Ambient light in domed nests and discrimination of foreign egg colors

摘要

In cuckoo-host coevolution, rejection of parasite eggs based on visual discrimination is the key host-defensive mechanism reducing the costs of parasitism. Although host discriminatory tasks often occur in variable environmental conditions, the influence of nest light variation on the perceptual processes involved in egg discrimination has been seldom considered. Here, we combine visual modeling, experimental manipulation of nest ambient light, and egg recognition experiments with model eggs differing in background color (cream vs. blue) to explore the possibility that variation in ambient light in magpie (Pica pica) domed nests may affect the perceptual process involved in discrimination of foreign eggs. We found that the architecture of magpie nests affects the quality of ambient light for egg recognition and that changes in luminosity did not differently affect rejection of blue and cream models. However, we found that ejection of model eggs declined throughout the season in nests in which luminosity remained unmodified, but that magpies rejected eggs at a similar rate over the season in nests in which luminosity was increased. These results therefore suggest that variation in ambient light at the nests might potentially influence the perceptual processes involved in visual detection of parasite eggs by cuckoo hosts.