The visual fields of vultures contain a small binocular region and large blind areas above, below... more The visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage of the ground below, prohibit the eyes from imaging the sun and provide extensive visual coverage laterally. However, vultures will often be blind in the direction of travel. We conclude that by erecting structures such as wind turbines, which extend into open airspace, humans have provided a ...
Although flight is regarded as a key behavior of birds this review argues that the perceptual dem... more Although flight is regarded as a key behavior of birds this review argues that the perceptual demands for its control are met within constraints set by the perceptual demands of two other key tasks: the control of bill (or feet) position, and the detection of food items/predators. Control of bill position, or of the feet when used in foraging, and timing of their arrival at a target, are based upon information derived from the optic flow-field in the binocular region that encompasses the bill. Flow-fields use information extracted from close to the bird using vision of relatively low spatial resolution. The detection of food items and predators is based upon information detected at a greater distance and depends upon regions in the retina with relatively high spatial resolution. The tasks of detecting predators and of placing the bill (or feet) accurately, make contradictory demands upon vision and these have resulted in trade-offs in the form of visual fields and in the topography of retinal regions in which spatial resolution is enhanced, indicated by foveas, areas, and high ganglion cell densities. The informational function of binocular vision in birds does not lie in binocularity per se (i.e., two eyes receiving slightly different information simultaneously about the same objects) but in the contralateral projection of the visual field of each eye. This ensures that each eye receives information from a symmetrically expanding optic flow-field centered close to the direction of the bill, and from this the crucial information of direction of travel and time-to-contact can be extracted, almost instantaneously. Interspecific comparisons of visual fields between closely related species have shown that small differences in foraging techniques can give rise to different perceptual challenges and these have resulted in differences in visual fields even within the same genus. This suggests that vision is subject to continuing and relatively rapid natural selection based upon individual differences in the structure of the optical system, retinal topography, and eye position in the skull. From a sensory ecology perspective a bird is best characterized as " a bill guided by an eye " and that control of flight is achieved within constraints on visual capacity dictated primarily by the demands of foraging and bill control.
For more information about postage charges and delivery times visit ww.oup.com/academic/help/ship... more For more information about postage charges and delivery times visit ww.oup.com/academic/help/shipping/. *only when you order directly via www.oup.com/academic/, adding promotion code ACFLYP8 to your shopping basket. Discount valid until 30/08/2017. Limit 10 copies per transaction. This offer is only available to individual (non-trade) customers. This offer is exclusive and cannot be redeemed in conjunction with any other promotional discounts. The specifications in this leaflet, including without limitation price, format, extent, number of illustrations, and month of publication, were as accurate as possible at the time it went to press. • The first integrated synthesis of avian sensory ecology • Explains the broad principles and takes the reader into the sensory world of birds from an evolutionary and ecological perspective • Challenges people's assumptions about the sensory worlds of birds and shows how these are tuned to the many perceptual challenges that birds face in their natural environments • Presents insights into the reasons why birds are often victims of collisions with static structures, vehicles and nets, and suggests mitigations
Differences in visual capabilities are known to reflect differences in foraging behaviour even am... more Differences in visual capabilities are known to reflect differences in foraging behaviour even among closely related species. Among birds, the foraging of diurnal raptors is assumed to be guided mainly by vision but their foraging tactics include both scavenging upon immobile prey and the aerial pursuit of highly mobile prey. We studied how visual capabilities differ between two diurnal raptor species of similar size; Harris's Hawks Parabuteo unicinctus, which take mobile prey, and Black Kites Milvus migrans, which are primarily carrion eaters. We measured visual acuity, foveal characteristics and visual fields in both species. Visual acuity was determined using a behavioural training technique; foveal characteristics were determined using ultra-high resolution spectral-domain optical coherence tomography (OCT) and visual field parameters were determined using an ophthalmoscopic reflex technique. We found that these two raptors differ in their visual capacities. Harris's Haw...
