{"id":40994,"date":"2023-10-22T20:44:41","date_gmt":"2023-10-22T20:44:41","guid":{"rendered":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40994"},"modified":"2023-10-24T19:09:03","modified_gmt":"2023-10-24T19:09:03","slug":"sensory-ecology-of-birds","status":"publish","type":"post","link":"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40994","title":{"rendered":"Sensory Ecology of Birds"},"content":{"rendered":"<p id=\"top\" \/>\n<p><em>by Graham Martin<\/em><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Birds&#8217;eye views<\/h3>\n\n\n\n<p>This conservatism among birds has been argued to be the result of fundamental constraints that arise from the requirements that limit all self-powered flying organisms and indeed, all flying machines. &#8211; p.4<\/p>\n\n\n\n<p>Although most birds lack outer ears, those that do have them show remarkable abilities for the location of sounds. &#8211; p.8<\/p>\n\n\n\n<p>In fact, flight is probably controlled within constraints imposed primarily by the requirements for controlling not the position of the whole body, but by the exacting requirements for controlling the position of just a small part of it, the bill. &#8211; p.8<\/p>\n\n\n\n<p>In short, all animals share the same planet but they live in different worlds, The human perspective of the world is as specialized or peculiar as is that of other species. Human senses do not provide a monopoly on the reality of the world, nor do they provide a baseline from which all other species&#8217; views can be considered to deviate. &#8211; p.9<\/p>\n\n\n\n<p>His definition states clearly that sensory ecology is about the information which guides an organisms interactions with its environment. &#8211; p.17<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Vision<\/h3>\n\n\n\n<p>It is dangerous to assume that because humans have been ingenious enough to measure a particular aspect of an animal then, inevitably, there will have been natural selection specifically for that aspect. What humans measure may be a by-product, an epiphenomenon of selection for another capacity, or the capacity that is measured may be a compromise that results from a trade-off between competing sources of selection. &#8211; p.23<\/p>\n\n\n\n<p>Simply seeing more differences between colours is unlikely to have been the driver of natural selection; it is the spatial information about objects that will have driven selection in the direction of detecting finer spectral differences within particular parts of the spectrum. &#8211; p.23<\/p>\n\n\n\n<p>We can also experience how our uncertainty about seeing objects and surfaces fluctuates at low light levels. As we continue to look at any one part of the dimly lit scene, the amount of detail (and the interpretation that our brain can put upon it) changes, sometimes quite dramatically; a crouching cat, a branch, a star, may come and go, all as a result of there being few photons to detect and the uncertainty of their detection and low spatial resolution. &#8211; p.25<\/p>\n\n\n\n<p>The converse of all these arguments is that the highest resolution &#8211; the detection of the finest degree of detail in a scene &#8211; can be achieved only at high light levels. &#8211; p.26<\/p>\n\n\n\n<p>It is likely that in each species there is a unique arrangement of photoreceptors and hence a unique pattern in the way that information is extracted from the environment surrounding a bird. The drivers of these different patterns of information probably lie in the control of different keys task in different environments. &#8211; p.34<\/p>\n\n\n\n<p>In essence, the finer the differences in wavelength that can be detected by an animal&#8217;s vision system, the finer the spatial detail that it can detect in its environment. &#8211; p.35<\/p>\n\n\n\n<p>Thus at low light levels similar sensitivity in the spectrum, and the absence of colour vision, will be found across all bird species. Indeed, at low light levels, these aspects of vision will be similar in birds to that of humans and other mammals, and probably to most vertebrates. &#8211; p.40<\/p>\n\n\n\n<p>Although not so striking as these fields in dove retinas, other work has shown systematic differences in the distributions of cone receptors types (classified by the colour of their oil droplets) in the eyes of other birds. These tend to show a gradient in the relative abundance of different receptor types across the retina. These suggest that marked interspecific differences exist in colour vision and spectral sensitivity within a retina and that these differences are correlated with specific perceptual challenges posed by life in different environments and the conduct of different tasks. &#8211; p.43<\/p>\n\n\n\n<p>These patterns may be roughly circular with a very high concentration at the centre and a gradual decline of cell density away from the centre. In some species, more than one region of high concentration can occur, while in others, high densities of receptors may occur in linear bands of various lengths relative to the width of the entire retina, and these are typically arranged so that they