Visual acuity and eye size in five European bat species in relation to foraging and migration strategies

Abstract

Optomotor response tests provided visual acuity thresholds in five species of north European insectivorous bats of the family Vespertilionidae. Individuals of three species of predominantly aerial-hawking and trawling Myotis (M. brandtii, M. mystacinus and M. daubentonii) responded only to a stripe pattern equivalent to 5 degrees of arc, whereas the long-distance migrant Pipistrellus nathusii, another aerial-hawking species, responded to 1 degree. In contrast, Plecotus auritus, which is a gleaner and capable of detecting prey using vision alone, responded to a pattern equivalent to 0.5 degrees. The visual acuity was positively correlated with eye diameter, which varied from 0.9 mm in M. mystacinus to 1.7 mm in P. auritus. The results are consistent with earlier findings on related species in other parts of the world. The variation in eye size and visual acuity among insectivorous bats reflect differences in foraging techniques and perhaps also in migrating behavior, thus illustrating how vision is used as a complement to ultrasonic echolocation in various navigation and foraging situations.