Protected areas have been identified as one of the most effective strategies for reducing biodiversity loss in a world where the negative effects of global change are increasing. However for species which migrate or which range beyond the borders of protected areas, these protected areas may only offer partial protection against the threats in the surrounding landscape. Understanding the role and limitations that protected areas can play in conserving threatened species can contribute to better conservation measures for species that may otherwise not benefit from more conventional conservation approaches. The Martial Eagle is a low-density apex predator currently declining across its African range. Changes in reporting rates from bird atlas surveys suggest declines of up to 60 % over the last 20 years (1987-1982 vs. 2007-2013) across South Africa. Worryingly, large protected areas were not immune to these declines. For instance reporting rates in Kruger National Park (KNP; ca. 20,000 km²), an area often considered a stronghold for Martial Eagles, recorded a 54 % decline in reporting rates. It is not clear what the major drivers of declines have been in South Africa, nor what is contributing to the declines in these large protected areas. In this thesis I study the ecology of Martial Eagles in KNP to improve our understanding of the threats they face and how these threats at various stages in their life cycle may be driving declines within protected areas where one would expect that the species should be well conserved. I hypothesised that the main driver of declines in protected areas is that juvenile Martial Eagles disperse beyond the borders of protected areas where they are at increased risk of unnatural mortality, thus leading to recruitment failure back into even the largest protected areas. To test this hypothesis, I fitted GPS tags to 9 juvenile eagles to understand their dispersal behaviour, an aspect of their life cycle for which no previous information existed, and to explore their survival rates. During a lengthy post fledging dependency phase (7 - 9 months) birds began making exploration trips that reached up to ca. 150 km from the nest site and beyond the borders of KNP. After dispersal onset, birds ranged widely up to 390 km from their nests covering areas that averaged ca. 6,500 km²; protected areas covered only 55 % of this area. In contrast to my hypothesis survival rates did not appear particularly low; from monitoring successfully dispersed juveniles over 36 months in total, only one immature bird was confirmed to have died presumably due to natural causes. To understand adult habitat preference and ranging behaviour, which can inform habitat requirements for the species conservation, I fitted GPS tags to eight adult birds. Models of their habitat preference indicated that the species preferred to utilise areas within their home ranges that were in areas with greater tree cover, with areas of dense bush rather than open bush or grassland, amongst other important features. These results were important to identify potential threats, such as the loss of trees in Savannah's, which is currently occurring due to elephant damage and fire influences. The species held large territories (ca. 108 km²) constraining the maximum number of pairs that the Park is able to support (max. 185 possible pairs), however models of distribution suggest the available habitat in KNP likely supports ca. 60 - 70 breeding pairs. Two adult individuals never held territories and another two abandoned their territories during the course of the study. These individuals ranged widely (ca. 44,000 km²) suggesting a floater population exists in the region. The death of three of these four floater individuals (two persecutions and an electrocution) indicates that adults are particularly at risk of mortality during these wide-ranging movements beyond protected area boundaries. Two natural mortalities of territorial birds within the park were also recorded. Overall therefore, despite our relatively small sample size, adult birds do appear to have worryingly low survival rates. Because my sample size of both adults and juveniles/immatures was relatively small (adults = 8, juveniles = 9), their movements may not be fully representative of the entire population. Therefore, I additionally modelled the distribution of Martial Eagles using independent sightings data to describe suitable areas for the species both within the KNP and adjacent areas (within ca. 400 km of the park). Identifying these areas provides conservation managers with more information to ensure adequate conservation measures are in place for this species in these areas. At least 29 % of KNP was predicted to be suitable for Martial Eagles, while neighbouring regions in Mozambique and Swaziland were also predicted to be highly suitable for the species. Given the adult mortalities and general scarcity of Martial Eagles in Mozambique the area may act as a population sink for KNP birds. Lastly, I compared current reproductive parameters to those reported in a considerable number of other studies on the species both within KNP and elsewhere. Productivity recorded during this study was lower than any previously recorded estimate. Using a population model, I show that current productivity within KNP is sufficiently low to have been solely responsible for the known levels of decline there, without the need to invoke any other contributory factors. A high hatching failure rate was mostly responsible for the low productivity. However, it is important to note that at least two of the three years of data collection occurred during low (drought) rainfall years, which may have constrained breeding, and thus may not be reflective of productivity levels more generally over the recent longer term. My research helps identify the most likely drivers of population declines in KNP, suggesting that elevated adult mortality and lower productivity may be the key factors. Drivers of low productivity require further investigation, however it is likely that changes in habitat quality or climate may be impacting on the species within KNP. The study also highlighted the difficulty of conserving wideranging and threatened species in protected areas, which may be prone to high mortality in the surrounding landscape. This research is therefore applicable to a number of species that range widely from KNP e.g. vultures, or migratory eagles. The research indicates that protected areas alone are unlikely to conserve these species and that additional conservation measures, such as education programmes, or trans boundary policy should be put in place to realise successful conservation for these species.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/25522 |
| Date | January 2017 |
| Creators | Van Eeden, Rowen |
| Contributors | Amar, Arjun, Whitfield, D Phil |
| Publisher | University of Cape Town, Faculty of Science, Percy FitzPatrick Institute of African Ornithology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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