Penglihatan burung: Perbedaan antara revisi
Tidak ada ringkasan suntingan |
Tidak ada ringkasan suntingan |
||
| Baris 40: | Baris 40: | ||
[[Koroid]] adalah lapisan yang terletak di belakang retina yang berisi [[pembuluh nadi]] kecil dan [[pembuluh balik]] yang mengalirkan darah ke retina. Koroid mengandung [[melanin]], [[pigmen]] yang memberikan warna gelap pada mata, membantu untuk mencegah gangguan dari refleksi. |
[[Koroid]] adalah lapisan yang terletak di belakang retina yang berisi [[pembuluh nadi]] kecil dan [[pembuluh balik]] yang mengalirkan darah ke retina. Koroid mengandung [[melanin]], [[pigmen]] yang memberikan warna gelap pada mata, membantu untuk mencegah gangguan dari refleksi. |
||
<!-- JANGAN DIHAPUS, MAU DITERJEMAHKAN |
|||
<!-- |
|||
==Light perception== |
|||
[[File:BirdVisualPigmentSensitivity.svg|thumb|The four pigments in a bird's [[Cone cell|cones]] extend the range of colour vision into the [[ultraviolet]].<ref name=hart>{{cite journal|last= Hart|first= NS |year=2000 |title= Visual pigments, cone oil droplets and ocular media in four species of estrildid finch|journal= Journal of Comparative Physiology A|volume=186|issue=7–8|pages=681–694|url=http://www.uq.edu.au/~uqnhart/Hart_finches.pdf|format=PDF|doi= 10.1007/s003590000121|last2= Partridge|first2= J.C.|last3= Bennett|first3= A.T.D.|last4= Cuthill|first4= I.C.}}</ref><ref name =ref7>The effect of the coloured oil droplets is to narrow and shift the absorption peak for each pigment. The absorption peaks without the oil droplets would be broader and less peaked, but these are not shown here.</ref>]] |
|||
There are two sorts of light receptors in a bird’s eye, [[Rod cell|rods]] and [[Cone cell|cones]]. Rods, which contain the visual pigment [[rhodopsin]] are better for night vision because they are sensitive to small quantities of light. Cones detect specific colours (or wavelengths) of light, so they are more important to colour-orientated animals such as birds.<ref name= "Goldsmith"/> Most birds are [[tetrachromacy|tetrachromatic]], possessing four types of cone cells each with a distinctive maximal absorption peak. In some birds, the maximal absorption peak of the cone cell responsible for the shortest wavelength extends to the [[ultraviolet]] (UV) range, making them UV-sensitive. <ref name=wilkie>{{cite journal |last=Wilkie |first=Susan E. |year=1998 |title=The molecular basis for UV vision in birds: spectral characteristics, cDNA sequence and retinal localization of the UV-sensitive visual pigment of the budgerigar (Melopsittacus undulatus)|journal=[[Biochemical Journal]] |volume=330 |pages=541–47 |pmid=9461554 |last2=Vissers |first2=PM |last3=Das |first3=D |last4=Degrip |first4=WJ |last5=Bowmaker |first5=JK |last6=Hunt |first6=DM |pmc=1219171 |issue=Pt 1}}</ref> Pigeons have an additional pigment and are therefore [[Pentachromacy|pentachromatic]].<ref name = "Varela"/> |
|||
The four spectrally distinct cone pigments are derived from the protein [[opsin]], linked to a small molecule called [[retinal]], which is closely related to [[vitamin A]]. When the pigment absorbs light the retinal changes shape and alters the membrane potential of the cone cell affecting neurones in the ganglia layer of the retina. Each neurone in the ganglion layer may processes information from a number of [[photoreceptor cell]]s, and may in turn trigger a [[action potential|nerve impulse]] to relay information along the optic nerve for further processing in specialised visual centres in the brain. The more intense a light, the more photons are absorbed by the visual pigments, the greater the excitation of each cone, and the brighter the light appears.<ref name= "Goldsmith">{{cite journal|last=Goldsmith |first=Timothy H. |month=July |year=2006 |title=What birds see |journal=Scientific American |pages= 69–75 |url=http://seit.unsw.adfa.edu.au/coursework/ZEIT8227/WhatBirdsSee21090424.pdf |format=PDF }}</ref> |
|||
[[File:BirdCone.png|thumb|left|Diagram of a bird cone cell]] |
|||
By far the most abundant cone pigment in every bird species examined is the long-wavelength form of [[iodopsin]], which absorbs at wavelengths near 570 nm. This is roughly the spectral region occupied by the red- and green-sensitive pigments in the primate retina, and this visual pigment dominates the colour sensitivity of birds.<ref name = "Varela"/> In [[penguin]]s, this pigment appears to have shifted its absorption peak to 543 nm, presumably an adaptation to a blue aquatic environment.<ref name="Bowmaker">{{cite journal|last=Bowmaker |first=J. K. |month=January|year=1985 |title=Visual pigments and oil droplets in the penguin, ''Spheniscus humbolti'' |journal=Journal of Comparative Physiology |volume=156 |issue=1|pages=71–77 |url= |format= |doi=10.1007/BF00610668|last2=Martin|first2=G. R. }}</ref> |
|||
The information conveyed by a single cone is limited: by itself, the cell cannot tell the brain which wavelength of light caused its excitation. A visual pigment may absorb two wavelengths equally, but even though their photons are of different energies, the cone cannot tell them apart, because they both cause the retinal to change shape and thus trigger the same impulse. For the brain to see colour, it must compare the responses of two or more classes of cones containing different visual pigments, so the four pigments in birds give increased discrimination.<ref name= "Goldsmith"/> |
|||
