scholarly journals Visual Adaptations in Predatory and Scavenging Diurnal Raptors

Diversity ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 400
Author(s):  
Simon Potier
Keyword(s):  
Prey Capture ◽  
Foraging Ecology ◽  
Visual Fields ◽  
Blind Spot ◽  
Field Of View ◽  
Birds Of Prey ◽  
Ecological Diversity ◽  
Complex Interplay ◽  
Visual Systems ◽  
Central Fovea

Ecological diversity among diurnal birds of prey, or raptors, is highlighted regarding their sensory abilities. While raptors are believed to forage primarily using sight, the sensory demands of scavengers and predators differ, as reflected in their visual systems. Here, I have reviewed the visual specialisations of predatory and scavenging diurnal raptors, focusing on (1) the anatomy of the eye and (2) the use of vision in foraging. Predators have larger eyes than scavengers relative to their body mass, potentially highlighting the higher importance of vision in these species. Scavengers possess one centrally positioned fovea that allows for the detection of carrion at a distance. In addition to the central fovea, predators have a second, temporally positioned fovea that views the frontal visual field, possibly for prey capture. Spatial resolution does not differ between predators and scavengers. In contrast, the organisation of the visual fields reflects important divergences, with enhanced binocularity in predators opposed to an enlarged field of view in scavengers. Predators also have a larger blind spot above the head. The diversity of visual system specializations according to the foraging ecology displayed by these birds suggests a complex interplay between visual anatomy and ecology, often unrelatedly of phylogeny.

Raptor Vision

2018 ◽  
Author(s):  
Mindaugas Mitkus ◽  
Simon Potier ◽  
Graham R. Martin ◽  
Olivier Duriez ◽  
Almut Kelber
Keyword(s):  
Visual Acuity ◽  
Visual Fields ◽  
Field Of View ◽  
Visual Performance ◽  
Low Density ◽  
Prey Detection ◽  
Light Levels ◽  
Extensive Field ◽  
Visual Properties ◽  
Central Fovea

Diurnal raptors (birds of the orders Accipitriformes and Falconiformes), renowned for their extraordinarily sharp eyesight, have fascinated humans for centuries. The high visual acuity in some raptor species is possible due to their large eyes, both in relative and absolute terms, and a high density of cone photoreceptors. Some large raptors, such as wedge-tailed eagles and the Old World vultures, have visual acuities twice as high as humans and six times as high as ostriches—the animals with the largest terrestrial eyes. The raptor retina has rods, double cones, and four spectral types of single cones. The highest density of single cones occurs in one or two specialized retinal regions: the foveae, where, at least in some species, rods and double cones are absent. The deep central fovea allows for the highest acuity in the lateral visual field that is probably used for detecting prey from a large distance. Pursuit-hunting raptors have a second, shallower, temporal fovea that allows for sharp vision in the frontal field of view. Scavenging carrion eaters do not possess a temporal fovea that may indicate different needs in foraging behavior. Moreover, pursuit-hunting and scavenging raptors also differ in configuration of visual fields, with a more extensive field of view in scavengers. The eyes of diurnal raptors, unlike those of most other birds, are not very sensitive to ultraviolet light, which is strongly absorbed by their cornea and lens. As a result of the low density of rods, and the narrow and densely packed single cones in the central fovea, the visual performance of diurnal raptors drops dramatically as light levels decrease. These and other visual properties underpin prey detection and pursuit and show how these birds’ vision is adapted to make them successful diurnal predators.

External Design and Field of View of the Compound Eyes in a Raptorial Neuropteran Insect, Mantispa Styriaca

1990 ◽  
Vol 148 (1) ◽  
pp. 353-365 ◽  
Author(s):  
U. EGGENREICH ◽  
K. KRAL
Keyword(s):  
Dark Adaptation ◽  
Visual Fields ◽  
Field Of View ◽  
Compound Eyes ◽  
Praying Mantis ◽  
Binocular Field ◽  
Frontal Part

Visual fields and ommatidial angles of the compound eyes of Mantispa styriaca were determined using luminous pseudopupil and histological-anatomical techniques. The maximal horizontal overlap averaged 42.7° in femalesand 52.4° in males; females had only one overlap maximum, whereas males had two. In the dorsoventral direction, the binocular field had an overlap of 135.2° in the female and 142° in the male. In light-adapted eyes, optical acceptance angles reached values of 2.0°, and they reached 3.6° with dark adaptation; interommatidial angles were between 1.8° and 2.3°. The angles were very similar over the entire eye; no acute zone was found in the frontal part of the eye, as the large binocular overlap would suggest. The results are compared with those for the praying mantis: this animal is in no way related to Mantispa but resembles it in appearance and capture behaviour.