project approximately horizontally when the birds head is held in its usual resting or flight posture. &#8211; p.45<\/p>\n\n\n\n<p>Understanding the function of these ganglion cell distribution patterns visual ecology of a particular species is often not straightforward, especially in the context of individual variation. However, the usual functional explanations refer to either a role in foraging (the detection of individual items in the frontal or lateral field of view) (Figure 2.10), or the detection of predators and vigilance behaviour (the detection of predators both laterally or from behind, and usually in the direction of the horizon), rather than a role in the control of locomotion. &#8211; p.47 <em>Suggests that the image analysis part of vision can compensate for variations (when needed)<\/em><\/p>\n\n\n\n<p>It is important to note that in both the bustards and storks as illustrated here, and for that matter all other birds, forward (binocular) vision is, in fact, achieved by the use of the periphery of the optical system of each eye (Figure 2.15)- This is in marked contrast to humans in which it is central vision that looks in the forward direction. In birds, the central axis of each eye always looks laterally (Figure 2.31). &#8211; p.55<\/p>\n\n\n\n<p>It is important to consider the function of high resolution in birds. The highest resolution may not function to aid the detection of very small objects close by, but it is probably particularly important for the detection of larger objects at a great distance. This seems to be the case in the larger raptors. &#8211; p.60<\/p>\n\n\n\n<p>Put simply, it is more difficult to bring light of shorter wavelengths to a sharp focus compared to light in the green or yellow parts of the visible spectrum. Without elaborations of the optical systern to overcome such dispersion of light at shorter wavelengths, there is likely to be greater blur in an image formed by UV light. For this reason, there is good reason to filter out UV light and, indeed, this is what occurs in many eyes (such as our own) in which the cornea and\/or lens act as UV filters. Thus, it would be predicted that eyes which have the highest resolution should not be using the UV end of the spectrum. &#8211; p.60<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Hearing and olfaction<\/h3>\n\n\n\n<p>Determining direction is a purely sensory ability, but determining distance (often referred to as sound ranging) is primarily a cognitive ability in that it appears to depend upon experience and familiarity with the characteristics of known sounds. &#8211; p.73 <em>Vision is more about understanding the deviations of light by non-emittive surfaces, whereas hearing is more about discounting deviations of sound to identify their source.<\/em> <\/p>\n\n\n\n<p>These small between-ear differences in birds have the effect of greatly reducing the accuracy with which the directions of sounds can be determined compared with mammals. &#8211; p.74<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Touch, taste and magnetoperception<\/h3>\n\n\n\n<p>In parrots, bill tip organs may function in the manipulation of objects held in the bill tip and also in the positioning of the bill when it is used as a &#8216;third limb&#8217; in climbing. The visual fields and bill shape of parrots preclude them from seeing their own bill and so somatosensory control of bill position with respect to twigs and branches when climbing may be important when the bill is used in this specialized way. &#8211; p.100<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Birds in the dark: complementary and partial information<\/h3>\n\n\n\n<p>For example, if some objects are just detectable at a particular distance at a high light level, then when acuity decreases ten-fold those same objects will have to be ten times closer to be detected. This means that the great utility of vision over other senses, its telereceptive abilities, reduces progressively as light levels fall. &#8211; p.118<\/p>\n\n\n\n<p>One particularly important aspect of this variability of naturally occurring light levels is that variation is always larger during the night compared with the day. In essence, daytime is a relatively stable light environment; night-time is not. &#8211; p.120<\/p>\n\n\n\n<p>The important effect of light level variability during the night at any one location is that the spatial resolution of an animal&#8217;s vision must be changing continuously by non-trivial amounts. Consequently the spatial information, and hence the detectability of objects and surfaces, also changes continuously. &#8211; p.123<\/p>\n\n\n\n<p>Furthermore, the lower the light levels the greater the problem, and detection distances are not only smaller but less predictable inside a wood than outside it, because of the shading effects of the canopy. &#8211; p.124<\/p>\n\n\n\n<p>This need for familiarity with both sounds and perch positions introduces a particular behavioural adaptation which may be a vital component to nocturnality in woodland owl species. &#8211; p.130 <em>Why consider this as an exception? It might only be a need for tighter sensorymotor loops.