Each cone of a bird or reptile contains a [[coloured oil droplet]]; these no longer exist in mammals. The droplets, which contain high concentrations of [[carotenoid]]s, are placed so that light passes through before reaching the visual pigment. They act as filters, removing some wavelengths and narrowing the absorption spectra of the pigments. This reduces the response overlap between pigments and increases the number of colours that a bird can discern.<ref name= "Goldsmith"/> Six types of cone oil droplets have been identified; five of these have carotenoid mixtures that absorb at different wavelengths and intensities, and the sixth type has no pigments.<ref name= "Goldsmith2">{{cite journal|last=Goldsmith |first=T. H.|month= |year=1984 |title=The cone oil droplets of avian retinas |journal=Vision Research. |volume=24|issue=11 |pages=1661–1671 |url= |format= |doi= 10.1016/0042-6989(84)90324-9| pmid = 6533991| quotes =|last2=Collins|first2=JS|last3=Licht|first3=S}}</ref> The cone pigments with the lowest maximal absorption peak, including those that are UV-sensitive, possess the 'clear' or 'transparent' type of oil droplets with little spectral tuning effect. <ref>{{cite journal|last=Vorobyev|first=M.|coauthors=Osorio, D., Bennett, A. T. D., Marshall, N. J., Cuthill, I. C.|title=Tetrachromacy, oil droplets and bird plumage colours|journal=Journal of Comparative Physiology A: Neuroethology Sensory Neural and Behavioral Physiology|date=3|year=1998|month=July|volume=183|issue=5|pages=621–633|url=http://www.neurobiologie.fu-berlin.de/menzel/Pub_AGmenzel/VorobyevOsorio-et-al_JCompPhysiolA_1998.pdf}}</ref> |
|||
The colours and distributions of retinal oil droplets vary considerably among species, and is more dependent on the ecological niche utilised (hunter, fisher, herbivore) than [[gene]]tic relationships. As examples, diurnal hunters like the [[Barn Swallow]] and birds of prey have few coloured droplets, whereas the surface fishing [[Common Tern]] has a large number of red and yellow droplets in the dorsal retina. The evidence suggests that oil droplets respond to [[natural selection]] faster than the cone's visual pigments.<ref name = "Varela"/> Even within the range of wavelengths that are visible to humans, passerine birds can detect colour differences that humans do not register. This finer discrimination, together with the ability to see ultraviolet light, means that many species show sexual dichromatism that is visible to birds but not humans.<ref name=eaton >{{cite journal| last= Eaton | first= Muir D. | coauthors= | month= August| year= 2005 | title= Human vision fails to distinguish widespread sexual dichromatism among sexually "monochromatic" birds | journal=Proceedings of the National Academy of Sciences of the United States of America |url = http://ukpmc.ac.uk/articlerender.cgi?artid=515400 | volume= 102 | issue =31 | pages= 10942–10946 |format = | doi = 10.1073/pnas.0501891102| pmid= 16033870| pmc= 1182419 }}</ref> |
|||
Migratory songbirds use the Earth’s magnetic field, stars, the Sun, and polarised light patterns to determine their migratory direction. An American study showed that migratory [[Savannah Sparrow]]s used polarised light from an area of sky near the horizon to recalibrate their magnetic navigation system at both sunrise and sunset. This suggested that skylight polarisation patterns are the primary calibration reference for all migratory songbirds.<ref name= "Muheim">{{cite journal|last=Muheim |first=Rachel |month=August |year=2006 |title=Polarized light cues underlie compass calibration in migratory songbirds |journal=Science |volume=313|issue= 5788|pages= 837–839|url=http://www.angel.ekol.lu.se/~rachel/publications/JOrnithol%202007.pdf |format=PDF|doi=10.1126/science.1129709|pmid=16902138|last2=Phillips|first2=JB|last3=Akesson|first3=S}}</ref> However, it appears that birds may be responding to secondary indicators of the angle of polarisation, and may not be actually capable of directly detecting polarisation direction in the absence of these cues.<ref name= "Greenwood">{{cite journal|last=Greenwood |first=Verity J. |year=2003|title=Behavioural investigation of polarisation sensitivity in the Japanese quail (''Coturnix coturnix japonica'') and the European starling (''Sturnus vulgaris'') |journal=The Journal of Experimental Biology |volume=206 |issue= Pt 18|pages=3201–3210 |url=http://jeb.biologists.org/cgi/content/full/206/18/3201 |format= |doi=10.1242/jeb.00537| pmid= 12909701|last2=Smith|first2=EL|last3=Church|first3=SC|last4=Partridge|first4=JC}}</ref> |
|||
===Ultraviolet=== |
|||
[[File:Common Kestrel 1.jpg|upright|thumb|The [[Common Kestrel]] can detect the ultraviolet trail of its vole prey.]] |
|||
Some birds can perceive ultraviolet light<ref name=carvalho>{{cite journal|last=Carvalho|first=L. S.|coauthors=Cowling, J. A., Wilkie, S. E., Bowmaker, J. K., Hunt, D. M.|title=The molecular evolution of avian ultraviolet- and violet-sensitive visual pigments|journal=Molecular Biology and Evolution|year=2007|volume=24|issue=8|pages=1843–52|doi=10.1093/molbev/msm109|url=http://mbe.oxfordjournals.org/content/24/8/1843.full.pdf}}</ref>, which is involved in courtship. Many birds show plumage patterns in ultraviolet that are invisible to the human eye; some birds whose sexes appear similar to the naked eye are distinguished by the presence of [[ultraviolet]] reflective patches on their feathers. Male [[Blue Tit]]s have an ultraviolet reflective crown patch which is displayed in courtship by posturing and raising of their nape feathers.<ref>{{cite journal |last=Andersson|first=S. |title=Ultraviolet sexual dimorphism and assortative mating in blue tits|journal=Proceeding of the Royal Society B |year=1998 |volume=265 |issue=1395 |pages=445–50 |url=http://beheco.oxfordjournals.org/cgi/content/full/15/5/805 |doi=10.1098/rspb.1998.0315|coauthors=J. Ornborg & M. Andersson}}</ref> Male [[Blue Grosbeak]]s with the brightest and most UV-shifted blue in their plumage are larger, hold the most extensive territories with abundant prey, and feed their offspring more frequently than other males do.<ref name= "Goldsmith"/> |
