Like many other nocturnal animals, barn owls are believed to have a visual system capable of exploiting their dim surroundings by maximizing sensitivity to small amounts of light by sacrificing fine spatial resolution (Martin,
1986; Warrant,
2004). Barn owls have a rod-dominated retina that lacks an anatomically visible fovea (Fite & Rosenfield-Wessels,
1975; Oehme,
1961). Their fovea displays only a weakly developed horizontal streak of higher ganglion cell density (Wathey & Pettigrew,
1989). The owls' tubular shaped eye has a length of 17.5 mm and an f-number of 1.13. These anatomical features allow for bright retinal images (Schaeffel & Wagner,
1996). The retinal organization in barn owls is indeed typical for night active birds (Jones, Pierce, & Ward,
2007). At high light levels acuity and contrast sensitivity are comparably poor in the owl (Ghim & Hodos,
2006; Harmening, Nikolay, Orlowski, & Wagner,
2009). This is consistent with the retinal sampling limit inferred from ganglion cell density (Wathey & Pettigrew,
1989). The low acuity is in stark contrast to the optical quality of barn owl eyes, which was found to be exceptionally good (Harmening, Vobig, Walter, & Wagner,
2007). High quality optics like those of barn owls are usually conjunct with high-resolution visual systems, as in humans or diurnal raptors (Liang & Williams,
1997; Reymond,
1985). On the other hand, eyes with low aberration produce less deterioration, such as glare, halos, and general blur, and increase image contrast when only little light is available (Huxlin, Yoon, Nagy, Porter, & Williams,
2004). Retinal image quality may thus benefit from good optics also at low spatial frequencies, but it is unclear how much this affects the barn owls' perceptual capabilities, especially at the light levels they usually encounter.