Habitat Change and Timing of Dusk Flight in the Eurasian Woodcock: A Trade-Off between Feeding and Predator Avoidance?

Abstract

Braña, F., Prieto, L. & González-Quirós, P. 2010: Habitat change and timing of dusk flight in the Eurasian woodcock: a trade-off between feeding and predator avoidance? -Ann. Eurasian woodcock (Scolopax rusticola) over-wintering in northern Spain follows a pattern of daily movement from diurnal sites in woodlands to nighttime sites in grazed fields, congruent with previous reports on other European populations. Fields have a much higher abundance and biomass of earthworms, the main prey of woodcock, than woodlands, but are only used by birds at night, when they emerge about 30 minutes after sunset. Emergence time was quite uniform among fortnightly periods except for the second half of November when it was earlier, probably reflecting extended activity resulting from the higher energy requirements of migrating birds. Woodcock emergence time relative to sunset was negatively related to illumination, so that birds moved earlier when the sky was overcast. Also, birds tended to move earlier at low air temperatures, a pattern which is to be predicted since woodcock have higher energy requirements at low temperatures because of the increased cost of thermoregulation. Emerging late, at low light intensity, avoids exposure to raptors but results in reduced energy gains and therefore the timing of moving to feeding fields may be modified by energy considerations. We discuss the idea that there is a divergent spatio-temporal gradient of food and safety between woodlands and fields and, therefore, that predation risk is an important determinant of the timing of evening emergence of over-wintering woodcock. Thus, their daily activity cycle would reflect a trade-off between feeding and predator avoidance. Special features of the visual fields of the woodcock, allowing detection of predators at long distances, and chemoreceptors in the bill enabling detection and capture of prey by probing using non visual cues, comprise adaptations that facilitate successful feeding at night with reduced predation risk.

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

“…Brañ a et al 2010). 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).…”

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].…”

White Sharks Exploit the Sun during Predatory Approaches

“…Past studies have successfully shown that the behavior of prey species can be mediated by light intensity (Fernández-Juricic and Tran 2007;Braña et al 2010) and sun direction (Carr and Lima 2014), with those studies often relating these behavioral changes to the trade-off between feeding and predator avoidance. The few studies that suggested that predators exploit the sun during predation provide poor or ambiguous evidence.…”