|||
The bill’s appearance is important in the interactions of the [[Common Blackbird|Blackbird]]. Although the UV component seems unimportant in interactions between territory-holding males, where the degree of orange is the main factor, the female responds more strongly to males with bills with good UV-reflectiveness.<ref name = "AB64" >{{cite journal|last=Bright |first=Ashleigh.|month=August |year=2002 |title=Effects of bill pigmentation and UV reflectance during territory establishment in blackbirds |url=http://cber.bio.waikato.ac.nz/images/bbposter2.pdf |format=PDF|journal=Animal Behaviour |volume=64 |issue=2|pages=207–213|doi=10.1006/anbe.2002.3042|last2=Waas|first2=Joseph R.}}</ref> |
|||
A UV receptor may give an animal an advantage in foraging for food. The waxy surfaces of many fruits and berries reflect UV light that might advertise their presence.<ref name= "Goldsmith"/> [[Common Kestrel]]s are able to locate the trails of [[vole]]s visually. These small rodents lay scent trails of urine and faeces that reflect UV light, making them visible to the kestrels, particularly in the spring before the scent marks are covered by vegetation.<ref>{{cite journal |last=Viitala |first=Jussi |year=1995 |journal=Nature |volume=373 |issue=6513 |pages=425–27 |title=Attraction of kestrels to vole scent marks visible in ultraviolet light |doi=10.1038/373425a0 |last2=Korplmäki |first2=Erkki |last3=Palokangas |first3=Pälvl |last4=Koivula |first4=Minna}}</ref> |
|||
==Perception== |
|||
===Movement=== |
|||
[[File:Milvus milvus -Laurieston, Dumfries and Galloway, Scotland -feeding station-8.jpg|300px|thumb|right|A [[Red Kite]] flying at a bird feeding station in Scotland]] |
|||
Birds can resolve rapid movements better than humans, for whom flickering at a rate greater than 50 [[hertz|Hz]] appears as continuous movement. Humans cannot therefore distinguish individual flashes of a fluorescent light bulb oscillating at 60 Hz, but [[Budgerigar]]s and [[chicken]]s have flicker thresholds of more than 100 Hz. A [[Cooper's Hawk]] can pursue agile prey through woodland and avoid branches and other objects at high speed; to humans such a chase would appear as a blur.<ref name= "Jones">{{cite journal| last= Jones | first= Michael P | month= April | year=2007 | title= Avian vision: a review of form and function with special consideration to birds of prey | journal= Journal of Exotic Pet Medicine | volume= 16| issue= 2 | pages= 69–87| url = http://www.csulb.edu/~efernand/visualecol/Avian%20vision.pdf |format = PDF| doi = 10.1053/j.jepm.2007.03.012| last2= Pierce Jr| first2= Kenneth E.| last3= Ward| first3= Daniel}}</ref> |
|||
Birds can also detect slow moving objects. The movement of the sun and the constellations across the sky is imperceptible to humans, but detected by birds. The ability to detect these movements allows migrating birds to properly orientate themselves.<ref name= "Jones"/> |
|||
To obtain steady images while flying or when perched on a swaying branch, birds hold the head as steady as possible with compensating reflexes. Maintaining a steady image is especially relevant for birds of prey.<ref name= "Jones"/> |
|||
===Edges and shapes=== |
|||
When an object is partially blocked by another, humans unconsciously tend to make up for it and complete the shapes (See [[Amodal perception]]). It has however been demonstrated that pigeons do not complete occluded shapes.<ref>{{cite journal|author=Sekuler A B, Lee J A J, Shettleworth S J|year=1996|title=Pigeons do not complete partly occluded figures|journal=Perception |volume=25|issue=9|pages=1109–1120|doi=10.1068/p251109|pmid=8983050}}</ref> A study based on altering the grey level of a perch that was coloured differently from the background showed that [[budgerigar]]s do not detect edges based on colours.<ref>{{cite journal|author=Bhagavatula P, Claudianos C, Ibbotson M, Srinivasan M |year=2009|title= Edge Detection in Landing Budgerigars (Melopsittacus undulatus)|journal= PLoS ONE |volume=4|issue=10|page=e7301|doi=10.1371/journal.pone.0007301|pmid=19809500|pmc=2752810|editor1-last=Warrant|editor1-first=Eric}}</ref> |
|||
===Magnetic fields=== |
|||
The perception of magnetic fields by migratory birds has been suggested to be light dependent.<ref>{{cite journal|title=Night-vision brain area in migratory songbirds|journal=PNAS|year=2005|volume=102|pages=8339–8344|doi=10.1073/pnas.0409575102|author=Mouritsen, Henrik; Gesa Feenders, Miriam Liedvogel, Kazuhiro Wada, and Erich D. Jarvis|pmid=15928090|issue=23|pmc=1149410}}</ref> Birds move their head to detect the orientation of the magnetic field,<ref>{{cite journal|title=Migratory birds use head scans to detect the direction of the Earth's magnetic field|journal=Current Biology|volume=14|issue=21|pages= 1946–1949|last=Mouritsen|first=H.|year=2004|doi=10.1016/j.cub.2004.10.025|url=http://www.seaturtle.org/PDF/Mouritsen_2004_CurrBiol.pdf|pmid=15530397|last2=Feenders|first2=G|last3=Liedvogel|first3=M|last4=Kropp|first4=W}}</ref> and studies on the neural pathways have suggested that birds may be able to "see" the magnetic fields.<ref>{{cite journal|author=Heyers D, Manns M, Luksch H, Güntürkün O, Mouritsen H|year=2007|title=A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds|journal=PLoS ONE |volume=2 |issue=9 |page=e937 |doi=10.1371/journal.pone.0000937|pmid=17895978|pmc=1976598|editor1-last=Iwaniuk|editor1-first=Andrew}}</ref> The right eye of a migratory bird contains photoreceptive proteins called [[cryptochrome]]s. Light excites these molecules to produce unpaired electrons that interact with the Earth's magnetic field, thus providing directional information.<ref name= shanor>{{cite book| last = Shanor | first = Karen | coauthors=Kanwal, Jagmeet | title =Bats sing, mice giggle: revealing the secret lives of animals | year = 2009 | publisher = Icon Books | isbn =1-84831-071-4 |page = 25}} (Despite its title, this is written by professional scientists with many references)</ref><ref> |
