the occurrence of avian influenza (H5N1) in collaboration with scientists from the US Geological Survey and the UN Food and Agriculture Organization.
5) We developed sophisticated data loggers that were implanted into bar-headed geese and successfully monitored heart rate, triaxial accelerometry, body temperature and atmospheric pressure.
6) We developed a theoretical understanding of a single unifying relationship between the rate of oxygen consumption and heart rate for birds and mammals.
7) We developed a theoretical model for interpreting body-mounted accelerometers placed on flying animals in terms of the ability to analyze power output.
8) We uncover a steep relationship between heart rate and wing beat frequency (wing beats raised to the exponent 3.5) and estimated metabolic power and wing beat frequency (wing beats raised to the estimated exponent 7) of migratory bar-headed geese.
9) We find that flight costs increase more rapidly than anticipated as air density declines, overturning prevailing expectations that this species should maintain high altitude flight when traversing the Himalayas.
10) We show for the first time that large, continuously flapping birds, such as geese, can make occasional use of updrafts of air generated by mountain ridges (orographic lift) deflecting the prevailing wind.
11) We conclude that the most economical method for flying through large mountain regions is to follow a 'roller coaster' strategy, of tracking the underlying terrain and discarding large altitude gains only to recoup them later in the flight with occasional benefits from orographic lift. Flying at night will also bring the benefits of increased oxygen availability and aerodynamic lift production due to the increased air density.
Exploitation Route 1) We expect that other scientists will find that many species of birds are making use of the benefits of higher air density, particularly when in mountainous areas, by flying relatively low to the ground and/or flying at night.
2) We expect to see other scientists studying the link between wing beat frequency and heart rate. This has the potential for enhancing our interpretation of the relative flight performance of different species and provides possible tools for the more detailed study of the evolution of different wing morphologies in flying animals.
3) Measurements of heart rate, in particular, have the potential to test some of the theoretical aerodynamic predictions, such as details of the U-shaped power curves of different species and whether birds really ever fly at their maximum range speeds.
Sectors Education,Environment,Other

URL http://barheadedgoose.bangor.ac.uk/about.php.en
 
Description The research results have been presented at international and national conferences and have been incorporated into postgraduate and graduate teaching degrees. Results have also been outputted in press releases and have made numerous media outlets, including the Indian Times and Telegraph, the Financial Times UK and a number of online avian and science websites, including the BBC and Sciencemag AAAS.
First Year Of Impact 2009
Sector Education,Environment,Other
Impact Types Cultural

 
Title Bar-headed goose tracks 
Description GPS Argos satellite tracking data from bar-headed geese (Anser indicus) tagged in either on their Indian wintering grounds or their Mongolian summer breeding grounds 
Type Of Material Database/Collection of data 
Year Produced 2010 
Provided To Others? Yes  
Impact Publication of paper on spatial dynamic modelling of pathogenic avian influenza. 
URL http://rsif.royalsocietypublishing.org/content/early/2010/05/13/rsif.2010.0126.short
 
Description Bangor University Science Festival 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Presentation of robotic bird display and scientific posters to stimulate discussion around bird flight and migratory journeys and the impact of Anthropogenic factors on bird behaviour and survival.
Year(s) Of Engagement Activity 2018
URL https://www.bangor.ac.uk/bangorsciencefestival/
 
Description HumaNature SEB special conference 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Two day conference between natural scientists and medical professionals to discuss the science of extreme adaptations and effects of the environment on biological systems. Significant discussion throughout the two days.
Year(s) Of Engagement Activity 2017
URL http://www.sebiology.org/events/event/humanature
 
Description Radio interviews 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Conducted around 20 media interviews with journalist from Radio (including live radio 4, Welsh Radio, German Radio, U.S. Radio and Newspapers (including UK Times, Delhi Times and Telegraph) and Online (including The Conversation, The Naked Scientist, The U.S. National Geographic and Science).
Year(s) Of Engagement Activity 2013,2015
URL http://science.sciencemag.org/content/347/6219/337.2.full