The threat of terrestrial predators to mainland penguin colonies: searching for sustainable solutions

Rhoda, Linden

The threat of terrestrial predators to mainland penguin colonies: searching for sustainable solutions

Master Thesis

2023

Abstract

Anthropogenic activities including overexploitation of natural resources and the transformation of natural habitat have disturbed ecological systems and are increasingly challenging the natural persistence, movement, and interactions of wildlife populations. On the Cape Peninsula in South Africa, all large predators were extirpated to reduce threats to lives and livelihoods with the medium-sized caracal (Caracal caracal) emerging as the de facto apex predator. Overexploitation of Africa penguins (Spheniscus demersus), their prey and their island breeding sites in the south-western Cape resulted in a rapid decline in the African penguin population and a shift in their distribution. This shift coincided with the establishment of at least four mainland colonies, one of which is on the Cape Peninsula. In this manner a Least Concern, abundant predator encountered an Endangered bird species poorly adapted to terrestrial predators, setting the scene for a conservation conflict in the Anthropocene. My goal in attempting to mitigate this conflict was to first collate all available data on mainland penguin colony demographics and to understand the relative threat posed by terrestrial predators such as caracal on their mortality. Secondly, I reviewed historical and current management interventions by conservation authorities to protect mainland colonies from terrestrial predators and assessed both their success in protecting penguins and their impacts on the predators. Having identified discrepancies amongst stakeholders in how best to manage the interface between penguins and predators I reviewed the potential non-lethal and lethal methods and used a standardised evaluation scoring system to identify those strategies with the most support. I then developed a management plan that integrates these strategies and provides the most sustainable solution for reducing supernumerary predation events while also offering conservation benefits to caracal. I made use of a qualitative triangulation approach for the evaluation of management techniques as this explores anecdotal data from case-studies alongside the individual experiences of environmental managers and experts in the field. Annual counts at mainland penguin colonies revealed that only two of the four colonies had persisted, and both had exhibited strong early growth and were now recognised as important breeding sites with high conservation status. Surprisingly both surviving mainland colonies were established in peri-urban areas with high levels of anthropogenic disturbance including vehicular collisions, and disturbance by domestic animals and people. Leopard (Panthera pardus pardus) and caracal were both identified as posing a significant threat to the viability of the Stony Point and Simon's Town penguin populations respectively. Both predators had engaged in supernumerary predation events, which have cumulatively resulted in the recorded deaths of at least 346 penguins over the last decade. In response to predations local statutory authorities have attempted numerous intervention strategies at both colonies. Remote camera traps proved effective at early detection and identifying species responsible, while physical barriers were effective at reducing access to colonies. Capture and collaring of caracal on the Peninsula with follow-up monitoring of movement adjacent to the colony proved ineffective as the caracal readily evaded staff deployed to deter them. Relocation of caracal within the Peninsula has had limited success as only one individual established a stable territory far from the colony, while the remaining cats either returned to the colony or died in vehicular collisions. The average time between supernumerary predation events following relocations or the euthanasia of caracal was approximately six months. A total of 17 primary mitigation management interventions were evaluated by key stakeholders with three having high levels of support visà-vis: cameras for early detection of potential predators, physical barriers to deter entrance to the colony or funnel predators into capture cages for translocation to other protected areas within the City of Cape Town (CoCT). Together with local conservation authorities and managers these three interventions were then integrated into a management plan with standard operating procedures and a decision flow chart so as to 1) greatly reduce predation on penguins by terrestrial predators, 2) prioritise non-lethal interventions including the development of a translocation plan to CoCT nature reserves, 3) ensure the plan aligns with current local and international (IUCN) policy, 4) be cost effective and practically achievable with the resources available, and 5) have broad public, stakeholder, and statutory acceptability. Together these interventions provide a solution to a classic conservation conflict in the Anthropocene and can serve as a suitable template for the management of Least Concern predators impacted by urban development both in South Africa and elsewhere in the world.

Keywords

Biological Sciences

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