|||
{{cite journal |
|||
| last = Heyers |
|||
| first = Dominik |
|||
| title = A Visual Pathway Links Brain Structures Active during Magnetic Compass Orientation in Migratory Birds |
|||
| journal = PLoS ONE |
|||
| volume = 2 |
|||
| issue = 9 |
|||
| pages = e937 |
|||
| month = September | year = 2007 |
|||
| doi =10.1371/journal.pone.0000937 |
|||
| url = http://www.plosone.org/article/fetchArticle.action?articleURI=info:doi/10.1371/journal.pone.0000937 |
|||
| accessdate = 2007-09-27 |
|||
| pmid = 17895978 |
|||
| last2 = Manns |
|||
| first2 = M |
|||
| last3 = Luksch |
|||
| first3 = H |
|||
| last4 = Güntürkün |
|||
| first4 = O |
|||
| last5 = Mouritsen |
|||
| first5 = H |
|||
| pmc = 1976598 |
|||
| last6 = Iwaniuk |
|||
| first6 = Andrew |
|||
| editor1-last = Iwaniuk |
|||
| editor1-first = Andrew |
|||
}} |
|||
</ref> |
|||
==Variations across bird groups== |
|||
===Diurnal birds of prey=== |
|||
[[File:Hawk eye.jpg|thumb|"Hawk-eyed" is a byword for visual acuity]] |
|||
The visual ability of birds of prey is legendary, and the keenness of their eyesight is due to a variety of factors. Raptors have large eyes for their size, 1.4 times greater than the average for birds of the same weight,<ref name= "brooke"/> and the eye is tube-shaped to produce a larger retinal image. The retina has a large number of receptors per square millimetre, which determines the degree of visual acuity. The more receptors an animal has, the higher its ability to distinguish individual objects at a distance, especially when, as in raptors, each receptor is typically attached to a single ganglion.<ref name= "Sturkie"/> Many raptors have foveas with far more rods and cones than the human fovea (65,000/mm<sup>2</sup> in American Kestrel, 38,000 in humans) and this provides these birds with spectacular long distance vision. The fovea itself can also be lens-shaped, increasing the effective density of receptors further. This combination of factors gives ''[[Buteo]]'' buzzards distance vision 6 to 8 times better than humans.{{Citation needed|date=December 2011}} |
|||
[[File:Chileaneagleretina.svg|thumb|left|Each retina of the [[Black-chested Buzzard-eagle]] has two fovea<ref name=retina>Schematic diagram of retina of right eye, loosely based on Sturkie (1998) 6</ref>]] |
|||
The forward-facing eyes of a bird of prey give binocular vision, which is assisted by a double fovea.<ref name= "Sinclair"/> The raptor's adaptations for optimum visual resolution (an [[American Kestrel]] can see a 2–mm insect from the top of an 18–m tree) has a disadvantage in that its vision is poor in low light level, and it must roost at night.<ref name= "Sturkie"/> Raptors may have to pursue mobile prey in the lower part of their visual field, and therefore do not have the lower field myopia adaptation demonstrated by many other birds.<ref name= "Sturkie"/> Scavenging birds like [[vulture]]s do not need such sharp vision, so a [[condor]] has only a single fovea with about 35,000 receptors mm<sup>2</sup> |
|||
Raptors lack coloured oil drops in the cones, and probably have similar colour perception to humans, and lack the ability to detect polarised light. The generally brown, grey and white plumage of this group, and the absence of colour displays in courtship suggests that colour is relatively unimportant to these birds.<ref name= "Sinclair"/> |
|||
In most raptors a prominent eye ridge and its feathers extends above and in front of the eye. This "eyebrow" gives birds of prey their distinctive stare. The ridge physically protects the eye from wind, dust, and debris and shields it from excessive glare. The [[Osprey]] lacks this ridge, although the arrangement of the feathers above its eyes serves a similar function; it also possesses dark feathers in front of the eye which probably serve to reduce the glare from the water surface when the bird is hunting for its staple diet of fish.<ref name= "Jones"/> |
|||
===Nocturnal birds=== |
|||
[[File:Eagle Owl IMG 9203.JPG|thumb|[[Eurasian Eagle-owl]]]] |
|||
Owls have very large eyes for their size, 2.2 times greater than the average for birds of the same weight,<ref name= "brooke"/> and positioned at the front of the head. The eyes have a field overlap of 50–70%, giving better [[binocular vision]] than for diurnal birds of prey (overlap 30–50%).<ref name= "Burton">Burton (1985) 44–48</ref> The Tawny Owl's [[retina]] has about 56,000 light-sensitive [[rod cell|rods]] per square millimetre (36 million per square inch); although earlier claims that it could see in the [[infrared]] part of the [[Electromagnetic spectrum|spectrum]] have been dismissed.<ref name= "Hecht" >{{cite journal|last=Hecht |first=Selig |year=1940 |title=THE SENSIBILITY OF THE NOCTURNAL LONG-EARED OWL IN THE SPECTRUM|url=http://www.jgp.org/cgi/reprint/23/6/709|format=Automatic PDF download |journal=Journal of General Physiology |volume=23 |pages=709–717 |doi=10.1085/jgp.23.6.709 |pmid=19873186 |pmc=2237955 |issue=6|last2=Pirenne|first2=MH}}</ref> |
