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Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps). / Emily Laura Cairns Shephard

Swansea University Author: Emily Laura Cairns Shephard

Abstract

Predators are frequently involved in an arms race with their prey, with improved abilities on one side demanding compensatory improvements on the other. Those that breathe air but forage underwater are faced with the additional challenge of capturing prey in a medium where their own capacity to rema...

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Published: 2009
Institution: Swansea University
Degree level: Doctoral
Degree name: Ph.D
URI: https://cronfa.swan.ac.uk/Record/cronfa42298
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last_indexed 2018-08-03T10:09:46Z
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spelling 2018-08-02T16:24:28.7293887 v2 42298 2018-08-02 Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps). 4f1ee6114f4c14fa2a18a66526710665 NULL Emily Laura Cairns Shephard Emily Laura Cairns Shephard true true 2018-08-02 Predators are frequently involved in an arms race with their prey, with improved abilities on one side demanding compensatory improvements on the other. Those that breathe air but forage underwater are faced with the additional challenge of capturing prey in a medium where their own capacity to remain is limited. This thesis examines some of the strategies used by my model organism, the imperial shag (Phalacrocorax atriceps) to enhance its foraging efficiency. I did this by using recent developments in animal-attached technology to measure the patterns and costs of bird behaviour during foraging at a fine-scale. Time appeared to be of the essence for these birds, as their movements were consistent with a strategy to maximise the rate of energy gain. Male and female shags were found to forage at depths where their foraging efficiency was maximised, which manifested itself in the horizontal segregation of male and female foraging areas. Analysis of the mechanical power used underwater suggested that these birds may be limited in the burst speeds they can produce at shallow depths; as the greater the power required to counteract their buoyancy the less is available for prey pursuit. Finally, analysis of the fine-scale tortuosity in the foraging movements of imperial shags revealed that the distribution of their prey was not aggregated at the scales over which they forage. Nevertheless, tortuosity was a good indicator of prey ingestion rates and revealed that shags adjusted their movements to recent prey encounter within both prey-searching and resting phases. This work indicates that imperial shags have an extensive armoury of strategies by which they may increase their efficiency as underwater predators, and methods used and refined in this thesis mean that users are now well-equipped to investigate them. E-Thesis Ecology. 31 12 2009 2009-12-31 COLLEGE NANME Biosciences COLLEGE CODE Swansea University Doctoral Ph.D 2018-08-02T16:24:28.7293887 2018-08-02T16:24:28.7293887 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Biosciences Emily Laura Cairns Shephard NULL 1 0042298-02082018162443.pdf 10798006.pdf 2018-08-02T16:24:43.4870000 Output 15497238 application/pdf E-Thesis true 2018-08-02T16:24:43.4870000 false
title Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
spellingShingle Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
Emily Laura Cairns Shephard
title_short Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
title_full Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
title_fullStr Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
title_full_unstemmed Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
title_sort Strategies for efficient foraging in a deep-diving bird; the imperial shag (Phalacrocorax atriceps).
author_id_str_mv 4f1ee6114f4c14fa2a18a66526710665
author_id_fullname_str_mv 4f1ee6114f4c14fa2a18a66526710665_***_Emily Laura Cairns Shephard
author Emily Laura Cairns Shephard
author2 Emily Laura Cairns Shephard
format E-Thesis
publishDate 2009
institution Swansea University
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 Predators are frequently involved in an arms race with their prey, with improved abilities on one side demanding compensatory improvements on the other. Those that breathe air but forage underwater are faced with the additional challenge of capturing prey in a medium where their own capacity to remain is limited. This thesis examines some of the strategies used by my model organism, the imperial shag (Phalacrocorax atriceps) to enhance its foraging efficiency. I did this by using recent developments in animal-attached technology to measure the patterns and costs of bird behaviour during foraging at a fine-scale. Time appeared to be of the essence for these birds, as their movements were consistent with a strategy to maximise the rate of energy gain. Male and female shags were found to forage at depths where their foraging efficiency was maximised, which manifested itself in the horizontal segregation of male and female foraging areas. Analysis of the mechanical power used underwater suggested that these birds may be limited in the burst speeds they can produce at shallow depths; as the greater the power required to counteract their buoyancy the less is available for prey pursuit. Finally, analysis of the fine-scale tortuosity in the foraging movements of imperial shags revealed that the distribution of their prey was not aggregated at the scales over which they forage. Nevertheless, tortuosity was a good indicator of prey ingestion rates and revealed that shags adjusted their movements to recent prey encounter within both prey-searching and resting phases. This work indicates that imperial shags have an extensive armoury of strategies by which they may increase their efficiency as underwater predators, and methods used and refined in this thesis mean that users are now well-equipped to investigate them.
published_date 2009-12-31T03:52:41Z
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score 11.017797

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