Inter-individual differences in foveal shape in a scavenging raptor, the black kite Milvus migrans

Simon Potier,David Schikorski,Marielle Mentek,Thomas Dulaurent,Almut Kelber,Thomas J Lisney,Thomas J Lisney,Thomas J Lisney,Thomas J Lisney,Thomas J Lisney,Pierre-François Isard,Raphaël Cornette,Raphaël Cornette,Raphaël Cornette,Raphaël Cornette,Mindaugas Mitkus,Mindaugas Mitkus

doi:10.1038/s41598-020-63039-y

Abstract

Birds, and especially raptors, are believed to forage mainly using visual cues. Indeed, raptors (scavengers and predators) have the highest visual acuity known to date. However, scavengers and predators differ in their visual systems such as in their foveal configuration. While the function of the foveal shape remains unknown, individual variation has never been quantified in birds. In this study, we examined whether foveal shape differs among individuals in relation to eye size, sex, age, eye (left or right) and genetic proximity in a scavenging raptor, the black kite Milvus migrans. We assessed foveal shape in 47 individuals using spectral domain optical coherence tomography (OCT) and geometric morphometric analysis. We found that foveal depth was significantly related to eye size. While foveal width also increased with eye size, it was strongly related to age; younger individuals had a wider fovea with a more pronounced rim. We found no relationship between foveal shape and genetic proximity, suggesting that foveal shape is not a hereditary trait. Our study revealed that the shape of the fovea is directly linked to eye size and that the physical structure of the fovea may develop during the entire life of black kites.

Highlights

IntroductionEspecially raptors, are believed to forage mainly using visual cues. raptors (scavengers and predators) have the highest visual acuity known to date
Birds, and especially raptors, are believed to forage mainly using visual cues
While measurements of parameters such as foveal width and depth allowed us to estimate the exact size of the fovea, morphometrics add a new understanding of the shape variation

Summary

Introduction

Especially raptors, are believed to forage mainly using visual cues. raptors (scavengers and predators) have the highest visual acuity known to date. It has been shown that the majority of predatory species such as hawks and eagles have a second fovea placed temporally which is thought to be used for prey fixation at the moment of capture, while raptors that rely more heavily on scavenging, such as vultures and condors, lack this second fovea and instead possess an area of high photoreceptor and ganglion cells density called an area temporalis[11,12,13] In general it is still unclear whether foveae with different shapes have functional differences. In the “normal” population of humans, the foveal shape is highly variable[24]

Methods

Discussion

Conclusion