|||
[[File:Owlretina.svg|left|thumb|Each owl's retina has a single fovea<ref name=retina/>]] |
|||
Adaptations to night vision include the large size of the eye, its tubular shape, large numbers of closely packed retinal rods, and an absence of cones, since colour vision is unnecessary at night. There are few coloured oil drops, which would reduce the light intensity, but the retina contains a reflective layer, the [[tapetum lucidum]]. This increases the amount of light each photosensitive cell receives, allowing the bird to see better in low light conditions.<ref name = "Sinclair"/> Owls normally have only one fovea, and that is poorly developed except in diurnal hunters like the [[Short-eared Owl]].<ref name ="Burton"/> |
|||
Besides owls, [[Bat Hawk|bat hawks]], [[frogmouths]] and [[nightjars]] also display good night vision. Some bird species nest deep in cave systems which are too dark for vision, and find their way to the nest with a simple form of [[Animal echolocation|echolocation]]. The [[Oilbird]] is the only nocturnal bird to echolocate,<ref name= "Cleere" >{{cite book|last=Cleere |first=Nigel |coauthors=Nurney, David |title=Nightjars: A Guide to the Nightjars, Frogmouths, Potoos, Oilbird and Owlet-nightjars of the World |year= 1998|publisher=Pica / Christopher Helm |isbn=1-873403-48-8 |pages=7|oclc=39882046}}</ref> but several ''[[Aerodramus]]'' swiftlets also utilise this technique, with one species, [[Atiu Swiftlet]], also using echolocation outside its caves.<ref name= "Fullard" >{{cite journal|last=Fullard |first=J. H.|month= |year=1993 |title=Echolocation in free-flying Atiu Swiftlets (''Aerodramus sawtelli'') |journal=Biotropica |volume=25 |issue= 3|pages=334–339|url=http://www.erin.utoronto.ca/%7Ew3full/reprints/1993FullBarcThomKopekaBiotropica.pdf |format=PDF |doi=10.2307/2388791| quotes = |accessdate=12 July 2008|first2=.|author3=Thomas|last2=Barclay|jstor=2388791 }}</ref><ref name= "Konishi" >{{cite journal|last=Konishi |first=M. |month=April |year=1979 |title=The oilbird: hearing and echolocation |journal=Science |volume=204 |issue= 4391|pages=425–427|url= |format= |doi= 10.1126/science.441731| pmid = 441731 |quotes = |last2=Knudsen|first2=EI }}</ref> |
|||
===Water birds=== |
|||
[[File:Crested tern444 edit.jpg|thumb|Terns have coloured oil droplets in the cones of the eye to improve distance vision]] |
|||
Seabirds such as [[tern]]s and [[gull]]s that feed at the surface or plunge for food have red oil droplets in the [[cone (eye)|cones]] of their [[retina]]s. This improves contrast and sharpens distance vision, especially in hazy conditions.<ref name= "Sinclair"/> Birds that have to look through an air/water interface have more deeply coloured [[carotenoid]] [[pigment]]s in the oil drops than other species.<ref name = "Varela">Varela, F. J.; Palacios, A. G.; Goldsmith T. M. "Color vision in birds" in Ziegler & Bischof (1993) 77–94</ref> |
|||
This helps them to locate shoals of fish, although it is uncertain whether they are sighting the [[phytoplankton]] on which the fish feed, or other feeding birds.<ref name= "Lythgoe">{{cite book|last=Lythgoe |first=J. N.|coauthors= |title=The Ecology of Vision |year=1979 |publisher=Oxford: Clarendon Press |isbn=0-19-854529-0 |pages=180–183|oclc=4804801}}</ref> |
|||
Birds that fish by stealth from above the water have to correct for refraction particularly when the fish are observed at an angle. [[Reef Heron]]s and [[Little Egret]]s appear to be able to make the corrections needed when capturing fish and are more successful in catching fish when strikes are made at an acute angle and this higher success may be due to the inability of the fish to detect their predators.<ref>{{cite journal|journal=Anim. Behav.|year=1991|volume=42|pages=341–346|title=Capture of submerged prey by little egrets, ''Egretta garzetta garzetta'': strike depth, strike angle and the problem of light refraction|url=http://www.tau.ac.il/~lotem/Lotem%20et%20al%2091%20AnimBehav.pdf|format=pdf|author=Lotem A, Schechtman E & G Katzir|doi=10.1016/S0003-3472(05)80033-8|issue=3}}</ref> |
|||
Birds that pursue fish under water like [[auk]]s and [[loon|divers]] have far fewer red oil droplets,<ref name ="Sinclair"/> but they have special flexible lenses and use the nictitating membrane as an additional lens. This allows greater optical accommodation for good vision in air and water.<ref name = "Gill"/> Cormorants have a greater range of visual [[accommodation (eye)|accommodation]], at 50 [[dioptre]]s, than any other bird, but the kingfishers are considered to have the best all-round (air and water) vision.<ref name ="Sinclair"/> |
|||
[[File:Manxshearwaterretina.svg|thumb|left|Each retina of the Manx Shearwater has one fovea and an elongated strip of high photoreceptor density<ref name =retina/>]] |
|||
