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Vultures respond to challenges of near-ground thermal soaring by varying bank angle

Hannah J. Williams, Olivier Duriez, Mark Holton Orcid Logo, Giacomo Dell'Omo, Rory P. Wilson, Emily Shepard Orcid Logo

The Journal of Experimental Biology, Start page: jeb.174995

Swansea University Authors: Mark Holton Orcid Logo, Emily Shepard Orcid Logo

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DOI (Published version): 10.1242/jeb.174995

Abstract

Many large birds rely on thermal soaring flight to travel cross-country. As such, they are under selective pressure to minimise the time spent gaining altitude in thermal updrafts. Birds should be able to maximise their climb rates by maintaining a position close to the thermal core through careful...

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Published in: The Journal of Experimental Biology
ISSN: 0022-0949 1477-9145
Published: 2018
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URI: https://cronfa.swan.ac.uk/Record/cronfa45287
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spelling 2018-12-21T15:39:15.6653043 v2 45287 2018-10-29 Vultures respond to challenges of near-ground thermal soaring by varying bank angle 0e1d89d0cc934a740dcd0a873aed178e 0000-0001-8834-3283 Mark Holton Mark Holton true false 54729295145aa1ea56d176818d51ed6a 0000-0001-7325-6398 Emily Shepard Emily Shepard true false 2018-10-29 SBI Many large birds rely on thermal soaring flight to travel cross-country. As such, they are under selective pressure to minimise the time spent gaining altitude in thermal updrafts. Birds should be able to maximise their climb rates by maintaining a position close to the thermal core through careful selection of bank angle and airspeed, however, there have been few direct measurements of either parameter. Here we apply a novel methodology to quantify the bank angles selected by soaring birds using on-board magnetometers. We couple these data with airspeed measurements to parameterise the soaring envelope of two species of Gyps vulture, from which it is possible to predict “optimal” bank angles. Our results show that these large birds respond to the challenges of gaining altitude in the initial phase of the climb, where thermal updrafts are weak and narrow, by adopting relatively high, and conserved, bank angles (25-35°). The angle of bank decreased with increasing altitude, in a manner that was broadly consistent with a strategy of maximising the rate of climb. However, the lift coefficients estimated in our study were lower than those predicted by theoretical models and wind-tunnel studies. Overall, our results highlight how the relevant currency for soaring performance changes within individual climbs; when thermal radius is limiting, birds vary bank angle and maintain a constant airspeed, but speed increases later in the climb in order to respond to decreasing air density. Journal Article The Journal of Experimental Biology jeb.174995 0022-0949 1477-9145 31 12 2018 2018-12-31 10.1242/jeb.174995 COLLEGE NANME Biosciences COLLEGE CODE SBI Swansea University 2018-12-21T15:39:15.6653043 2018-10-29T18:25:23.2972650 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Biosciences Hannah J. Williams 1 Olivier Duriez 2 Mark Holton 0000-0001-8834-3283 3 Giacomo Dell'Omo 4 Rory P. Wilson 5 Emily Shepard 0000-0001-7325-6398 6 0045287-29102018182650.pdf JEB_Thermalsoaringbirdsmodulatebankangle_withfigs.pdf 2018-10-29T18:26:50.4900000 Output 1093973 application/pdf Accepted Manuscript true 2019-10-18T00:00:00.0000000 true eng
title Vultures respond to challenges of near-ground thermal soaring by varying bank angle
spellingShingle Vultures respond to challenges of near-ground thermal soaring by varying bank angle
Mark Holton
Emily Shepard
title_short Vultures respond to challenges of near-ground thermal soaring by varying bank angle
title_full Vultures respond to challenges of near-ground thermal soaring by varying bank angle
title_fullStr Vultures respond to challenges of near-ground thermal soaring by varying bank angle
title_full_unstemmed Vultures respond to challenges of near-ground thermal soaring by varying bank angle
title_sort Vultures respond to challenges of near-ground thermal soaring by varying bank angle
author_id_str_mv 0e1d89d0cc934a740dcd0a873aed178e
54729295145aa1ea56d176818d51ed6a
author_id_fullname_str_mv 0e1d89d0cc934a740dcd0a873aed178e_***_Mark Holton
54729295145aa1ea56d176818d51ed6a_***_Emily Shepard
author Mark Holton
Emily Shepard
author2 Hannah J. Williams
Olivier Duriez
Mark Holton
Giacomo Dell'Omo
Rory P. Wilson
Emily Shepard
format Journal article
container_title The Journal of Experimental Biology
container_start_page jeb.174995
publishDate 2018
institution Swansea University
issn 0022-0949
1477-9145
doi_str_mv 10.1242/jeb.174995
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Biosciences{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Biosciences
document_store_str 1
active_str 0
description Many large birds rely on thermal soaring flight to travel cross-country. As such, they are under selective pressure to minimise the time spent gaining altitude in thermal updrafts. Birds should be able to maximise their climb rates by maintaining a position close to the thermal core through careful selection of bank angle and airspeed, however, there have been few direct measurements of either parameter. Here we apply a novel methodology to quantify the bank angles selected by soaring birds using on-board magnetometers. We couple these data with airspeed measurements to parameterise the soaring envelope of two species of Gyps vulture, from which it is possible to predict “optimal” bank angles. Our results show that these large birds respond to the challenges of gaining altitude in the initial phase of the climb, where thermal updrafts are weak and narrow, by adopting relatively high, and conserved, bank angles (25-35°). The angle of bank decreased with increasing altitude, in a manner that was broadly consistent with a strategy of maximising the rate of climb. However, the lift coefficients estimated in our study were lower than those predicted by theoretical models and wind-tunnel studies. Overall, our results highlight how the relevant currency for soaring performance changes within individual climbs; when thermal radius is limiting, birds vary bank angle and maintain a constant airspeed, but speed increases later in the climb in order to respond to decreasing air density.
published_date 2018-12-31T03:57:01Z
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score 11.037581

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