“Escape distance in ground-nesting birds differs with individual level of camouflage”

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Jared K. Wilson-Aggarwal, Jolyon T. Troscianko, Martin Stevens, and Claire N. Spottiswoode

When predators approach, birds with better egg or plumage camouflage stay with their eggs longer

Birds judge camouflage in the decision of when to flee from a predator

Bronze-winged courser (Rhinoptilus chalcopterus) eggs.
(Credit: Jolyon Troscianko and Project Nightjar)

Researchers from the University of Exeter and the University of Cambridge have revealed that ground-nesting birds can use the camouflage of their eggs or that of their own plumage to decide when to flee from an approaching predator. Camouflage is essential if animals are to avoid being eaten, but the effectiveness of camouflage changes depending on where in the environment an animal chooses to rest. When camouflage is less effective, an animal is at increased risk of being eaten, and may therefore behave differently.

The research shows that birds that have large escape distances (such as plovers and coursers) generally stay on their nest for longer when the pattern of their eggs is a better match to the background. In contrast, animals that have short escape distances (such as nightjars) typically stay on the nest longer when the color and pattern of their own plumage, rather than that of their eggs, is a better match to the background.

Pennant-winged nightjar (Macrodipteryx vexillarius) eggs.
(Credit: Jolyon Troscianko and Project Nightjar)

For plovers and coursers, escape distances are also shortest at midday. This suggests that camouflage is able to mitigate not only predation risk but also thermal risks, by permitting adults to shade their eggs for longer when the risk of overheating is highest.

In Zambia, skilled local assistants helped the researchers find the nests of several species of ground-nesting bird. Once a nest was found, the researchers monitored its progress, recording the escape distance of the adult bird each time they approached and, using camera traps, identified key predators such as the banded mongoose, vervet monkey, and bush shrike. The team also photographed the adult birds and eggs using specially calibrated digital cameras. Sophisticated computer models of animal vision were used to map images to each predator’s visual abilities; from the high color sensitivity of birds that can see ultraviolet wavelengths, to the poor color vision of the banded mongoose that can only see blues and yellows.

The research highlights the important interplay between camouflage and behavior whereby camouflage can help optimize behavioral decisions. Read the Article