[[Procellariiformes|Tubenosed]] seabirds, which come ashore only to breed and spend most of their life wandering close to the surface of the oceans, have a long narrow area of visual sensitivity on the retina<ref name ="Sturkie"/> This region, the ''area giganto cellularis'', has been found in the [[Manx Shearwater]], [[Kerguelen Petrel]], [[Great Shearwater]], [[Broad-billed Prion]] and [[Common Diving-petrel]]. It is characterised by the presence of ganglion cells which are regularly arrayed and larger than those found in the rest of the retina, and morphologically appear similar to the cells of the retina in [[cat]]s. The location and cellular morphology of this novel area suggests a function in the detection of items in a small binocular field projecting below and around the bill. It is not concerned primarily with high spatial resolution, but may assist in the detection of prey near the sea surface as a bird flies low over it.<ref name= "Hayes">{{cite journal|last=Hayes |first=Brian |month= |year=1991 |title=Novel area serving binocular vision in the retinae of procellariiform seabirds |journal=Brain, Behavior and Evolution |volume=37 |issue=2|pages=79–84 |url= |format= |doi=10.1159/000114348|last2=Martin|first2=Graham R.|last3=Brooke|first3=Michael de L.}}</ref> |
|||
The [[Manx Shearwater]], like many other seabirds, visits its breeding colonies at night to reduce the chances of attack by aerial predators. Two aspects of its optical structure suggest that the eye of this species is adapted to vision at night. In the shearwater's eyes the lens does most of the bending of light necessary to produce a focused image on the retina. The cornea, the outer covering of the eye, is relative flat and so of low [[refraction|refractive]] power. In a diurnal bird like the pigeon, the reverse is true; the cornea is highly curved and is the principal refractive component. The ration of refraction by the lens to that by the cornea is 1.6 for the shearwater and 0.4 for the pigeon; the figure for the shearwater is consistent with that for a range of different nocturnal bird and mammal.<ref name= "Martinbrooke"/> |
|||
The shorter focal length of shearwater eyes give them a smaller, but brighter, image than is the case for pigeons, so the latter has sharper daytime vision. Although the Manx Shearwater has adaptations for night vision, the effect is small, and it is likely that these birds also use smell and hearing to locate their nests.<ref name= "Martinbrooke">{{cite journal|last=Martin |first=Graham R.|month= |year=1991 |title=The Eye of a Procellariiform Seabird, the Manx Shearwater, ''Puffinus puffinus'': Visual Fields and Optical Structure |journal=Brain, Behaviour and Evolution|volume=37 |issue=2|pages=65–78 |doi=10.1159/000114347|last2=Brooke|first2=M. de L. }}</ref> |
|||
It used to be thought that [[penguin]]s were short-sighted on land. Although the cornea is flat and adapted to swimming underwater, the lens is very strong and can compensate for the reduced corneal focusing when out of water.<ref name ="Burton"/> Almost the opposite solution is used by the [[Hooded Merganser]] which can bulge part of the lens through the iris when submerged.<ref name ="Burton"/> |
|||
--> |
--> |
||
Revisi per 15 Juni 2012 04.44
 | Artikel ini perlu diterjemahkan dari bahasa Inggris ke bahasa Indonesia. Artikel ini ditulis atau diterjemahkan secara buruk dari Wikipedia bahasa Inggris. Jika halaman ini ditujukan untuk komunitas bahasa Inggris, halaman itu harus dikontribusikan ke Wikipedia bahasa Inggris. Lihat daftar bahasa Wikipedia. Artikel yang tidak diterjemahkan dapat dihapus secara cepat sesuai kriteria A2. Jika Anda ingin memeriksa artikel ini, Anda boleh menggunakan mesin penerjemah. Namun ingat, mohon tidak menyalin hasil terjemahan tersebut ke artikel, karena umumnya merupakan terjemahan berkualitas rendah. |
 | Artikel ini sebatang kara, artinya tidak ada artikel lain yang memiliki pranala balik ke halaman ini. Bantulah menambah pranala ke artikel ini dari artikel yang berhubungan atau coba peralatan pencari pranala. |
Penglihatan adalah indra yang paling penting untuk burung, karena penglihatan yang baik sangat penting bagi penerbangan yang aman, dan kelompok burung memiliki sejumlah adaptasi yang memberikan ketajaman visual dari kelompok vertebrata lainnya; merpati dideskripsikan sebagai "dua mata dengan sayap".[1] Mata burung mirip dengan reptil, dengan otot silia yang dapat mengubah bentuk lensa mata dengan cepat dan bertaraf lebih tinggi daripada mamalia. Burung memiliki mata relatif besar untuk seukuran mereka dalam kingdom animalia, dan akibatnya gerakannya terbatasi oleh tulang rongga mata.[1] Selain kedua kelopak mata yang biasanya ditemukan pada vertebrata, mata burung juga dilindungi oleh membran ketiga yang transparan dan dapat digerakkan. Anatomi internal mata burung sama dengan vertebrata lain, namun memiliki struktur tambahan, pekten okuli, yang hanya ada pada burung.
Penglihatan burung tidak seprti manusia, tapi sama dengan ikan, amfibia dan reptil, yang mempunyai empat jenis reseptor warna di mata. Ini memberikan burung kemampuan untuk memahami tidak hanya kisaran yang terlihat tetapi juga bagian ultraviolet dari spektrum, dan adaptasi lain yang memungkinkan untuk mendeteksi cahaya terpolarisasi atau medan magnet. Burung memiliki reseptor yang lebih terang secara proposional di retina daripada mamalia, dan koneksi saraf lebih banyak antara fotoreseptor dan otak.
Beberapa jenis burung memiliki modifikasi khusus untuk sistem visual mereka terkait dengan cara hidup mereka. Burung pemangsa memiliki reseptor dengan kepadatan tinggi dan adaptasi lain yang memaksimalkan ketajaman visual. Penempatan mata mereka memberi mereka penglihatan binokular yang baik yang memungkinkan penilaian akurat berdasarkan jarak. Spesies nokturnal mempunyai mata berbentuk tabung, detektor warna dengan jumlah sedikit, tetapi memiliki sel batang dengan kepadatan tinggi yang berfungsi baik saat cahaya sedikit. Dara laut, camar dan albatros adalah satu dari burung laut yang memiliki tetesan minyak merah atau kuning pada reseptor warna untuk memperbaiki penglihatan jarak terutama pada kondisi berkabut.