<\/em><\/p>\n\n\n\n<p>This introduces a clear hypothesis that there is a cognitive component to nocturnality. Knowledge of the spatial structure and sound degradation characteristic within a particular location are built up when light levels are high, and this knowledge allows mobility and accurate sound ranging when light levels are low. &#8211; p. 130 <em>It is a telling example of habitat.<\/em><\/p>\n\n\n\n<p>The fact that tapeta are present in at least some nightjars (but they are absent from all other bird species) suggests that evolution has favoured sensitivity over resolution. &#8211; p.149 <em>Same for cats? Why?<\/em><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Birds underwater: a paucity of information<\/h3>\n\n\n\n<p>First, going through the water surface changes the optical properties of the eye, and it has been assumed that an ideal amphibious eye should be able to function as well in water as it does in air. Whether this is the case is unclear. Second, light levels immediately fall and continue to do so with increasing depth, and the spectral composition of the ambient light also changes with depth. Third, because birds are air breathers, the majority of divers stay down for only short periods, just a few minutes at most. This means that they transition very rapidly between different light levels both as they dive and as they travel back to the surface. Such rapid transformation in light levels is unlikely to allow sufficient time for the retinal dark adaptation to occur (Warrant 2008). Fourth, many diving species forage during night-time, compounding the loss of light. &#8211; p.161<\/p>\n\n\n\n<p>Some foraging would seem to be more exacting in that it involves the detection of mobile prey which may have evasive strategies to avoid capture. Other foraging poses less exacting sensory challenges in that it involves sessile foods but they have to be detected and then detached from a surface. Although detection of sessile items may be challenging, once found they do not have to be pursued and caught. The foraging of the diving petrels differs from all the other groups as the prey is often, perhaps always, detected from above the water surface, as the birds fly over or sit upon the water surface, whereas in all other types of foraging the actual search for food does not begin until the birds are underwater. &#8211; p.162<\/p>\n\n\n\n<p>Thus a terrestrial eye immersed in water will lose the refractive power of the cornea and will become long sighted. The loss of corneal refractive power on entering water has two other important consequences: the brightness of the image is reduced because the effective size of the entrance pupil becomes smaller (in air the cornea magnifies the size of the real pupil), and the limits of the visual field of each eye will decrease. One adaptation which may have evolved to reduce the magnitude of these changes in the eyes of amphibious species has been relatively flat (hence lowrefractive power) corneas. &#8211; p.163<\/p>\n\n\n\n<p>In addition to these reductions in irradiance, there is a very marked differential spectral absorption of light with increasing depth. Again, this is a property of the clearest natural waters, such that by 200m deep, the available light becomes noticeably blue to the human eye. This indicates that there has been selective absorption of light at longer wavelengths and also at shorter (violet and ultraviolet) wavelengths. &#8211; p.166 + Fig 7.3<\/p>\n\n\n\n<p>The effects described above are a property of pure water but this rarely occurs in nature. Pure waters tend not to be foraging environments because they are nutrient poor and would not support significant number of organisms that can be foraged for. In most waterbodies, and certainly in most foraging waters, the light environment is more complex due to the presence of suspended matter (living organisms, products of decay, dissolved and suspended minerals) which serve to scatter light even more and add other selective spectral filtering effects. The cumulative effects of these are that light will be attenuated at depths of 100-200 m by much more than the 100-fold of pure water, and the spectrum of light may have its peak shifted than the 100-fold of pure water, and the spectrum may have its peak shifted to the visible spectrum with very little, or no light, at shorter wavelengths and also none at wavelengths beyond about 550 nm. &#8211; p.168<\/p>\n\n\n\n<p>It has been shown that when entering a natural cavity a bird may transition from bright light to dark cavity interiors in less than a second and that light levels fall 10,000-fold. There is no information as to how these birds&#8217; eyes can cope with these rapid changes, and it may be chat on entering a cavity their vision is simply not well adapted to the darkness. The birds may be able to detect only very low spatial detail, and they rely primarily upon information from hearing and tactile cues to feed young or attend to their eggs. &#8211; p.168<\/p>\n\n\n\n<p>It seems highly likely (given the range of low light conditions, the turbid conditions of some waterbodies, the cryptic nature of prey, and the low acuity the birds) that cormorants do not identify the prey item\u2014they simply lunge at an escaping blur. Of course, if the blur is escaping it is highly likely to be edible food. &#8211; p.176 <em>Importance of motion!