Foraging ecology of the horseshoe bat, Rhinolophus megaphyllus (Rhinolophidae), in eastern Australia

2004 ◽  
Vol 31 (4) ◽  
pp. 403 ◽  
Author(s):  
Chris R. Pavey ◽  
Chris J. Burwell
Keyword(s):  
Prey Capture ◽  
Foraging Ecology ◽  
Light Trap ◽  
Foraging Strategy ◽  
Flying Insects ◽  
Open Forest ◽  
Eastern Australia ◽  
Wide Range ◽  
Horseshoe Bat ◽  
Conservation Concern

The foraging ecology of the eastern horseshoe bat, Rhinolophus megaphyllus, was examined at five sites spread along 2100 km of its Australian distribution in coastal Queensland. Foraging strategy and prey-capture behaviour of light-tagged bats were similar across sites. Bats were observed foraging during continuous flight at all sites, whereas perch hunting was observed (rarely) at only one site. Bats captured insects by aerial hawking, with a single record of gleaning. In rainforest bats spent most time close to vegetation whereas openings were favoured in open forest/woodland. Only flying insects were captured and, although a wide range of taxa was taken, Lepidoptera (all sites) and Coleoptera (all sites except one) were the primary prey. Occurrence in faeces of Lepidoptera, Coleoptera, and other taxa combined, varied across sites and across seasons, but there was no three-way interaction between taxon, site and season. Comparison of insect taxa in faeces with those captured in a light-trap set at foraging grounds indicated that insects were selectively captured by R. megaphyllus. The foraging ecology of R. megaphyllus is similar to that of other horseshoe bats in its relative stability across a large geographic range. Although the species is currently not of conservation concern in Australia, aspects of its foraging ecology suggest that it may become regionally threatened in areas with high levels of vegetation clearance.

Behavioral evidence of filling-in at the blind spot of the monkey

1994 ◽  
Vol 11 (6) ◽  
pp. 1103-1113 ◽  
Author(s):  
Hidehiko Komatsu ◽  
Ikuya Murakami
Keyword(s):  
Visual Field ◽  
Human Subjects ◽  
Visual Fields ◽  
Blind Spot ◽  
Neural Mechanisms ◽  
Opposite Field ◽  
Normal Visual Field ◽  
Saccade Task ◽  
Behavioral Evidence ◽  
Blind Spots

AbstractIn human subjects, the blind spot is perceptually filled-in by color and brightness from the surrounding visual field. The present behavioral study examined the occurrence of color filling-in at the blind spot in monkeys. First, the location of the blind spot was determined using a monocular saccade task. The blind spots were located on the horizontal meridian at approximately 15–17 deg from the fixation point in the temporal visual field. Then, filling-in at the blind spot was tested by determining if the monkey could discriminate between an annulus presented on the blind spot and a homogeneous disk in the normal visual field. In this task, the monkey was required to make a saccade to a homogeneous disk of the same color and size as an annulus presented simultaneously in the opposite field. Both stimuli were large enough to cover the blind spot and the inner circle of the annulus was confined inside the blind spot. All four monkeys tested performed this task correctly in over 80% of the trials. However, when one eye was covered and the annulus was presented on the blind spot of the uncovered eye, performance deteriorated significantly. To confirm that these results reflected filling-in, one monkey was trained to maintain fixation when two identical homogeneous disks appeared in opposite visual fields. When only one eye was uncovered, and the annulus was presented on the blind spot of the uncovered eye, the monkey maintained fixation in most of the trials. These results show that monkeys were unable to distinguish an annulus from a homogeneous disk when the annulus was presented on the blind spot. This indicates that color filling-in occurs at the blind spot in monkeys and opens possibility to physiological experiments to study the neural mechanisms of filling-in.

scholarly journals Visual fields and foraging ecology of Blacksmith Lapwings Vanellus armatus

Ibis ◽  
2019 ◽  
Vol 161 (4) ◽  
pp. 895-900
Author(s):  
Jennifer C. Cantlay ◽  
Steven J. Portugal ◽  
Graham R. Martin
Keyword(s):  
Foraging Ecology ◽  
Visual Fields

The visual fields of American horseshoe crabs: Two different eye shapes in Limulus polyphemus

1994 ◽  
Vol 11 (2) ◽  
pp. 333-346 ◽  
Author(s):  
William W. Weiner ◽  
Steven C. Chamberlain
Keyword(s):  
Adult Male ◽  
Visual Fields ◽  
Vertical Axis ◽  
Limulus Polyphemus ◽  
Field Of View ◽  
Male And Female ◽  
Maximum Resolution ◽  
Lateral Eye ◽  
Horseshoe Crabs ◽  
Optical Alignment