Anatomi ekstraokular
Mata burung paling dekat menyerupai mata reptil. Ia tidak mirip dengan mata mamalia, matanya tidak bulat, dan bentuk datar memungkinkan lebih bidang visual untuk menjadi fokus. Lingkaran lempengan tulang, yaitu cincin sklerotik, mengelilingi mata membuat mata menjadi kaku. tetapi sebuah perbaikan dalam mata reptil, ditemukan juga di mamalia, yakni lensa matanya lebih menonjol kedepan, sehingga meningkatkan jumlah bayangan objek yang jatuh ke retina.[2]
Kebanyakan burung tidak bisa menggerakkan matanya, meski ada beberapa pengecualian, seperti burung Dendang Air.[3] Burung dengan mata yang terletak di kedua sisi kepala memiliki bidang pandang yang luas, hal ini berguna untuk mendeteksi adanya pemangsa, sementara burung dengan mata di depan kepala seperti burung hantu memiliki daya penglihatan binokular, sehingga mampu memperkirakan jarak pada saat berburu.[4] Berkik-gunung amerika mungkin memiliki bidang visual terbesar dari burung apapun, 360° pada bidang horisontal, dan 180° pada bidang vertikal.[5]
Kelopak mata burung tidak digunakan untuk berkedip. Mata burung mendapat pelumasan dari membran pengelip, kelopak mata ketiga yang tersembunyi yang mengusap kearah horisontal keseluruh mata seperti pembersih kaca.[6] Membran pengelip juga menutup mata sepeti lensa kontak pada burung air pada saat mereka menyelam.[7] Saat tidur, pada kebanyaka burung kelopak mata bawah terangkat keatas untuk menutup mata, kecuali burung hantu bertanduk dimana kelopak mata atas yang bergerak.[8] Mata juga dibersihkan dengan cairan air mata dari kelenjar air mata dan dilindungi oleh zat berminyak dari kelenjar Harderian yang melapisi kornea dan mencegah kekeringan. Mata burung lebih besar dibandingkan dengan ukuran hewan daripada kelompok hewan lain, meskipun sebagian besar yang tersembunyi dalam tengkorak. Burung unta memiliki mata terbesar dari vertebrata darat, dengan panjang aksial 50 mm, dua kali lipat dari mata manusia.[1]
Ukuran mata burung terkait erat dengan massa tubuhnya. Sebuah studi dari lima jenis burung(burung beo, merpati, petrel, burung pemangsa dan burung hantu) menunjukkan bahwa massa mata sebanding dengan massa tubuh, tapi seperti yang diharapkan dari kebiasaan mereka dan ekologi visualnya, burung laut dan burung hantu memiliki mata yang relatif besar untuk ukuran massa tubuh mereka.[9] Studi tentang perilaku burung menunjukkan bahwa banyak spesies burung fokus pada objek yang jauh memiliki keistimewaan pada daya penglihatan lateral dan monokular, dan burung akan mengorientasikan diri ke samping untuk memaksimalkan resolusi visual. Untuk seekor merpati, pandangan kesamping memiliki resolusi dua kali lebih baik dari pada pandangan ke depan, sedangkan bagi manusia terjadi hal yang sebaliknya.[1]
Kinerja mata dalam tingkat cahaya rendah tergantung pada jarak antara lensa dan retina, dan burung kecil secara efektif dipaksa menjadi burung siang karena mata mereka tidak cukup besar untuk melihat diwaktu malam. Meskipun banyak spesies bermigrasi di malam hari, mereka sering berbenturan dengan bermacam objek bahkan objek yang terang benderang seperti mercusuar atau platform pengeboran minyak. Burung pemangsa adalah burung siang, karena meskipun mata mereka besar, namun mata tersebut dioptimalkan untuk memberikan resolusi spasial yang maksimum, sehingga mata tersebut juga tidak berfungsi dengan baik dalam cahaya yang buruk.[10] Banyak burung memiliki struktur mata yang asimetri, yang memungkinkan mereka untuk fokus pada cakrawala dan bagian penting dari tanah secara bersamaan. Adaptasi ini dimungkinkan karena burung memiliki miopia di bagian bawah bidang pandang mereka.[1] Burung dengan mata yang relatif besar dibandingkan dengan massa tubuh mereka, seperti Redstart dan Robin Eropa akan menyanyi sebelum fajar sebelum burung-burung dengan ukuran yang sama dan massa tubuh yang lebih kecil. Namun, jika burung memiliki ukuran mata yang sama tetapi massa tubuh yang berbeda, spesies yang lebih besar menyanyikan lebih lambat dibanding spesies yang lebih kecil. Ini mungkin karena burung kecil harus memulai hari lebih awal karena pengurangan berat badan semalam.[11] Burung malam memiliki mata yang sangat optimal terhadap sensitivitas visual, dengan kornea yang relatif besar terhadap panjang mata, sedangkan burung siang memiliki mata yang relatif panjang terhadap diameter kornea untuk memberikan ketajaman visual yang lebih besar. Informasi tentang spesies yang sudah punah dapat disimpulkan dari pengukuran dari cincin sklerotik dan kedalaman orbit. Agar pengukuran bisa dilakukan, fosil tersebut harus masih memiliki benuk tiga dimensi. Untuk spesimen datar seperti Archeopteryx, pengukuran tidak bisa dilakukan karna meskipun memiliki cincin sklerotik lengkap tetapi tidak ada pengukuran kedalaman orbit.[12]
Anatomi mata
Struktur utama dari mata burung mirip dengan vertebrata lainnya. Lapisan luar mata terdiri dari kornea transparan di bagian depan, dan dua lapisan sklera - lapisan serat kolagen kuat berwarna putih yang mengelilingi seluruh mata dan mendukung dan melindungi mata secara keseluruhan. Mata ini dibagi secara internal oleh lensa menjadi dua bagian utama: bagian anterior dan bagian posterior. Ruang anterior berisi cairan yang disebut aqueous humor, dan ruang posterior berisi vitreous humor, suatu zat bening seperti jeli.