<\/em><\/p>\n\n\n\n<h3 class=\"wp-block-heading\">What drives birds senses?<\/h3>\n\n\n\n<p>The discussion which follows suggests that this is indeed the case and concludes with the proposal that the primary driver of sensory capacity in birds is foraging. Furthermore, because of the unique use of the bill in the foraging of birds, the ke\/ driver can be further refined to the quite specific informational demands for control of bill position and the timing of the bill s arrival at a target. The most important task that drives vision in birds is the detection of predators, but it seems that accurate bill positioning and predator detection usually make antago~ nistic informational demands with the result that there is frequendy a trade-off between these two demands, but getting the bill in the right place and at the right time takes precedence over predator detection. This is, perhaps, because predator detection can usually be enhanced by behavioural adaptations involving scanning as well as the use of senses additional to vision. But accurate bill position and tirning can only be achieved using visual information. The outcome of the trade-offs between the control of bill position and detecting predators depends upon details of the foraging ecology of each species with the result that there are many subtle variations between species. The final conclusion of this chapter is that all other behaviours, including flight and reproduction, are conducted within the constraints set by the sensory information that is necessary to guide foraging and the requirements of predator detection. &#8211; p.187<\/p>\n\n\n\n<p>It seems highly likely that fine spatial resolution may have evolved, as in the case of diurnal raptors, for the detection of objects (prey items) at great distances rather than to perceive fine detail close by. &#8211; p. 188 This means that habitats are devoid of very thin (motionless?) obstacles<\/p>\n\n\n\n<p>Each dietary type is associated with particular methods of food acquisition nearly all of which involve using the bill as the sole tool. Pecking, lunging, probing, excavation, aerial pursuit, pursuit under water, grazing, filtering mud and water, trawling water and the air: all of these foraging tasks pose a rich array of per&#8217; ceptual challenges. Furthermore, these tasks must be dealt with frequently, almost continuously, by a bird throughout its life. Retrieving sufficient information from. the environment to allow birds to do these tasks must be the subject of exacting natural selection. &#8211; p.188<\/p>\n\n\n\n<p>It is argued below (8.5) that differences in the visual fields of birds provideateL-s for understanding how the different perceptual challenges presented by foraging and by predator detection have been traded-off within visual systems. Studies of visual fields also exemplify the fine tuning of vision to different perceptual challenges. Such tuning has resulted in functionally significant differences in visual ecology even between species which are in the same genus. This indicates that sensory capacities can be fine-tuned by the competing demands of different tasks. &#8211; p.191<\/p>\n\n\n\n<p>However, compared with most vertebrates, including all birds, human eye placement and our resultant visual field is unusual (Figure 2.14). Birds are, in effect, surrounded by their visual world and they &#8216;flow through&#8217; it, rather than move into it (Martin 2012). As a bird moves through the world an object can be tracked from directly in front to the rear of the head. &#8211; p.192 How to transfer visually different fields? Reduce disparity info and widen FoV? How to deal with the inevitable distorsion of straight lines?<\/p>\n\n\n\n<p>In no birds do the eyes directly forwards and for many birds the eyes not only look sideways but they axe also positioned more towards the top of the skull and the axes of the eyes project slightly upwards, rather than horizontally. The result is that, for the large majority of birds, the visual world is all around; there is little or n.o blind area above or to the rear of the head. &#8211; p.192<\/p>\n\n\n\n<p>In birds, a target is usually detected visually in the lateral field of view of a single eye, probably employing a region with the highest quality optics and the highest retinal resolution (Martin 2009) (Chapter 2, 2j)- After detection, visual control is passed to the frontal field, within which the direction of the bill projects, but this may occur at only a relatively close distance from, or short time before, contact with the target. This allows the accurate direction of the bill towards the target and accurate timing of its arrival, so that bill opening can be co-ordinated with arrival at the target and the object grasped in the bill. In some birds, pecking has a ballistic phase and the eyes are