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No universal support for solar glare as an evolutionary driver of malar stripes in falcons
The paired dark malar or moustachial stripes of falcons (Falco spp.) are putatively adaptive plumage features whose function and evolutionary significance are poorly understood, and have rarely been investigated in published literature. A popular hypothesis for the function of falcon malar stripes i...
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| Format: | Thesis |
| Language: | English |
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Department of Biological Sciences
2023
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| _version_ | 1867613200939220992 |
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| access_status_str | Open Access |
| author | Vrettos, Michelle |
| author2 | Amar, Arjun |
| author_browse | Amar, Arjun Vrettos, Michelle |
| author_facet | Amar, Arjun Vrettos, Michelle |
| author_sort | Vrettos, Michelle |
| collection | Thesis |
| description | The paired dark malar or moustachial stripes of falcons (Falco spp.) are putatively adaptive plumage features whose function and evolutionary significance are poorly understood, and have rarely been investigated in published literature. A popular hypothesis for the function of falcon malar stripes is that they serve as antiglare devices, with the dark pigment absorbing visionimpeding solar glare and thereby improving the falcon's ability to visually detect and target prey in bright conditions. Correlative evidence from Peregrine Falcons (Falco peregrinus) provides support for this hypothesis, with a previous study finding that the size and prominence of malar stripes in this species correlate positively with solar radiation across the species' geographic range. In the present study, I extend the methodology used in this previous research to all extant species in the genus Falco, to determine both whether other falcon species display similar intraspecific trends, and whether differences in solar radiation conditions, in conjunction with species ecology, explain interspecific variation in falcon malar stripe characteristics. My results indicated that malar stripe characteristics were not positively related to solar radiation in the majority of species, with only the Peregrine Falcon showing reliable trends towards larger and darker malar stripes in individuals inhabiting regions of higher solar radiation. Likewise, solar radiation was not positively related to interspecific variation in falcon malar stripe characteristics, even after accounting for differences in body size, agility, prey base, and habitat between species. These results suggest that falcon malar stripes do not universally function as antiglare devices, at least in species other than the Peregrine Falcon. Malar stripes thus likely evolved in falcons for a different purpose (such as crypsis or social signaling), but may have become exapted for solar glare reduction in Peregrine Falcons owing to the species' cosmopolitan distribution and high degree of specialization on agile bird prey. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/38201 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:32:21.936Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2023 |
| publishDateRange | 2023 |
| publishDateSort | 2023 |
| publisher | Department of Biological Sciences |
| publisherStr | Department of Biological Sciences |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/38201 No universal support for solar glare as an evolutionary driver of malar stripes in falcons Vrettos, Michelle Amar, Arjun Marais Patrick Biological Sciences The paired dark malar or moustachial stripes of falcons (Falco spp.) are putatively adaptive plumage features whose function and evolutionary significance are poorly understood, and have rarely been investigated in published literature. A popular hypothesis for the function of falcon malar stripes is that they serve as antiglare devices, with the dark pigment absorbing visionimpeding solar glare and thereby improving the falcon's ability to visually detect and target prey in bright conditions. Correlative evidence from Peregrine Falcons (Falco peregrinus) provides support for this hypothesis, with a previous study finding that the size and prominence of malar stripes in this species correlate positively with solar radiation across the species' geographic range. In the present study, I extend the methodology used in this previous research to all extant species in the genus Falco, to determine both whether other falcon species display similar intraspecific trends, and whether differences in solar radiation conditions, in conjunction with species ecology, explain interspecific variation in falcon malar stripe characteristics. My results indicated that malar stripe characteristics were not positively related to solar radiation in the majority of species, with only the Peregrine Falcon showing reliable trends towards larger and darker malar stripes in individuals inhabiting regions of higher solar radiation. Likewise, solar radiation was not positively related to interspecific variation in falcon malar stripe characteristics, even after accounting for differences in body size, agility, prey base, and habitat between species. These results suggest that falcon malar stripes do not universally function as antiglare devices, at least in species other than the Peregrine Falcon. Malar stripes thus likely evolved in falcons for a different purpose (such as crypsis or social signaling), but may have become exapted for solar glare reduction in Peregrine Falcons owing to the species' cosmopolitan distribution and high degree of specialization on agile bird prey. 2023-07-30T09:49:39Z 2023-07-30T09:49:39Z 2023 2023-07-30T09:48:58Z Master Thesis Masters MSc http://hdl.handle.net/11427/38201 eng application/pdf Department of Biological Sciences Faculty of Science |
| spellingShingle | Biological Sciences Vrettos, Michelle No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| thesis_degree_str | Master's |
| title | No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| title_full | No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| title_fullStr | No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| title_full_unstemmed | No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| title_short | No universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| title_sort | no universal support for solar glare as an evolutionary driver of malar stripes in falcons |
| topic | Biological Sciences |
| url | http://hdl.handle.net/11427/38201 |
| work_keys_str_mv | AT vrettosmichelle nouniversalsupportforsolarglareasanevolutionarydriverofmalarstripesinfalcons |