Lensa merupakan bagian transparan yang berbentuk cembung dengan lapisan keras di bagian luar dan lapisan dalam yang lebih lembut. Lensa berfungsi memfokuskan cahaya pada retina. Bentuk lensa dapat diubah oleh otot-otot siliari yang langsung melekat pada lensa melalui serat zonular. Selain otot-otot ini, beberapa burung juga memiliki otot Crampton, yang dapat mengubah bentuk kornea, sehingga memberikan burung rentang pandang yang lebih besar dibandingkan mamalia yang lain. Perubahan ini dapat dilakukan dengan cepat untuk beberapa jenis burung air yang bisa menyelam. Iris adalah diafragma muskular yang berwarna terletak di depan lensa yang mengontrol jumlah cahaya yang masuk mata. Di tengah-tengah iris terdapat pupil, daerah lingkaran variabel yang dilalui cahaya untuk masuk ke dalam mata.[2][13]
Retina adalah bagian yang yang memiliki banyak lapisan melengkung dan lembut, yang memiliki sel fotoreseptor rods dan cones yang terhubung ke neuron dan pembuluh darah. Kepadatan fotoreseptor sangat penting dalam menentukan pencapaian ketajaman visual maksimum. Manusia memiliki sekitar 200.000 reseptor per mm², tetapi burung Sparrow memiliki 400.000 reseptor per mm² dan Elang Buteo memiliki 1.000.000 reseptor per mm². Tidak semua fotoreseptor terhubung ke saraf optik secara individual, dan rasio saraf ganglion pada reseptor cukup penting dalam menentukan resolusi. Untuk burung, rasio ini sangat tinggi, burung Wagtail Putih memiliki sel ganglion 100.000 hingga 120.000 fotoreseptor.[2]
Sel fotoreseptor rods lebih sensitif terhadap cahaya, tetapi tidak memberikan informasi warna, sedangkan sel fotoreseptor cones kurang sensitif terhadap cahaya namun memungkinkan penglihatan yang berwarna. Pada burung siang, 80% dari reseptor adalah sel fotoreseptor cones (90% untuk beberapa burung walet) sedangkan burung hantu memiliki hampir semua sel fotoreseptor rods . Seperti vertebrata lainnya kecuali mamalia plasenta, beberapa sel fotoreseptor cones memiliki struktur ganda, dan jumlah ini dapat mencapai 50% dari semua sel fotoreseptor cones pada beberapa spesies.[14]
Di bagian tengah retina adalah fovea yang memiliki kepadatan yang lebih besar dari reseptor dan merupakan daerah ketajaman visual kedepan yang terbesar, (paling tajam, dapat mendeteksi objek paling jelas). Dalam 54% burung, termasuk burung pemangsa, raja-udang, kolibri dan burung layang-layang, memiliki fovea kedua untuk meningkatkan penglihatan ke samping. Saraf optik adalah kumpulan serabut saraf yang membawa pesan dari mata ke bagian yang relevan di otak dan sebaliknya. Seperti mamalia, burung memiliki daerah buta kecil yang tidak memiliki fotoreseptor, di daerah di mana mata digabungkan oleh saraf optik dan pembuluh darah.[2]
Pekten adalah bagian yang masih kurang dipahami, yang terdiri dari jaringan lipat yang terhubung ke retina. Pekten juga memiliki banyak pembuluh darah dan menjaga retina dari kekurangan pasokan nutrisi,[1] dan juga dapat melindungi retina dari cahaya yang menyilaukan atau membantu mendeteksi benda bergerak.[2]
Koroid adalah lapisan yang terletak di belakang retina yang berisi pembuluh nadi kecil dan pembuluh balik yang mengalirkan darah ke retina. Koroid mengandung melanin, pigmen yang memberikan warna gelap pada mata, membantu untuk mencegah gangguan dari refleksi.
Referensi
- ^ a b c d e f Güntürkün, Onur, "Structure and functions of the eye" in Sturkie (1998) 1–18
- ^ a b c d e Sinclair (1985) 88–100
- ^ White, Craig R.; Day, N; Butler, PJ; Martin, GR; Bennett, Peter (2007). Bennett, Peter, ed. "Vision and Foraging in Cormorants: More like Herons than Hawks?" (PDF). PLoS ONE. 2 (7): e639. doi:10.1371/journal.pone.0000639. PMC 1919429
. PMID 17653266.
- ^ Martin, Graham R.; Katzir, G (1999). "Visual fields in short-toed eagles, Circaetus gallicus (Accipitridae), and the function of binocularity in birds". Brain, Behaviour and Evolution. 53 (2): 55–66. doi:10.1159/000006582. PMID 9933782.
- ^ Jones, Michael P; Pierce Jr, Kenneth E.; Ward, Daniel (2007). "Avian vision: a review of form and function with special consideration to birds of prey" (PDF). Journal of Exotic Pet Medicine. 16 (2): 69–87. doi:10.1053/j.jepm.2007.03.012.
- ^ Williams, David L.; Flach, E (2003). "Symblepharon with aberrant protrusion of the nictitating membrane in the snowy owl (Nyctea scandiaca)" (PDF). Veterinary Ophthalmology. 6 (1): 11–13. doi:10.1046/j.1463-5224.2003.00250.x. PMID 12641836.
- ^ Gill, Frank (1995). Ornithology. New York: WH Freeman and Co. ISBN 0-7167-2415-4. OCLC 30354617.
- ^ The bird: its form and function. Henry Holt & Co, New York. 1906. hlm. 214.
- ^ Brooke, M. de L.; Hanley, S.; Laughlin, S. B. (1999). "The scaling of eye size with body mass in birds". Proceeding of the Royal Society Biological Sciences. 266 (1417): 405–412. doi:10.1098/rspb.1999.0652. PMC 1689681 .
- ^ Martin, Graham. "Producing the image" in Ziegler & Bischof (1993) 5–24
- ^ Thomas, Robert J.; Suzuki, M; Saito, S; Tanda, S; Newson, Stuart E.; Frayling, Tim D.; Wallis, Paul D. (2002). "Eye size in birds and the timing of song at dawn". Proceedings of the Royal society of London. 269 (1493): 831–837. doi:10.1098/rspb.2001.1941. PMC 1690967 . PMID 11958715.
- ^ Hall, Margaret I. (2008). "The anatomical relationships between the avian eye, orbit and sclerotic ring: implications for inferring activity patterns in extinct birds". Journal of Anatomy. 212 (6): 781–794. doi:10.1111/j.1469-7580.2008.00897.x. PMC 2423400 . PMID 18510506.
- ^ Sivak, Jacob G. (2004). "Through the Lens Clearly: Phylogeny and Development". Invest. Ophthalmol. Vis. Sci. 45 (3): 740–747. doi:10.1167/iovs.03-0466. PMID 14985284.
- ^ Nalbach Hans-Ortwin; Wolf-Oberhollenzer, Friedericke; Remy Monika. "Exploring the image" in Ziegler & Bischof (1993) 26–28
 | Artikel bertopik burung ini adalah sebuah rintisan. Anda dapat membantu Wikipedia dengan mengembangkannya. |