Retinal topography in two species of flamingo (Phoenicopteriformes: Phoenicopteridae)

Abstract

In this study, we assessed eye morphology and retinal topography in two flamingo species, the Caribbean flamingo (Phoenicopterus ruber) and the Chilean flamingo (P. chilensis). Eye morphology is similar in both species and cornea size relative to eye size (C:A ratio) is intermediate between those previously reported for diurnal and nocturnal birds. Using stereology and retinal whole mounts, we estimate that the total number of Nissl-stained neurons in the retinal ganglion cell (RGC) layer in the Caribbean and Chilean flamingo is~1.70 and 1.38 million, respectively. Both species have a well-defined visual streak with a peak neuron density of between 13,000 and 16,000 cells mm −2 located in a small central area. Neurons in the high-density regions are smaller and more homogeneous compared to those in medium-and low-density regions. Peak anatomical spatial resolving power in both species is approximately 10-11 cycles/deg. En-face images of the fundus in live Caribbean flamingos acquired using spectral domain optical coherence tomography (SD-OCT) revealed a thin, dark band running nasotemporally just dorsal to the pecten, which aligned with the visual streak in the retinal topography maps. Cross-sectional images (B-scans) obtained with SD-OCT showed that this dark band corresponds with an area of retinal thickening compared to adjacent areas. Neither the retinal whole mounts, nor the SD-OCT imaging revealed any evidence of a central fovea in either species. Overall, we suggest that eye morphology and retinal topography in flamingos reflects their cathemeral activity pattern and the physical nature of the habitats in which they live.

What influences aggression and foraging activity in social birds? Measuring individual, group and environmental characteristics

“…Both wild (Beauchamp & McNeil, 2003;Britton et al, 1986;Tindle, Tupiza, Blomberg, & Tindle, 2014) and captive (Rose, Lloyd, Brereton, & Croft, 2018) flamingos will forage extensively at night, and studies of lesser flamingos across a range of the Rift Valley Lakes document different forms of foraging behaviour at night compared to that observed during daylight hours (Robinson, 2015). The eye of the flamingo has evolved for a cathemeral lifestyle, enabling birds to see in low light levels (Lisney et al, 2020). Consequently, nocturnal foraging may be employed by less successful daytime foragers to make up energy requirement; this hypothesis is supported by observations on wild flamingos that document small groups and single birds foraging overnight (Beauchamp & McNeil, 2003).…”

Retinal Ganglion Cell Topography and Spatial Resolution in Three Indian Pteropodid Bats

“…Retinal ganglion cell (RGC) density maps have been used to estimate visual spatial resolution of a wide range of terrestrial vertebrates including birds (e.g., Wathey and Pettigrew, 1989;Hart, 2002;Coimbra et al, 2012;Mitkus et al, 2014;Lisney et al, 2020), reptiles (e.g., Hart et al, 2012;Hauzman et al, 2014), and mammals (e.g., Coimbra et al, 2013;Coimbra et al, 2017a;Coimbra et al, 2019). Spatial resolution has been estimated from RGC density in more than 25 bat species including 12 pteropodids (online Suppl.…”