Abstract
Combining studies of animal visual systems with exact imaging of their visual environment can get us a step closer to understand how animals see their “Umwelt”. Here, we have combined both methods to better understand how males of the speckled wood butterfly, Pararge aegeria, see the surroundings of their perches. These males are well known to sit and wait for a chance to mate with a passing females, in sunspot territories in European forests. We provide a detailed description of the males' body and head posture, viewing direction, visual field and spatial resolution, as well as the visual environment. Pararge aegeria has sexually dimorphic eyes, the smallest interommatidial angles of males are around 1°, those of females 1.5°. Perching males face the antisolar direction with their retinal region of the highest resolution pointing at an angle of about 45° above the horizon; thus, looking at a rather even and dark background in front of which they likely have the best chance to detect a sunlit female passing through the sunspot.
Highlights
Mating success strongly depends on the probability of encountering a suitable mate, and mate location strategies vary widely among animals (Thornhill and Alcock 1983)
The importance of the light environment in forest has been pointed out a long time ago (Endler 1993) methods allowing a detailed description have been scarce, the method described by Nilsson and Smolka (2021) being especially promising
Between 10 h and 17.30 h local time, we identified sunspots that were used as perching sites by male P. aegeria in the field
Summary
Mating success strongly depends on the probability of encountering a suitable mate, and mate location strategies vary widely among animals (Thornhill and Alcock 1983). It can be hypothesized that males choose these locations for perching because they increase their chances to mate with a female This advantage could be due to several reasons. Perching butterfly males detect females visually (Bergman and Wiklund 2009); selection should favour males that establish perching sites where females are likely to be encountered, and seen (Rutowski 1991). How a male can detect a female from his perching site, should strongly depend on the contrast between the female and the background. This dependency has only been investigated for one species of perching butterflies, Asterocampa leilia (Bergman et al 2015). The importance of the light environment in forest has been pointed out a long time ago (Endler 1993) methods allowing a detailed description have been scarce, the method described by Nilsson and Smolka (2021) being especially promising
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