Journal of Comparative Physiology a Sensory Neural and Behavioral Physiology, 1985
The photoreceptors of the penguin,Spheniscus humboldti, were examined using a microspectrophotome... more The photoreceptors of the penguin,Spheniscus humboldti, were examined using a microspectrophotometer. The cones could be divided into three classes based on their visual pigment absorbance spectra [?max 403, 450 and 543 nm (Fig. 1)], and into five classes based on their visual pigment-oil droplet combination (Fig. 4). Oil droplets were of three types (Fig. 2). The rods contained a rhodopsin
The Manx shearwater, Puffinus puffinus, is a pelagic sea bird which feeds from the surface of the... more The Manx shearwater, Puffinus puffinus, is a pelagic sea bird which feeds from the surface of the sea and by shallow surface and plunge dives. Visits to breeding colonies are made at night. The mononuclear retinal field of the Manx shearwater eye is 148 degrees wide and is asymmetric with respect to the optic axis. The nasal and temporal hemi-fields equal 65 and 83 degrees, respectively. The binocular field is long and narrow, and the central placement of the bill suggests that vision is used to guide the bill position during foraging. A schematic model of the shearwater eye's optical system is presented, together with reanalysed data on the optical structure in the eye of the pigeon, Columba livia. The eyes of these two species are nearly identical in axial length and overall shape, but they are of quite different optical design. The shearwater eye has a shorter focal length and higher maximum image brightness, and the ratio of corneal:lens refractive power equals 0.4 and 1.6 in pigeon and shearwater eyes, respectively. In Manx shearwater eyes, the ratio of focal length:axial length and the ratio of lens refractive power:corneal refractive power may be correlated with a nocturnal life style. It is not clear whether the relatively low refractive power of the cornea is best regarded as a feature correlated with an amphibious life style or whether it is a consequence of adaptations for nocturnal activity.
Journal of Comparative and Physiological Psychology, 1974
Abstract 1. Trained 4 tawny owls to discriminate simultaneously between blue (437 nm) and green (... more Abstract 1. Trained 4 tawny owls to discriminate simultaneously between blue (437 nm) and green (547 nm) lights and between red (672 nm) and green (547 nm) lights. The relative luminances of the stimulus pairs were randomly varied. This procedure, together with the ...
An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular f... more An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular field width occurs approximately 20 degrees above the bill. The binocular field has a maximum width of 27 degrees and extends vertically by 130 degrees (90 degrees above the bill, 40 degrees below it). Both the bill and cere intrude into the binocular field. Maximum optical binocularity also occurs approximately 20 degrees above the bill. The plane containing the optic axes of each eye coincides with the bill.
The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degre... more The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degrees is less than that recorded in any other vertebrate. Maximum retinal binocular field width equals 48 degrees and the optic axes diverge by 55 degrees. Maximum binocularity occurs above the bill whose tip lies outside of the visual field. The cyclopean retinal field has a maximum width of 201 degrees. Limited data on the visual fields of the pigeon are also presented. All of these data are compared with visual field widths in other species and the significance of the owl eye's tubular shape, its nasad asymmetry, and the possible factors influencing binocular field width are discussed.
Visual field characteristics were measured using an ophthalmoscopic reflex technique in Oil- bird... more Visual field characteristics were measured using an ophthalmoscopic reflex technique in Oil- birds (Steatornis caripensis) and Pauraques (Nyctidromus albicollis). Despite these birds' apparent frontal-eyed appearance, their functional binocular fields are relatively small with a maximum width of 38º and vertical extent of 100º in Oilbirds, and 25º x 110º in Pauraques. Maximum width occurred 10º above the horizontal in both
Sensory capacities and perceptual challenges faced by gillnet bycatch taxa result from fundamenta... more Sensory capacities and perceptual challenges faced by gillnet bycatch taxa result from fundamental physiological limits on vision and constraints arising within underwater environments. To reduce bycatch in birds, sea turtles, pinnipeds and blue-water fishes, individuals must be alerted to the presence of nets using visual cues. Cetaceans will benefit but they also require warning with cues detected through echolocation. Characteristics of a visual warning stimulus must accommodate the restricted visual capacities of bycatch species and the need to maintain vision in a dark adapted state when foraging. These requirements can be provided by a single type of visual warning stimulus: panels containing a pattern of low spatial frequency and high internal contrast. These are likely to be detectable across a range of underwater light environments by all bycatch prone taxa, but are unlikely to reduce the catch of target fish species. Such panels should also be readily detectable by cetaceans using echolocation. Use of sound signals to warn about the presence of gillnets is not recommended because of the poor sound localisation abilities of bycatch taxa, cetaceans excepted. These warning panels should be effective as a mitigation measure for all bycatch species, relatively easy to deploy and of low cost.
