A pioneering experiment conducted on coral reefs has unveiled the first-ever evidence of predators using other animals for motion camouflage to stealthily approach their prey without detection. The study, led by the University of Cambridge and involving collaborators from the University of Bristol, focuses on the trumpetfish (Aulostomus maculatus), demonstrating its ability to conceal itself by closely trailing another fish, such as parrotfish, as a form of camouflage while hunting.
In the shadowing behaviour observed, the slender trumpetfish utilizes a non-threatening species, like parrotfish, to mask its presence and get closer to potential prey. This phenomenon marks the only known example of one non-human animal using another for concealment.
The research involved extensive diving in the Caribbean Sea, employing hand-painted model fish drawn along wires. The team discovered that when a trumpetfish moved alongside another fish species, it either remained entirely hidden from its prey or was seen but not recognized as a threat due to the different shape.
The study specifically focused on damselfish (Stegastes partitus), common prey for trumpetfish. By simulating trumpetfish movement using 3D-printed models pulled along lines past damselfish colonies, the researchers observed distinct responses. Damselfish inspected and rapidly fled when the trumpetfish model moved alone, while they responded far less when a model of a herbivorous parrotfish moved alone.
Remarkably, when a trumpetfish model was attached to the side of a parrotfish model to mimic the shadowing behaviour, damselfish responded similarly to when only the parrotfish model was present, indicating a lack of detection of the predatory threat.
Dr. Sam Matchette, the lead researcher at the University of Cambridge, noted, “I was surprised that the damselfish had such a profoundly different response to the different fish; it was great to watch this happening in real time.”
The researchers suggest that this shadowing behavior may be a useful strategy for trumpetfish to enhance hunting success, particularly as coral reefs worldwide face degradation due to climate change, pollution, and overfishing. As structural complexity decreases on reefs, the adaptation of hiding behind other moving fish may become more common.
Dr. James Herbert-Read, senior author of the study at the University of Cambridge, highlighted the potential significance of this behavior in adapting to environmental changes. Drawing parallels to historical human tactics, he mentioned how duck hunters used cardboard cut-outs of domestic animals, known as ‘stalking horses,’ to approach ducks without detection.
The research, funded by The Whitten Programme in Tropical and Aquatic Biology, The Association for the Study of Animal Behavior, and The Fisheries Society of the British Isles, is published in the journal Current Biology.