Carrion represents an unpredictable and widely distributed primary food source for vultures and other avian scavengers. Avian scavengers in African savanna ecosystems are reported to rely exclusively on visual stimuli to locate carcasses. However, carnivores’ predation of large mammalian herbivores and subsequent competition for access to the carcass can result in considerable noise, often audible over long distances and for prolonged periods. Vultures and other avian scavengers may therefore detect and respond to these auditory cues, as do the mammalian carnivores alongside which vultures have coevolved, but this has not been investigated to date. Working in the Serengeti ecosystem, Tanzania, we used diurnal auditory broadcasts to simulate predation and competitive carnivore feeding interactions. Based on the current understanding of avian scavenger ecology, we hypothesized that avian responses to call‐in stations would be evoked exclusively by visual, rather than auditory, cues. We therefore predicted that (a) the arrival of avian scavengers at call‐in stations should be preceded and facilitated by mammalian carnivores and that (b) the arrival of avian scavengers would be positively correlated with the number of mammalian scavengers present, which would increase detectability. We recorded 482 birds during 122 separate playback events. In 22% of these instances, avian scavengers arrived first, ruling out responses based exclusively on visual observations of mammalian carnivores, thereby contradicting our first prediction. Furthermore, the first avian arrivals at survey sessions were inversely related to the number of hyenas and jackals present, contradicting our second prediction. Since no bait or carcasses were used during the experiments, these responses are indicative of the birds’ ability to detect and respond to audio stimuli. Our findings challenge the current consensus of sensory perception and foraging in these species and provide evidence that avian scavengers have the ability to use sound to locate food resources.
Many animal populations are exposed to disturbance originating from human activities. In response to human disturbance, certain animals display a variety of potentially costly behavioural responses, such as increased antipredator behaviour or relocation to new areas. In contrast, other animals seemingly thrive in the presence of humans and benefit from human‐derived resources. Flight initiation distance (FID: the distance between predator and prey when prey starts to flee) is a measure commonly used to assess animals’ tolerance to humans. In this study, we tested how FID changes in relation to human presence in two hyrax species in Serengeti National Park. Hyraxes living on kopjes (rock outcrops) among human settlements showed a significantly shorter FID than hyraxes living on kopjes without human settlements. In addition, we found that hyraxes feeding before the experiment had shorter FID than hyraxes resting or being vigilant, and hyraxes disturbed during the early morning had shorter FID than hyraxes disturbed during late morning. We did not find any significant effects of group size or species composition on FID. Our results suggest that hyraxes living in the presence of humans are habituated and are not adversely affected by human settlements.
Understanding the factors affecting a species’ population size is crucial for conservation initiatives. Hyraxes are small, gregarious animals, predominantly found on kopjes (rock outcrops) and thus form metapopulation communities. In Tanzania, two species of hyraxes inhabit Serengeti National Park, the rock hyrax Procavia capensis johnstoni and bush hyrax Heterohyrax brucei. This study focuses on the factors that affect hyrax population size, including factors such as human presence, habitat type, kopje size and kopje height. We found that larger and taller kopjes tended to have more hyraxes than smaller ones, while kopjes in wooded grassland had more hyraxes than kopjes in grassland. Human presence often affects species negatively, but in the case of hyraxes, we found that kopjes with human presence had larger populations than kopjes without humans. We discuss possible explanations for this and suggest that human presence is related to fewer predators and higher food availability.
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