| 1. |
- Blary, Constance, et al.
(författare)
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Detection of wind turbines rotary motion by birds : A matter of speed and contrast
- 2023
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Ingår i: Conservation Science and Practice. - 2578-4854. ; 5:10
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Tidskriftsartikel (refereegranskat)abstract
- To reduce bird collisions on wind turbines, Automatic Detection Systems have been developed to locate approaching birds and trigger turbines to slowdown to 2–3 rotations per minute (rpm). However, it is unknown whether birds can detect this reduced speed and avoid the turbine. We conducted an operant conditioning experiment on domestic doves (Streptopelia roseogrisea) and Harris's hawks (Parabuteo unicinctus) to assess their ability to discriminate between stationary and rotating miniature wind turbines, depending on the rotation speed and the contrast between the white blades and the background (only for doves for the latter). At high contrast, regardless of the speed tested, hawks were able to differentiate between the rotating and stationary turbines, while doves were not able to discriminate the slow-rotating turbine (3 rpm) from the stationary one. The discrimination threshold increased to 8 rpm for the doves when the contrast was reduced. Our results suggest that the residual wind turbine speed of 2–3 rpm may not be detected by all bird species under all environmental conditions. Increasing the contrast between wind turbines and their environment may improve the detection of low-speed rotation by some birds, otherwise, complete turbine shutdown should be recommended.
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| 2. |
- Blary, Constance L.M., et al.
(författare)
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Low achromatic contrast sensitivity in birds : a common attribute shared by many phylogenetic orders
- 2024
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Ingår i: The Journal of experimental biology. - 1477-9145. ; 227:3
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Tidskriftsartikel (refereegranskat)abstract
- Vision is an important sensory modality in birds, which can outperform other vertebrates in some visual abilities. However, sensitivity to achromatic contrasts - the ability to discern luminance difference between two objects or an object and its background - has been shown to be lower in birds compared with other vertebrates. We conducted a comparative study to evaluate the achromatic contrast sensitivity of 32 bird species from 12 orders using the optocollic reflex technique. We then performed an analysis to test for potential variability in contrast sensitivity depending on the corneal diameter to the axial length ratio, a proxy of the retinal image brightness. To account for potential influences of evolutionary relatedness, we included phylogeny in our analyses. We found a low achromatic contrast sensitivity for all avian species studied compared with other vertebrates (except small mammals), with high variability between species. This variability is partly related to phylogeny but appears to be independent of image brightness.
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| 3. |
- Cantlay, Jennifer C., et al.
(författare)
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Binocular vision and foraging in ducks, geese and swans (Anatidae)
- 2023
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - 0962-8452. ; 290:2006
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Tidskriftsartikel (refereegranskat)abstract
- Wide variation in visual field configuration across avian species is hypothesized to be driven primarily by foraging ecology and predator detection. While some studies of selected taxa have identified relationships between foraging ecology and binocular field characteristics in particular species, few have accounted for the relevance of shared ancestry. We conducted a large-scale, comparative analysis across 39 Anatidae species to investigate the relationship between the foraging ecology traits of diet or behaviour and binocular field parameters, while controlling for phylogeny. We used phylogenetic models to examine correlations between traits and binocular field characteristics, using unidimensional and morphometric approaches. We found that foraging behaviour influenced three parameters of binocular field size: maximum binocular field width, vertical binocular field extent, and angular separation between the eye-bill projection and the direction of maximum binocular field width. Foraging behaviour and body mass each influenced two descriptors of binocular field shape. Phylogenetic relatedness had minimal influence on binocular field size and shape, apart from vertical binocular field extent. Binocular field differences are associated with specific foraging behaviours, as related to the perceptual challenges of obtaining different food items from aquatic and terrestrial environments.
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| 4. |
- Lisney, Thomas J., et al.
(författare)
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Retinal topography in two species of flamingo (Phoenicopteriformes : Phoenicopteridae)
- 2020
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Ingår i: Journal of Comparative Neurology. - : Wiley. - 0021-9967 .- 1096-9861. ; 528:17, s. 2848-2863
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Tidskriftsartikel (refereegranskat)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.
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| 5. |
- Mitkus, Mindaugas, et al.
(författare)
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Raptor vision
- 2018
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Ingår i: Oxford Research Encyclopedia of Neuroscience. - : Oxford University Press. - 9780190264086
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Portugal, Steven J., et al.
(författare)
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Anomalous binocular vision in African Harrier-Hawks
- 2023
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Ingår i: Current Biology. - 0960-9822. ; 33:21, s. 1142-1143
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Tidskriftsartikel (refereegranskat)abstract
- An animal's visual field is the three-dimensional space around its head from which it can extract visual information at any instant1. Bird visual fields vary markedly between species, and this variation is likely to be driven primarily by foraging ecology1,2,3. The binocular visual field is the region in which the visual fields of the two eyes overlap; thus, objects in the binocular field are imaged by both eyes simultaneously. The binocular field plays a pivotal role in the detection of symmetrical optic flow-fields, providing almost instantaneous information on the direction of travel and the time to contact a target towards which the head or feet is travelling; thus, information from the binocular field is crucial in guiding key foraging behaviours2,3. Here, we demonstrate an unusual visual field and binocular extent above the head in African Harrier-Hawks, also known as Gymnogenes (Polyboroides typus) compared to 18 other members of the Accipitridae4,5. We argue that the observed visual field can be attributed to the unusual and specific foraging behaviour of African Harrier-Hawks.