closed during the final approach towards the target. In other birds, prey may be taken in the feet which are swung up into the central projection of the binocular field just prior to prey capture. &#8211; p.195<\/p>\n\n\n\n<p>Total panoramic vision appears to have evolved independently in two quite different bird orders: ducks (Anseriformes) and shorebirds (Charadriiformes). Only a few species in these taxa have totally panoramic vision, but those that do have it share a common feature in that their foraging does not rquire visual control of bill position; instead, foraging relies upon tactile cues from bill tip organs (Chapter 4, 4.1.2). It appears that, freed from the constraint for the accurate visually guided control of bill position, natural selection has favoured the evolution of comprehensive visual coverage about the head to aid predator detection. Crucially, however, the width of binocular overlap in these species is minimal, between 5\u00b0 and 10\u00b0 (Figure 8.1). Yet, these birds are capable of fast flight often in complex habitats, and this suggests that a frontal binocular field of this minimal width is sufficient for the control of flight. &#8211; p.195<\/p>\n\n\n\n<p>Not requiring visual cues to guide foraging is not in itself sufficient to lead to the evolution of comprehensive vision. It is also necessary that the bill does not require fine visual control for any task, not just foraging. Thus comprehensive vision is, in fact, found only among birds which also do not need to position their bills accurately for two other key tasks: nest construction and the provisioning of young. &#8211; p.197<\/p>\n\n\n\n<p>It is argued below that, with the possible exception of owls, binocularity in birds does not have a higher order visual function which results in the perception of solidity and relative depth. Such perception may be something found uniquely among mammals. It is argued that binocularity in birds is, in fact, a consequence of the requirement for having a portion of the visual field that looks in the direction of travel; hence each eye must have a contralateral projection, that is, each eyemus look across the central plane of the head. It is true that this results in binocular vision, but its function is not to do with the perception of relative depth, rather it is to do with the direct control of bill position, and in some birds the control position of their feet (Martin 2009) &#8211; This suggests that binocular vision plays only a minor role in the control of locomotion including flight. In the majority of birds. the function of binocularity would seem to lie in what each eye does independently rather than in what the two eyes might be able to do together. &#8211; p.198<\/p>\n\n\n\n<p>This similarity in binocular field configuration across such diverse groups of? birds, and across such diverse feeding techniques, suggests a degree of convergence upon a binocular field width that is optimal for a particular purpose. That is, a 20\u00b0\u201430\u00b0 binocular field is as broad as it needs to be to fulfil a particular function that is common to all of these species. Beyond such a width, there is little advantage co be gained, and in the majority of birds it is the extent of the peripheral fields tha are maximized to reduce vulnerability to attack by predators. There would seem to be a trade-off between the demands for accurately controlling bill or feet position when approaching a target (which requires some degree of contralateral vision), and the requirement to gain as comprehensive a view of the world as is possible &#8211; p.200<\/p>\n\n\n\n<p>Seeing what lies perpendicularly beneath the bill clearly has the advantage that a foraging heron can remain motionless, monitoring what is going on below it, while it waits for a prey item, such as a frog or fish, to come within striking range. Because these prey species have evolved rapid escape responses, herons may get only a one-strike chance to catch each item. Therefore, monitoring what is going on below, without having to move the head or body&gt; and waiting for a prey item to come within striking range, is clearly a significant advantage for a heron &#8211; p.201 Project different areas on a 3D environment? Capture animal motion from videos?<\/p>\n\n\n\n<p>In the majority of birds, the eyes move by up to about 20\u00b0 and furthermore eye movements are not conjugate, that is, the eyes do not move together and same direction as they do in humans. &#8211; p.203<br>The fact that there cannot be simple corresponding points that can underlie binocular vision in bircLs is already clear in Figures 2.3 and 2.15 which showed sections through the visual fields of owls and ostriches. It provides further support for the idea that stereopsis and the perception of relative depth are not functions of binocular vision in the majority of birds. &#8211; p.204 Maybe binocular stereopsis is still possible through active eye synchronisation?