Grouping Behaviour and Anti-Predator Responses in the Helmeted Guineafowl Numida meleagris

Simple Summary This study deals with the role of predator pressure on group formation in the Helmeted Guineafowl, a large sub-Saharan highly social galliform. We focused on a population from South Africa exposed to the frequent chase of both aerial and terrestrial predators, namely, eagles and jackals, recording prey and predator behaviour along with the outcome of predatory encounters. While all attacks were directed to prey aggregates rather than lone individuals, a tendency for chasing groups of a larger size seemingly emerged in jackals. However, unlike aerial predators, these do not seem to induce high fear in guineafowl, eliciting hardly predictable anti-predator responses. This arguably suggests that these galliforms perceive eagles and jackals differently despite the comparable hunting success. While the high predator-induced fear points to a well-established predator-prey system in the case of aerial predators, jackals, mostly carrion eaters, are perceived as a minor threat accounting for the failure in eliciting a well-defined defensive behaviour.Abstract Little is known about landbird group dynamics in response to predation. Here, we describe the interactions between the Helmeted Guineafowl (Numida meleagris) and its predators regarding the survival advantages grouping behaviour may provide. Livestream webcam observations were conducted in Madikwe Game Reserve (South Africa) from August 2020 to August 2021. Emphasis was placed on predator-prey interaction and its effect on group size and structure in a spatial framework. We hypothesise that while grouping is crucial for a number of daily activities in this highly social species, it might turn into a higher predatory pressure. We found, indeed, that the probability of attacks by black-backed jackals (Lupulella mesomelas) significantly increased with guineafowl group size, unlike what happened with raptors. Moreover, when attacked by jackals, the birds responded by standing close to each other. These results suggest, in line with the proposed hypothesis, that a trade-off occurs between the defensive function of grouping in this galliform and the probability of jackal attack that increases as a function of prey group size. Nevertheless, we argue that Helmeted Guineafowl cooperative social groups also play a role as a defensive strategy against predators, with the many-eyes and dilution effects likely compensating for the higher predatory pressure.