Visual fields are repeatable at the population and individual level

Abstract

Avian visual fields have been predicted to be highly conserved at the intraspecific level and be repeatable within an individual, yet this has never been previously determined empirically. Typically, only 2–3 individuals of a species are measured during visual field procedures, and these individuals are measured just once. Using the ophthalmoscopic technique, we measured the visual fields of five Homing Pigeons (Columba livia) over time to assess the repeatability at both the individual and population levels. Using a series of repeatability estimates, we found that visual field measurements were highly repeatable at the individual level, and moderately repeatable at the population levels; visual fields are statistically consistently similar between individuals of the same species and over repeated measures of the same individual. We conclude the ophthalmoscopic technique is a repeatable measure of the visual fields of an individual, and small numbers of individuals are moderately representative of the species. Still, caution should be applied when looking at certain elevations, and higher sample sizes should be used when and where available.