<\/p>\n\n\n\n<p>The wider binocular field of owls may also have an adaptive explanation that is associated with prey capture rather than the nocturnal habit. In owls, the bill lies below the binocular field and in catching prey the feet are swung up before the bird&#8217;s face, directly into the binocular field, and directly into the flight path of the bird. It seems likely that the binocular field is used in conjunction with accurate sound localization to guide the feet in the final stages of prey capture. In the final approach towards a prey item, the feet are raised and the talons spread wide to fill the visual field in front of the head, which is also the region where sound localization is most accurate (Martin 1986a). Clearly timing the spreading of the talons In tion is most accurate (Martin 1986a). Clearly timing tne spreading or the taions in birds. &#8211; p.206<br>Clearly, if selective pressure has been to evolve a large eye to maximize resolution, it would be maladaptive to compromise that resolution by degrading the retinal image with light scattered from an image of the sun. Smaller eyes, on the other hand, can only ever have lower acuitry and so veiling glare produced by light scattered from a retinal image of the sun may do relatively little to degrade the image generally and lower spatial resolution across the visual field. &#8211; p.209<\/p>\n\n\n\n<p>Thus, the regions within the visual field where there is high spa&#8217; tial resolution, which at high light levels are enhanced by colour vision, are indicated by the high densities of photoreceptors and ganglion cells (Chapter 2, 2.7,1. Figures 2.6 and 2.7). These regions projects outwards, laterally, on both sides of the bird, not directly forwards, and in the majority of birds forward vision served by regions of high photoreceptor and ganglion cell density. &#8211; p.210<\/p>\n\n\n\n<p>That is, the bird does not usually sight the prey into its binocular field. until just before prey capture. Thus distant prey is probably initially detected usi ng lateral high resolution vision while the control of the bill and feet close of prey capture probably employs frontal, binocular vision, and this comes into play only at close range. However, there is evidence that other falcon species may use frontal vision quite early on in the pursuit of prey and switch between the different foveas during a pursuit flight by turning the head. &#8211; p.210 As if birds engage and switch between different vision modes &#8220;behaviorally&#8221;<\/p>\n\n\n\n<p>It has been shown convincingly that birds use flow-field information to control apparently exacting tasks. For example Northern Gannets Mortis bassanus and hummingbirds (Trochilidae) when carryout manoeuvres that require accurate visual information regarding location and speed of approach to a target employ flow-field information, and there is increasing evidence that birds use flow-field information to guide flight and landing. &#8211; p.211 Locomotion would thus be more based on flow than accuity. Are there limits though?<\/p>\n\n\n\n<p>It can be concluded that binocularity in birds functions to provide information on the direction of travel and time-to-contact a target. However, this information can be provided by each eye independently and for this reason it might be more appropriate to refer to contralateral vision&#8217; rather than &#8216;binocular vision, since the latter brings with it assumptions concerning the precept of solidity and stereopsis with which binocular vision in birds does not appear to be generally associated. &#8211; p.211<\/p>\n\n\n\n<p>There are pigments with lambda_max at 365 nm, referred to as ultraviolet sensitive (UVS) and those in which lambda_max is at 410 nm, referred to as violet sensitive (VS). It is possession of the UVS pigment which gives the oscine passerines, gulls, ostriches, and parrots their visual sensitivity into the UV part of the spectrum. &#8211; p.214<\/p>\n\n\n\n<p>Rather colour vision in birds would seem to have general utility for enhancing spatial resolution across the spectrum. In some bird taxa that spectrum extends to the shorter UV wavelengths that human eyes cannot detect. Thus colour vision is probably best viewed in birds, even in those which see into the UV, as maintained or driven by unspecified ubiquitous behaviours which require fine spatial resolution. It seems more likely that plumage signals in the UV, and fruit and foliage differential reflectivity in the UV, have evolved in response to UV sensitivity of birds. That is, it is bird colour vision which has driven the spectral qualities of certain targets, rather than the other way around. &#8211; p. 214 Increase in resolution or discrimination (spatial &amp; in depth)?