Masked boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate ne... more Masked boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate nests. However, their nest sites produce a characteristic 'nest signature'. We found that these nest signatures could apparently be seen in freely available satellite images (Google Earth TM ) of the main island of Ascension in the south Atlantic. We verified that this was the case by comparing nest signatures detected on these satellite images with field reports of occupied nests. We found that the locations of these nest signatures determined from satellite images agreed closely with the coordinates of actual nests on the ground. We used this information to determine the position and size of a previously unreported masked booby colony on the island. Thus, we show that the presence and abundance of some species can be estimated using freely available satellite imagery if a suitable signature in the satellite image can be found. Regularly updated satellite imagery of target sites could also be used for population monitoring. While this would be expensive, initial evaluation of the technique for particular species or populations can be achieved using freely available images. We encourage wildlife managers to view their study sites on Google Earth TM for evidence of their target species.
Threshold visual acuity for grating stimuli was determined in two tawny owls (a totally nocturnal... more Threshold visual acuity for grating stimuli was determined in two tawny owls (a totally nocturnal avian species). Extensive training was given in a runway apparatus in which stimuli were presented well beyond the near point at a distance of 95 cm. Stimuli were presented according to a modified Method of Constant Stimuli. At a stimulus luminance of 1.7 log mL acuity thresholds for the two birds equalled 2.7' and 3.7'. Acuity was also determined in one bird at stimulus luminance of @2 and 1.2 log mL. and equalled 34' and 25' at each luminance respectively. These thresholds are compared with those of two humans tested in the same apparatus and with previously published acuity data for other avian and nocturnal species.
The mallard duck has a retinal visual field giving 360 degrees visual coverage in the horizontal ... more The mallard duck has a retinal visual field giving 360 degrees visual coverage in the horizontal plane and a narrow binocular field of approximately uniform width (approximately equal to 20 degrees) extending through 220 degrees from the bill to directly behind the head. Measurement of the optical fields indicate that the binocular retinal field could be considerably larger than actually found. Eye movements are not of sufficient amplitude to abolish binocularity at any elevation.
The visual fields of vultures contain a small binocular region and large blind areas above, below... more The visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage of the ground below, prohibit the eyes from imaging the sun and provide extensive visual coverage laterally. However, vultures will often be blind in the direction of travel. We conclude that by erecting structures such as wind turbines, which extend into open airspace, humans have provided a ...
Although flight is regarded as a key behavior of birds this review argues that the perceptual dem... more Although flight is regarded as a key behavior of birds this review argues that the perceptual demands for its control are met within constraints set by the perceptual demands of two other key tasks: the control of bill (or feet) position, and the detection of food items/predators. Control of bill position, or of the feet when used in foraging, and timing of their arrival at a target, are based upon information derived from the optic flow-field in the binocular region that encompasses the bill. Flow-fields use information extracted from close to the bird using vision of relatively low spatial resolution. The detection of food items and predators is based upon information detected at a greater distance and depends upon regions in the retina with relatively high spatial resolution. The tasks of detecting predators and of placing the bill (or feet) accurately, make contradictory demands upon vision and these have resulted in trade-offs in the form of visual fields and in the topography of retinal regions in which spatial resolution is enhanced, indicated by foveas, areas, and high ganglion cell densities. The informational function of binocular vision in birds does not lie in binocularity per se (i.e., two eyes receiving slightly different information simultaneously about the same objects) but in the contralateral projection of the visual field of each eye. This ensures that each eye receives information from a symmetrically expanding optic flow-field centered close to the direction of the bill, and from this the crucial information of direction of travel and time-to-contact can be extracted, almost instantaneously. Interspecific comparisons of visual fields between closely related species have shown that small differences in foraging techniques can give rise to different perceptual challenges and these have resulted in differences in visual fields even within the same genus. This suggests that vision is subject to continuing and relatively rapid natural selection based upon individual differences in the structure of the optical system, retinal topography, and eye position in the skull. From a sensory ecology perspective a bird is best characterized as " a bill guided by an eye " and that control of flight is achieved within constraints on visual capacity dictated primarily by the demands of foraging and bill control.
