Goose vigilance and group size on golf courses in Cape Town (2015)

Vigilance is amongst the most universal of anti-predator strategies and commonly declines with increasing group size. We experimentally manipulated predation risk in a system with a known relationship between group size and vigilance levels to explore whether this relationship changes in response to elevated predation risk. We investigated the vigilance levels of Egyptian geese Alopochen aegyptiaca at eight golf courses in the Western Cape, South Africa, to assess the perception of and reaction to predation risk. We manipulated predation risk by introducing trained Harris’s hawks Parabuteo unicintus where avian predation was otherwise low or absent. The study confirmed the typical reduction in vigilance with group size on control sites, where the risk of predation is low. However, at experimental sites with elevated predation risk, a positive relationship between vigilance and group size was observed. We hypothesize that the mechanism for this relationship might be linked to social information transfer via copying behavior and manipulation to induce vigilance. Thus, larger groups will have a higher probability of containing individuals with experience of elevated predation risk and their increased vigilance behavior is copied by naïve individuals. This prediction is based on the intended outcome of introducing avian predation to make the geese feel less safe and to eventually leave the site as a management tool for controlling nuisance geese.<br>

警戒行为（vigilance）是最为普遍的反捕食策略之一，且通常随种群规模扩大而降低。本研究在已明确种群规模与警戒行为水平间存在关联的研究系统中，通过实验操控捕食风险水平，旨在探究该关联是否会随捕食风险升高而发生变化。我们于南非西开普省的8处高尔夫球场开展野外调查，记录埃及雁（Alopochen aegyptiaca）的警戒行为水平，以评估其对捕食风险的感知与响应方式。在原本鸟类捕食压力较低或无鸟类捕食的区域，我们通过引入经过驯化的哈里斯鹰（Parabuteo unicintus）来人为提升捕食风险水平。本研究证实，在捕食风险较低的对照组样地中，警戒行为随种群规模扩大而降低的经典模式成立。然而在捕食风险升高的实验组样地中，却观测到警戒行为与种群规模呈正相关的关系。我们推测，该关联的潜在机制可能与通过模仿行为传递社会信息，以及诱导警戒行为的实验操控过程有关：种群规模更大的群体更有可能包含曾经历过高捕食风险的个体，而这些个体增强的警戒行为会被无相关经验的个体所模仿。该预测基于引入鸟类捕食的预设目标：将其作为管控扰民野生雁的管理手段，通过降低雁群的安全感，最终促使其主动离开目标区域。