<\/p>\n\n\n\n<p>For a human to experience a real bird&#8217;s eye view is impossible. However, trying to fully explore what this means is rewarding for we soon find that our experience of the world provides but a small insight into the world that supports our existence. &#8211; p.216<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">The sensory ecology of collisions and entrapment<\/h3>\n\n\n\n<p>Rather, what might be crucial is determining time-to-contact an obstacle since this will determine whether avoiding manoeuvres are possible. This is probably also true of humans. The most vital visual information beyond recognition of an object is the object&#8217;s position and, if there is relative speed between the object and the observer, information on time-to-contact. The actual distance of an object from a bird may be of little importance compared with its direction and the time it may take to make contact with it. &#8211; p. 221<\/p>\n\n\n\n<p>In humans, the section of the visual field that is used for detailed analysis of objects looks directly forward. However, this is not the case in birds. For humans, the detailed world lies ahead, whereas for birds the detailed world lies laterally. &#8211; p.222 So collision would be likely with an object ahead that would not have been registered earlier<\/p>\n\n\n\n<p>Preferential use of lateral vision has been described both in tasks involving close objects, which require approach or a pecking response towards the object, and in tasks that involve flight towards distant objects. Thus a Peregrine Falcon ap proaching its prey seems to be primarily under the control of lateral rather than frontal\/binocular vision, in that the bird typically approaches along a curving path that would allow the prey object to be kept in the vision of the laterally projecting fovea of one eye until the final closure upon the prey object, when transfer is passed to frontal vision at close range. &#8211; p.223 Is half of the FoV not attended when laterally fixating?<\/p>\n\n\n\n<p>Do birds have available to them a rich array of info rmation to guide their flight or are they sometimes executing tasks at the limits of the information that is available to them? Is there often a paucity of information? Two further key questions arise. First, when flying can birds adjust their rate of gain of information to meet the perceptual challenge of the environment? For example, under conditions of reduced visibility (which will result in a reduced rate of information gain) ? can birds slow down and adjust their rate of gain of information to meet the perceptual challenge? Second, in open habitats are flying birds always looking ahead? &#8211; p.225<\/p>\n\n\n\n<p>Thus if birds are to fly under non-ideal perceptual conditions, or visibility conditions change during a flight, they cannot act in the way that a careful car driver can and reduce their speed in order to gain information at a rate sufficient to match the new perceptual challenge. &#8211; p.226<\/p>\n\n\n\n<p>Why should birds in flight pitch their head down in this manner? In the case of the terns, vultures, and eagles this seems to be directly linked with foraging behaviour, since prey and carrion are principally detected on the ground or in water below. In the case of bustards and cranes, birds may not be looking for individual prey items but for foraging patches, groups of other birds, or searching for roost sites. However, in all cases the birds are more interested in what is below them than what lies ahead in the (presumed) open airspace. It seems clear that when these birds are &#8216;looking downwards&#8217; when foraging they are simply not looking where they are going. They may occasionally raise their head to see forwards but even then they may look but fail to see&#8217;. This is because throughout the whole of their evolution, when flying above natural terrains at a height defined by the tallest trees, the airspace has been empty, and sparse spatial information has been sufficient to ensure safe flight. There would seem to be a parallel here with the reliance on sparse information that is sufficient to guide amphibious birds when underwater. &#8211; p.227<\/p>\n","protected":false},"excerpt":{"rendered":"<p>by Graham Martin Birds&#8217;eye views This conservatism among birds has been argued to be the result of fundamental constraints that arise from the requirements that limit all self-powered flying organisms and indeed, all flying machines. &#8211; p.4 Although most birds lack outer ears, those that do have them show remarkable abilities for the location of &#8230; <a title=\"Sensory Ecology of Birds\" class=\"read-more\" href=\"https:\/\/www.labri.fr\/perso\/barla\/blog\/?p=40994\" aria-label=\"Read more about Sensory Ecology of Birds\">Read more<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[621],"tags":[],"class_list":["post-40994","post","type-post","status-publish","format-standard","hentry","category-books"],"_links":{"self":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40994","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=40994"}],"version-history":[{"count":7,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40994\/revisions"}],"predecessor-version":[{"id":41004,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=\/wp\/v2\/posts\/40994\/revisions\/41004"}],"wp:attachment":[{"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=40994"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=40994"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.labri.fr\/perso\/barla\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=40994"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}