For more information about postage charges and delivery times visit ww.oup.com/academic/help/ship... more For more information about postage charges and delivery times visit ww.oup.com/academic/help/shipping/. *only when you order directly via www.oup.com/academic/, adding promotion code ACFLYP8 to your shopping basket. Discount valid until 30/08/2017. Limit 10 copies per transaction. This offer is only available to individual (non-trade) customers. This offer is exclusive and cannot be redeemed in conjunction with any other promotional discounts. The specifications in this leaflet, including without limitation price, format, extent, number of illustrations, and month of publication, were as accurate as possible at the time it went to press. • The first integrated synthesis of avian sensory ecology • Explains the broad principles and takes the reader into the sensory world of birds from an evolutionary and ecological perspective • Challenges people's assumptions about the sensory worlds of birds and shows how these are tuned to the many perceptual challenges that birds face in their natural environments • Presents insights into the reasons why birds are often victims of collisions with static structures, vehicles and nets, and suggests mitigations
Differences in visual capabilities are known to reflect differences in foraging behaviour even am... more Differences in visual capabilities are known to reflect differences in foraging behaviour even among closely related species. Among birds, the foraging of diurnal raptors is assumed to be guided mainly by vision but their foraging tactics include both scavenging upon immobile prey and the aerial pursuit of highly mobile prey. We studied how visual capabilities differ between two diurnal raptor species of similar size; Harris's Hawks Parabuteo unicinctus, which take mobile prey, and Black Kites Milvus migrans, which are primarily carrion eaters. We measured visual acuity, foveal characteristics and visual fields in both species. Visual acuity was determined using a behavioural training technique; foveal characteristics were determined using ultra-high resolution spectral-domain optical coherence tomography (OCT) and visual field parameters were determined using an ophthalmoscopic reflex technique. We found that these two raptors differ in their visual capacities. Harris's Haw...
Journal of Comparative Physiology a Sensory Neural and Behavioral Physiology, 1985
The photoreceptors of the penguin,Spheniscus humboldti, were examined using a microspectrophotome... more The photoreceptors of the penguin,Spheniscus humboldti, were examined using a microspectrophotometer. The cones could be divided into three classes based on their visual pigment absorbance spectra [?max 403, 450 and 543 nm (Fig. 1)], and into five classes based on their visual pigment-oil droplet combination (Fig. 4). Oil droplets were of three types (Fig. 2). The rods contained a rhodopsin
The Manx shearwater, Puffinus puffinus, is a pelagic sea bird which feeds from the surface of the... more The Manx shearwater, Puffinus puffinus, is a pelagic sea bird which feeds from the surface of the sea and by shallow surface and plunge dives. Visits to breeding colonies are made at night. The mononuclear retinal field of the Manx shearwater eye is 148 degrees wide and is asymmetric with respect to the optic axis. The nasal and temporal hemi-fields equal 65 and 83 degrees, respectively. The binocular field is long and narrow, and the central placement of the bill suggests that vision is used to guide the bill position during foraging. A schematic model of the shearwater eye's optical system is presented, together with reanalysed data on the optical structure in the eye of the pigeon, Columba livia. The eyes of these two species are nearly identical in axial length and overall shape, but they are of quite different optical design. The shearwater eye has a shorter focal length and higher maximum image brightness, and the ratio of corneal:lens refractive power equals 0.4 and 1.6 in pigeon and shearwater eyes, respectively. In Manx shearwater eyes, the ratio of focal length:axial length and the ratio of lens refractive power:corneal refractive power may be correlated with a nocturnal life style. It is not clear whether the relatively low refractive power of the cornea is best regarded as a feature correlated with an amphibious life style or whether it is a consequence of adaptations for nocturnal activity.
Journal of Comparative and Physiological Psychology, 1974
Abstract 1. Trained 4 tawny owls to discriminate simultaneously between blue (437 nm) and green (... more Abstract 1. Trained 4 tawny owls to discriminate simultaneously between blue (437 nm) and green (547 nm) lights and between red (672 nm) and green (547 nm) lights. The relative luminances of the stimulus pairs were randomly varied. This procedure, together with the ...
An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular f... more An ophthalmoscopic reflex technique has shown that in sedated pigeons maximum retinal binocular field width occurs approximately 20 degrees above the bill. The binocular field has a maximum width of 27 degrees and extends vertically by 130 degrees (90 degrees above the bill, 40 degrees below it). Both the bill and cere intrude into the binocular field. Maximum optical binocularity also occurs approximately 20 degrees above the bill. The plane containing the optic axes of each eye coincides with the bill.