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| 7. |
- Potier, Simon, et al.
(författare)
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Binocular field configuration in owls : The role of foraging ecology
- 2023
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - 0962-8452. ; 290:2009
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Tidskriftsartikel (refereegranskat)abstract
- The binocular field of vision differs widely in birds depending on ecological traits such as foraging. Owls (Strigiformes) have been considered to have a unique binocular field, but whether it is related to foraging has remained unknown. While taking into account allometry and phylogeny, we hypothesized that both daily activity cycle and diet determine the size and shape of the binocular field in owls. Here, we compared the binocular field configuration of 23 species of owls. While we found no effect of allometry and phylogeny, ecological traits strongly influence the binocular field shape and size. Binocular field shape of owls significantly differed from that of diurnal raptors. Among owls, binocular field shape was relatively conserved, but binocular field size differed among species depending on ecological traits, with larger binocular fields in species living in dense habitat and foraging on invertebrates. Our results suggest that (i) binocular field shape is associated with the time of foraging in the daily cycle (owls versus diurnal raptors) and (ii) that binocular field size differs between closely related owl species even though the general shape is conserved, possibly because the field of view is partially restricted by feathers, in a trade-off with auditory localization.
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| 8. |
- Potier, Simon, et al.
(författare)
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Eye Size, Fovea, and Foraging Ecology in Accipitriform Raptors
- 2017
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Ingår i: Brain, Behavior and Evolution. - : S. Karger AG. - 0006-8977 .- 1421-9743. ; 90:3, s. 232-242
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Tidskriftsartikel (refereegranskat)abstract
- Birds with larger eyes are predicted to have higher spatial resolution because of their larger retinal image. Raptors are well known for their acute vision, mediated by their deep central fovea. Because foraging strategies may demand specific visual adaptations, eye size and fovea may differ between species with different foraging ecology. We tested whether predators (actively hunting mobile prey) and carrion eaters (eating dead prey) from the order Accipitriformes differ in eye size, foveal depth, and retinal thickness using spectral domain optical coherence tomography and comparative phylogenetic methods. We found that (1) all studied predators (except one) had a central and a temporal fovea, but all carrion eaters had only the central fovea; (2) eye size scaled with body mass both in predators and carrion eaters; (3) predators had larger eyes relative to body mass and a thicker retina at the edge of the fovea than carrion eaters, but there was no difference in the depth of the central fovea between the groups. Finally, we found that (4) larger eyes generally had a deeper central fovea. These results suggest that the visual system of raptors within the order Accipitriformes may be highly adapted to the foraging strategy, except for the foveal depth, which seems mostly dependent upon the eye size.
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| 9. |
- Potier, Simon, et al.
(författare)
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High resolution of colour vision, but low contrast sensitivity in a diurnal raptor
- 2018
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Ingår i: Proceedings of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2954 .- 0962-8452. ; 285
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Tidskriftsartikel (refereegranskat)abstract
- Animals are thought to use achromatic signals to detect small (or distant) objects and chromatic signals for large (or nearby) objects. While the spatial resolution of the achromatic channel has been widely studied, the spatial resolution of the chromatic channel has rarely been estimated. Using an operant conditioning method, we determined (i) the achromatic contrast sensitivity function and (ii) the spatial resolution of the chromatic channel of a diurnal raptor, the Harris's hawk Parabuteo unicinctus The maximal spatial resolution for achromatic gratings was 62.3 c deg-1, but the contrast sensitivity was relatively low (10.8-12.7). The spatial resolution for isoluminant red-green gratings was 21.6 c deg-1-lower than that of the achromatic channel, but the highest found in the animal kingdom to date. Our study reveals that Harris's hawks have high spatial resolving power for both achromatic and chromatic vision, suggesting the importance of colour vision for foraging. By contrast, similar to other bird species, Harris's hawks have low contrast sensitivity possibly suggesting a trade-off with chromatic sensitivity. The result is interesting in the light of the recent finding that double cones-thought to mediate high-resolution vision in birds-are absent in the central fovea of raptors.
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| 10. |
- Potier, Simon, et al.
(författare)
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How fast can raptors see?
- 2020
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Ingår i: The Journal of experimental biology. - : The Company of Biologists. - 1477-9145 .- 0022-0949. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- Birds, and especially raptors, are highly visual animals. Some of them have the highest spatial resolving power known in the animal kingdom, allowing prey detection at distance. While many raptors visually track fast-moving and manoeuvrable prey, requiring high temporal resolution, this aspect of their visual system has never been studied before. In this study, we estimated how fast raptors can see, by measuring the flicker fusion frequency of three species with different lifestyles. We found that flicker fusion frequency differed among species, being at least 129 Hz in the peregrine falcon, Falco peregrinus, 102 Hz in the saker falcon, Falco cherrug, and 81 Hz in the Harris's hawk, Parabuteo unicinctus We suggest a potential link between fast vision and hunting strategy, with high temporal resolution in the fast-flying falcons that chase fast-moving, manoeuvrable prey and a lower resolution in the Harris's hawk, which flies more slowly and targets slower prey.
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