American Society of Naturalists

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“Information about predators varies across an Amazonian rainforest as a result of sentinel species distribution”

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Ettore Camerlenghi, Paola Tellaroli, Matteo Griggio, and Ari E. Martínez (Nov 2019)

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The distribution of different alarm calling species drives the patchiness of predator information in a rainforest

Female Bluish-slate Antshrike (<i>Thamnomanes schistogynus</i>).<br />(Credit: Eliseo Parra of <a href=""></a>)
Female Bluish-slate Antshrike (Thamnomanes schistogynus).
(Credit: Eliseo Parra of

Predation risk is considered one of the main drivers of the formation of mixed-species flocks of birds, in which different species aggregate, forage and move together in the forest. In many cases, certain species are exceptionally vigilant against predators and emit alarm calls upon detecting ambush predators. These species are considered a key element in allowing other flocking species to exploit otherwise “risky habitats”. The presence of these “sentinel species” allows other species to navigate a forested version of a landscape of fear.

Southeastern Peruvian Amazon.<br />(Credit: Eliseo Parra of <a href=""></a>)
Southeastern Peruvian Amazon.
(Credit: Eliseo Parra of

In the Amazon lowland rainforests of southeastern Peru, two different sentinel bird species occupy different types of habitats across tierra firme forest without overlapping. The Bluish-slate Antshrike specializes in patches of early successional stage, such as those gaps created by fallen trees. The Dusky-throated Antshrike occupies undisturbed areas of primary forest. Camerlenghi and colleagues showed that other flocking bird species (which can associate with either of these sentinel species) perceive the alarm calls given by the Bluish-slate as more reliable than those emitted by the Dusky-throated and react accordingly. Thus, not only do forest habitats inhabited by flocks differ structurally, but they may also differ in the quality of predator information provided by alarm calling species that inhabit them, with potential effects for the long-term survival of flock mates.

Male Dusky-throated Antshrike (<i>Thamnomanes ardesiacus</i>).<br />(Credit: Eliseo Parra of <a href=""></a>)
Male Dusky-throated Antshrike (Thamnomanes ardesiacus).
(Credit: Eliseo Parra of


Information about predation risk is of fundamental value in biological communities. As many prey species have shared predators, eavesdropping on other species’ alarms is a widely recognized mechanism underlying the formation of mixed-species groups. However, information transfer may vary both across and within groups because some species provide higher quality information about predators than others. We tested this phenomenon in Amazonian understory mixed-species flocks of birds in which two sentinel species, the Bluish-slate Antshrike (Thamnomanes schistogynus) and the Dusky-throated Antshrike (Thamnomanes ardesiacus) occupy different habitats and provide alarm calls that are used by eavesdropping flock mates. In a playback experiment, both associate species responded significantly more strongly to alarm calls from the same sentinel species, reflecting the greater reliability of information about predator threats that could affect survival and habitat choice. Our work provides evidence of a repeated asymmetry across space in the available information about threats.