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Predation is a strong ecological force that shapes animal communities through natural selection. Recent studies have shown the cascading effects of predation risk on ecosystems through changes in prey behavior. Minimizing predation risk is a central hypothesis that may explain why multiple prey species associate together. For example, birds that eavesdrop on sentinel species (alarm calling heterospecifics) occur in stable mixed species flocks and have been widely documented. Sentinel species may be pivotal in 1) allowing flocking species to forage in open areas within forests that otherwise incur high predation risk and 2) maintaining flock cohesion.
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To test this, we conducted a short-term removal experiment in an Amazonian lowland rainforest to evaluate if flock habitat use and cohesion was influenced by sentinel presence. Antshrikes (genus Thamnomanes) act as sentinels in Amazonian mixed species flocks by providing alarm calls widely used by other flock members [13]. The alarm calls provide threat information about ambush predators such as hawks and falcons. We quantified the forest vegetation profile used by flocks, percent occurrence of other flocking species, and their foraging heights both before and after removal of antshrikes from flocks.
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We found that when sentinel species were removed, 1) flock members shifted habitat use to risk- averse habitats containing increased vegetation cover, and, 2) flock cohesion decreased. We conclude that eavesdropping on sentinel species may allow other species to safely forage in high-risk habitats, increasing their realized niche which may influence overall biodiversity across a diverse landscape.
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These two graphs represent the territories of two different flocks. In the control flock (a) , the movements within the territory prior to the 'control treatment' are represented by the blue area, and the red represents the movement after the control treatment.
In the removal flock (b), the movements within the territory prior to the removal of the Antshrike is represented by the blue area, and the red represents the movement after the removal of the Antshrike.
In the removal flock (b), the movements within the territory prior to the removal of the Antshrike is represented by the blue area, and the red represents the movement after the removal of the Antshrike.
| martinezetal2018.pdf |