Anatomical Specializations Related to Foraging in the Visual System of a Nocturnal Insectivorous Bird, the Band-Winged Nightjar (Aves: Caprimulgiformes)

Abstract

Nocturnal animals that rely on their visual system for foraging, mating, and navigation usually exhibit specific traits associated with living in scotopic conditions. Most nocturnal birds have several visual specializations, such as enlarged eyes and an increased orbital convergence. However, the actual role of binocular vision in nocturnal foraging is still debated. Nightjars (Aves: Caprimulgidae) are predators that actively pursue and capture flying insects in crepuscular and nocturnal environments, mainly using a conspicuous “sit-and-wait” tactic on which pursuit begins with an insect flying over the bird that sits on the ground. In this study, we describe the visual system of the band-winged nightjar (Systellura longirostris), with emphasis on anatomical features previously described as relevant for nocturnal birds. Orbit convergence, determined by 3D scanning of the skull, was 73.28°. The visual field, determined by ophthalmoscopic reflex, exhibits an area of maximum binocular overlap of 42°, and it is dorsally oriented. The eyes showed a nocturnal-like normalized corneal aperture/axial length index. Retinal ganglion cells (RGCs) were relatively scant, and distributed in an unusual oblique-band pattern, with higher concentrations in the ventrotemporal quadrant. Together, these results indicate that the band-winged nightjar exhibits a retinal specialization associated with the binocular area of their dorsal visual field, a relevant area for pursuit triggering and prey attacks. The RGC distribution observed is unusual among birds, but similar to that of some visually dependent insectivorous bats, suggesting that those features might be convergent in relation to feeding strategies.

Sensory systems in birds: What we have learned from studying sensory specialists

“…edu.au/nuq/jack/book.html). He also described the retina as bifoveate, a feature that the kite shares with diurnal raptors (Fite & Rosenfield-Wessels, 1975;Inzunza et al, 1991;Inzunza, Bravo, & Smith, 1989;Lisney et al, 2013;Wood, 1917) and not owls (Lisney et al, 2012) or other predatory nocturnal birds (Salazar et al, 2019;Wallman & Pettigrew, 1985). Details on retinal structure were never published, so it remains unknown if the letter-winged kite differs in rod: cone ratio or retinal summation from diurnal raptors.…”

“…Some of his unpublished observations support more limited adaptations to nocturnality such as: efficient hunting requires moonlight and reproductive activities are coordinated with the lunar cycle (see http://www.uq.edu.au/nuq/jack/book.html). He also described the retina as bifoveate, a feature that the kite shares with diurnal raptors (Fite & Rosenfield‐Wessels, ; Inzunza et al, ; Inzunza, Bravo, & Smith, ; Lisney et al, ; Wood, ) and not owls (Lisney et al, ) or other predatory nocturnal birds (Salazar et al, ; Wallman & Pettigrew, ). Details on retinal structure were never published, so it remains unknown if the letter‐winged kite differs in rod: cone ratio or retinal summation from diurnal raptors.…”

Evaluation of the common pauraque (Nyctidromus albicollis) cornea using light and scanning electron microscopy

“…Insectivorous birds generally need high spatial and temporal resolution to successfully capture prey. Caprimulgiformes, however, have the added need for visual specializations that enable successful foraging in scotopic conditions, such as proportionally large eyes positioned to optimize the dorsal visual field, large palpebral openings and high rod‐concentration in the retina (Delaunay et al., 2020; Martin et al., 2004; Moore, Montiani‐Ferreira, & Gardner, 2022; Salazar et al., 2020). Additionally, high visual resolution may benefit detection of predators in addition to their camouflage brown and grey plumage to help remain conspicuous while nesting on the ground among leaves (Guilherme & Lima, 2020; Pérez‐Granados & Schuchmann, 2020; Sandoval & Escalante, 2011; Thurber, 2003).…”

“…Generally, birds have complex visual systems that provide them with excellent visual acuity, and each ocular structure has its specific role in enabling high acuity (Butler et al., 2018; Fernández‐Juricic, 2012; Martin, 2022; Salazar et al., 2020). However, despite being a common and widespread avian species, there is still much to learn about pauraque vision and ecology (Guilherme & Lima, 2020; Pérez‐Granados & Schuchmann, 2020; Thurber, 2003).…”

“…field, large palpebral openings and high rod-concentration in the retina (Delaunay et al, 2020;Martin et al, 2004;Moore, Montiani-Ferreira, & Gardner, 2022;Salazar et al, 2020). Additionally, high visual resolution may benefit detection of predators in addition to their camouflage brown and grey plumage to help remain conspicuous while nesting on the ground among leaves (Guilherme & Lima, 2020;Pérez-Granados & Schuchmann, 2020;Sandoval & Escalante, 2011;Thurber, 2003).…”