AbstractThe optical alignment of individual cuticular cones in the dioptric array of the lateral eye of Limulus polyphemus was determined with a precision two-circle goniometer constructed and mounted to the stage of a compound microscope and using a new formaldehyde-induced fluorescence procedure. All measurements were made from the corneal surface of the excised eye mounted in seawater through an air/water interface perpendicular to the optic axis of the microscope. Our results revealed two variants of visual field and eye curvature which can actually be discriminated in casual examination of adult animals. We call animals possessing these two variants “morlocks” and “eloi.” Adult male and female morlocks about 25 cm across the carapace have eyes which are relatively elongated, often darker in pigmentation, smaller, and relatively flatter in curvature. Morlocks have a monocular field of view of about 3.13 steradians or 50% of a hemisphere. The coverage averages 115 deg along the vertical axis and 168 deg along the horizontal axis of the eye, with maximum resolution in the anteroventral quadrant. Adult male and female eloi of comparable size have eyes which are relatively more round, often lighter in pigmentation, larger with more ommatidia, and relatively more bulged. Eloi have a monocular field of view of approximately 3.83 steradians or 61% of a hemisphere that covers 145 deg vertically and 185 deg horizontally. Eloi have more uniform resolution than morlocks with best resolution in the posteroventral quadrant. All horseshoe crabs examined, whether morlocks or eloi, have an identical orientation of the margin of the eye relative to the animals’ coordinates.

Hybrid Dual Camera Vision Systems

2011 ◽  
pp. 848-852
Author(s):  
Stefano Cagnoni ◽  
Monica Mordonini ◽  
Luca Mussi ◽  
Giovanni Adorni
Keyword(s):  
Mobile Robotics ◽  
Three Dimensional ◽  
Research Field ◽  
Field Of View ◽  
Wide Field ◽  
Vision Systems ◽  
Visual Systems ◽  
Field Of Vision ◽  
Wide Field Of View ◽  
Critical Requirement

Many of the known visual systems in nature are characterized by a wide field of view allowing animals to keep the whole surrounding environment under control. In this sense, dragonflies are one of the best examples: their compound eyes are made up of thousands of separate light-sensing organs arranged to give nearly a 360° field of vision. However, animals with eyes on the sides of their head have high periscopy but low binocularity, that is their views overlap very little. Differently, raptors’ eyes have a central part that permits them to see far away details with an impressive resolution and their views overlap by about ninety degrees. Those characteristics allow for a globally wide field of view and for accurate stereoscopic vision at the same time, which in turn allows for determination of distance, leading to the ability to develop a sharp, three-dimensional image of a large portion of their view. In mobile robotics applications, autonomous robots are required to react to visual stimuli that may come from any direction at any moment of their activity. In surveillance applications, the opportunity to obtain a field of view as wide as possible is also a critical requirement. For these reasons, a growing interest in omnidirectional vision systems (Benosman 2001), which is still a particularly intriguing research field, has emerged. On the other hand, requirements to be able to carry out object/pattern recognition and classification tasks are opposite, high resolution and accuracy and low distortion being possibly the most important ones. Finally, three-dimensional information extraction can be usually achieved by vision systems that combine the use of at least two sensors at the same time. This article presents the class of hybrid dual camera vision systems. This kind of sensors, inspired by existing visual systems in nature, combines an omnidirectional sensor with a perspective moving camera. In this way it is possible to observe the whole surrounding scene at low resolution, while, at the same time, the perspective camera can be directed to focus on objects of interest with higher resolution.

The foraging ecology of the gray rat snake (Elaphe obsoleta spiloides). III. Searching for different prey types in structurally varied habitats

1998 ◽  
Vol 76 (3) ◽  
pp. 548-555 ◽  
Author(s):  
Stephen J Mullin ◽  
Robert J Cooper ◽  
William HN Gutzke
Keyword(s):  
Prey Capture ◽  
Foraging Ecology ◽  
Structural Complexity ◽  
Prey Type ◽  
Foraging Strategies ◽  
Vegetation Density ◽  
Small Rodents ◽  
Elaphe Obsoleta ◽  
Rat Snake ◽  
Low Levels

Dietary generalists foraging for prey inhabiting different microhabitats may encounter different levels of structural complexity. We examined the effect of variation in prey type on the predation success and behaviors of the semi-arboreal gray rat snake (Elaphe obsoleta spiloides) foraging in structurally varied habitats. Individual snakes searched for contents of arboreal birds' nests or for small rodents in enclosures that simulated a bottomland hardwood forest habitat with one of five levels of vegetation density. Latency to prey capture was lower when the snakes were searching for small rodents than when they were searching for birds' nests, and lower for male snakes than for females. Generally, snakes were most successful when searching for prey in enclosures with low levels of structural complexity, and experienced decreased predation success in barren or highly complex habitats. Habitats with low levels of structural complexity may offer the snakes concealment from predation while not obscuring their perception or pursuit of prey. Of behavior durations measured in the trials, over 95% concerned 6 of the 20 behaviors described, and 3 of these occurred more often than the others, regardless of variation in the structural complexity of the habitat. Foraging gray rat snakes exhibited behaviors characteristic of active and ambush foraging strategies that increased their predation success on different prey types in the varied environments.

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