- Title
- Trophic ecology and breeding success of Brown Skuas (Catharacta antarctica)
- Creator
- Walker, Tegan
- Subject
- Birds -- Conservation
- Subject
- Birds -- Ecology
- Subject
- Birds -- Behavior -- Evolution
- Date Issued
- 2024-04
- Date
- 2024-04
- Type
- Master's theses
- Type
- text
- Identifier
- http://hdl.handle.net/10948/64437
- Identifier
- vital:73710
- Description
- Invasive species can impact island ecosystem processes by altering species interactions through direct competition for the same resources or by predation on insular species. Seabirds on sub-Antarctic islands are naïve to any new predators and are most at risk of local extirpation. Successful eradications of invasive mammals have yielded positive ecological responses from several seabird species. On sub-Antarctic Marion Island, populations of burrowing petrels, largely targeted by Feral Cats Felis catus, have indicated slow recovery despite the successful eradication of cats in the early 1990s. House Mice Mus musculus, have since proliferated on Marion Island, aided by a warmer climate, and are severely impacting several defenceless populations of burrowing petrels. In this thesis, I investigated the contemporary breeding productivity and diet of Brown Skuas Catharacta antarctica. At Marion Island, Brown Skua breeding productivity was associated to diet, which varied between years. Skuas feeding mostly on burrowing petrels exhibited higher breeding success than pairs mostly feeding on penguins. Higher contributions of burrowing petrels were seen in the contemporary diet of skuas compared to previous diet work. The importance of penguin prey compared to their 1980 and 2010/11 diet, was largely reduced during the 2021/22 and 2022/23 breeding seasons (53 and 51%, respectively) despite a historically high dependence on this prey (78% in 1980 and 67% in 2010/11). Penguin populations have been decreasing at the island and this may be reflected in the current skua diet. Breeding productivity was not influenced by the other factors tested, i.e. weather data (daily minimum, average and maximum air temperature; daily minimum, average, maximum wind speed; daily precipitation), distance to closest penguin colony, species of penguin or number of conspecifics in a 100 m radius around the nest. Brown Skuas breeding on Marion, Gough and Mayes islands were also used as biosamplers of burrowing petrels. These birds form a large part of the skua diet and are reflected in regurgitated skua pellets. Temporal comparisons for Marion Island indicated significant changes in burrowing petrel composition since the 1980s. Blue Petrels Halobaena caerulea and Salvin’s Prions Pachyptila salvini remained the highest contributors of skua pellets, but their proportions differed with three-fold increase in Blue Petrel and 25% decrease in Salvin’s Prion remains compared to previous studies. Further, my study indicated that smaller species of burrowing petrels such as the storm-petrels and diving petrels may be returning to Marion Island, 30 years after the eradication of cats. Pellet analyses at Marion, Gough and Mayes islands also indicated that skua diet may underrepresent larger species of petrels and soft-bodied prey. Despite these limitations, skua diet can indicate the presence of burrowing petrels during summer months, more so at Marion and Mayes islands than Gough Island, where pellet collection is difficult due to dense vegetation. Prey remains, such as wings in middens, may be a more appropriate method to investigate skua diet at Gough Island. Dominant burrowing petrels indicated by pellets at each island generally reflected the most abundant breeding species; Blue Petrels and Salvin’s Prions at Marion Island, Great Shearwaters Puffinus gravis and prion Pachyptila spp. at Gough Island, and Blue Petrels and Slender-billed Prions Pachyptila belcheri at Mayes Island. Pellets provide a non-invasive method for studying species of burrowing petrels that are challenging to monitor. This method is appropriate for studies conducted during summer months, while other studies (e.g., observations, camera traps, acoustic recordings and genetics) may be more reflective of the presence of burrowing species that breed in winter or could be used in combination with skua pellets during summer months. Population monitoring is an important part of conservation as it provides insights into population change. This thesis adds to the baseline data in terms of breeding productivity and updated trophic ecology of Brown Skuas, which will be used to inform the recovery of burrowing petrels once mice have been eradicated from Marion Island.
- Description
- Thesis (MSc) -- Faculty of Science, School of Environmental Sciences, 2024
- Format
- computer
- Format
- online resource
- Format
- application/pdf
- Format
- 1 online resource (xiv, 64 pages)
- Format
- Publisher
- Nelson Mandela University
- Publisher
- Faculty of Science
- Language
- English
- Rights
- Nelson Mandela University
- Rights
- All Rights Reserved
- Rights
- Open Access
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NMU School of Environmental Sciences
| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | SOURCE1 | Walker, T.pdf | 1 MB | Adobe Acrobat PDF | View Details Download |