The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degre... more The uniocular retinal field of Strix aluco is highly asymmetrical. The maximum width of 124 degrees is less than that recorded in any other vertebrate. Maximum retinal binocular field width equals 48 degrees and the optic axes diverge by 55 degrees. Maximum binocularity occurs above the bill whose tip lies outside of the visual field. The cyclopean retinal field has a maximum width of 201 degrees. Limited data on the visual fields of the pigeon are also presented. All of these data are compared with visual field widths in other species and the significance of the owl eye's tubular shape, its nasad asymmetry, and the possible factors influencing binocular field width are discussed.
Visual field characteristics were measured using an ophthalmoscopic reflex technique in Oil- bird... more Visual field characteristics were measured using an ophthalmoscopic reflex technique in Oil- birds (Steatornis caripensis) and Pauraques (Nyctidromus albicollis). Despite these birds' apparent frontal-eyed appearance, their functional binocular fields are relatively small with a maximum width of 38º and vertical extent of 100º in Oilbirds, and 25º x 110º in Pauraques. Maximum width occurred 10º above the horizontal in both
Sensory capacities and perceptual challenges faced by gillnet bycatch taxa result from fundamenta... more Sensory capacities and perceptual challenges faced by gillnet bycatch taxa result from fundamental physiological limits on vision and constraints arising within underwater environments. To reduce bycatch in birds, sea turtles, pinnipeds and blue-water fishes, individuals must be alerted to the presence of nets using visual cues. Cetaceans will benefit but they also require warning with cues detected through echolocation. Characteristics of a visual warning stimulus must accommodate the restricted visual capacities of bycatch species and the need to maintain vision in a dark adapted state when foraging. These requirements can be provided by a single type of visual warning stimulus: panels containing a pattern of low spatial frequency and high internal contrast. These are likely to be detectable across a range of underwater light environments by all bycatch prone taxa, but are unlikely to reduce the catch of target fish species. Such panels should also be readily detectable by cetaceans using echolocation. Use of sound signals to warn about the presence of gillnets is not recommended because of the poor sound localisation abilities of bycatch taxa, cetaceans excepted. These warning panels should be effective as a mitigation measure for all bycatch species, relatively easy to deploy and of low cost.
Masked boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate ne... more Masked boobies Sula dactylatra, like many other species of Sulidae, do not construct elaborate nests. However, their nest sites produce a characteristic 'nest signature'. We found that these nest signatures could apparently be seen in freely available satellite images (Google Earth TM ) of the main island of Ascension in the south Atlantic. We verified that this was the case by comparing nest signatures detected on these satellite images with field reports of occupied nests. We found that the locations of these nest signatures determined from satellite images agreed closely with the coordinates of actual nests on the ground. We used this information to determine the position and size of a previously unreported masked booby colony on the island. Thus, we show that the presence and abundance of some species can be estimated using freely available satellite imagery if a suitable signature in the satellite image can be found. Regularly updated satellite imagery of target sites could also be used for population monitoring. While this would be expensive, initial evaluation of the technique for particular species or populations can be achieved using freely available images. We encourage wildlife managers to view their study sites on Google Earth TM for evidence of their target species.
Threshold visual acuity for grating stimuli was determined in two tawny owls (a totally nocturnal... more Threshold visual acuity for grating stimuli was determined in two tawny owls (a totally nocturnal avian species). Extensive training was given in a runway apparatus in which stimuli were presented well beyond the near point at a distance of 95 cm. Stimuli were presented according to a modified Method of Constant Stimuli. At a stimulus luminance of 1.7 log mL acuity thresholds for the two birds equalled 2.7' and 3.7'. Acuity was also determined in one bird at stimulus luminance of @2 and 1.2 log mL. and equalled 34' and 25' at each luminance respectively. These thresholds are compared with those of two humans tested in the same apparatus and with previously published acuity data for other avian and nocturnal species.
The mallard duck has a retinal visual field giving 360 degrees visual coverage in the horizontal ... more The mallard duck has a retinal visual field giving 360 degrees visual coverage in the horizontal plane and a narrow binocular field of approximately uniform width (approximately equal to 20 degrees) extending through 220 degrees from the bill to directly behind the head. Measurement of the optical fields indicate that the binocular retinal field could be considerably larger than actually found. Eye movements are not of sufficient amplitude to abolish binocularity at any elevation.
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