Predator Detection is Limited in Microhabitats with High Light Intensity: An Experiment with Brown‐Headed Cowbirds

Abstract

Variations in ambient light conditions across different microhabitats can modify the detectability of predators and prey. Prey have been shown to be more visible in sunlit than in shaded patches, leading to higher predation risk and more investment in vigilance (predation risk hypothesis). Additionally, prey have been hypothesized to take longer to detect predators in sunlit compared to shaded patches because of the excess of sunlight causing glare effects (disability glare hypothesis). We tested the predictions of these two non‐mutually exclusive hypotheses in a seminatural experiment with brown‐headed cowbirds by measuring vigilance behavior and detection of a ground predator in patches under the shade of vegetation and in the open. Light intensity and achromatic contrast were higher in the sunlit patches, which could enhance glare effects, but chromatic contrast was higher in the shaded patches. Brown‐headed cowbirds took longer to show alert reactions to and flee from a ground predator in sunlit compared to shaded patches. However, the two parameters associated with perceived predation risk (vigilance prior to the predator exposure and time to resume foraging after the attack) did not differ between sunlit and shaded patches. Our findings support to a greater extent the disability glare hypothesis than the predation risk hypothesis. Overall, ambient light conditions can affect two critical components of behavioral predator–prey interactions in terrestrial habitats: detection of and escape from predators. The effects of disability glare are expected to be more pronounced in bird species with wider visual fields or without sun‐shading structures; however, species may compensate through various behaviors (e.g. avoidance of sunlit patches and changes in head orientation).

The effects of radar on avian behavior: Implications for wildlife management at airports

“…To encourage foraging behavior, we deprived birds of food from 12 to 20 hr before the trials (following Fernández-Juricic et al, 2012). Prior to each trial, we scattered 5 g of white millet on to the substrate to provide foraging material.…”

Foraging Patch Selection in Winter: A Balance between Predation Risk and Thermoregulation Benefit

“…Contrary to our expectations, we found no effect of illumination determining the time that a forest patch is exploited. This contrast with some studies that relate luminance with both the risk of being detected by a predator and the difficulties the glare poses to detect predators [7],[8],[9],[38].…”

“…The risk of being predated may be related to multiple factors, among which the best known is the distance to a potential refuge against predators [2],[3],[4],[5],[6]. However, there are other factors determining predation risk; for instance, illumination levels highly influence the probabilities of being seen by a potential predator as well as the probabilities of detecting that predator in the surroundings [7],[8],[9].…”

White Sharks Exploit the Sun during Predatory Approaches

“…When the sun strikes their retina, it results in an excess of sunlight in the eye chamber, which reduces retinal image contrast and visual resolution. Such an effect has been referred to as disability glare (Koch 1989;Martin and Katzir 2001) and has been proposed to explain why prey can take longer to detect predators in sunlit compared with shaded areas (Fernández-Juricic et al 2012). Moreover, if the sun is close to or behind the prey, then the sun directly interferes with the prey image.…”