Liz,
Ari and
Biker, many thanks!
Pica
Ari19 wrote: ↑August 15th, 2019, 5:59 pm
Wow, Anne7! That is such an amount!
One issue though... I’m afraid I won’t be able to tell if the article I want to post is already here. How will we prevent doubles?
Yes, Ari, it becomes hard to see if we don't post the same article twice.
What I do when I have doubts: I copy part of the new title (keywords) and paste it (between " " ) in the search tool (on top at the right).
If the same article has already been posted, it will be found this way.
Once everything will be arranged according to their theme, the checking on "doubles" will probably be easier.
Research into Bird Migration
Posted here: viewtopic.php?p=622836#p622836
Wind blows young migrant birds to all corners of Africa
University of Amsterdam
Migrant birds that breed in the same area in Europe spread out across all of Africa during the northern winter. A new satellite-tracking study shows that
the destination of individual birds is largely determined by the wind conditions they encounter during their first migration. The results were made available open access in the peer-reviewed journal Proceedings of the Royal Society B.
https://phys.org/news/2017-05-young-mig ... .html#nRlv
Posted here: viewtopic.php?p=622836#p622836
Migratory Birds May Come Programmed With a Genetic Google Maps
These hybrid avians inherit some mixed directional messages
Many young birds migrate successfully without help from older birds who have made the trip before. The implication is that migration instructions - perhaps even some sort of map of astronomical or geographical references - are somehow written upon the genes inherited from their parents. Just how maps can be coded into gene structure is anyone's guess. In fact, since the DNA in the genes seems to code only for protein synthesis, the locations and characters of inheritable maps are still not understood.
For example, the Swainson’s thrush is split into two subgroups that migrate along very different routes. Every spring both subgroups return to Canada and— here’s the key —
they sometimes interbreed.
The researchers found that
the 'hybrid' offspring favoured a flyway that was in between those of the two subgroups! Since the hybrid thrushes couldn’t have learned that middle road, it seems that the birds were guided by a mixture of genetic instructions inherited from both parents.
Read more:
https://www.smithsonianmag.com/science- ... iuc2rPB.99
Posted here: viewtopic.php?p=622836#p622836
Mixed genes mix up the migrations of 'hybrid' birds
Researcher Kira Delmore
Mixed genes appear to drive hybrid birds to select more difficult routes than their parent species, according to new research from University of British Columbia zoologists. “Instead of taking well-trodden paths through fertile areas, these birds choose to scale mountains and cross deserts,” says UBC researcher Kira Delmore.
https://news.ubc.ca/2014/07/22/mixed-ge ... rid-birds/
Posted here: viewtopic.php?p=618022#p618022
Air speeds of migrating birds observed by ornithodolite and compared with predictions from flight theory
C. J. Pennycuick , Susanne Åkesson and Anders Hedenström
Abstract:
We measured the air speeds of 31 bird species, for which we had body mass and wing measurements, migrating along the east coast of Sweden in autumn, using a Vectronix Vector 21 ornithodolite and a Gill WindSonic anemometer. We expected each species’ average air speed to exceed its calculated minimum-power speed (Vmp), and to fall below its maximum-range speed (Vmr), but found some exceptions to both limits. To resolve these discrepancies, we first reduced the assumed induced power factor for all species from 1.2 to 0.9, attributing this to splayed and up-turned primary feathers, and then assigned body drag coefficients for different species down to 0.060 for small waders, and up to 0.12 for the mute swan, in the Reynolds number range 25 000–250 000. These results will be used to amend the default values in existing software that estimates fuel consumption in migration, energy heights on arrival and other aspects of flight performance, using classical aeronautical theory. The body drag coefficients are central to range calculations. Although they cannot be measured on dead bird bodies, they could be checked against wind tunnel measurements on living birds, using existing methods.
"... Usually, as thermals do not form over water, birds fly low above the water. ..."
"... Figure 2 shows that the average flying height was less than 50m above the water surface in all 31 species in our sample, and less than 10m in 16 of them. ... As most (observed) tracks were several hundred metres long, these low flying heights constrained the flight paths to be nearly horizontal, as assumed by the theory. ..."
Mean flying heights above the water surface for 31 species in our sample
https://royalsocietypublishing.org/doi/ ... .2013.0419
Avian navigation: from historical to modern concepts
ROSWITHA WILTSCHKO & WOLFGANG WILTSCHKO
© 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved
Studies on avian navigation began at the end of the 19th century with testing various hypotheses, followed by large-scale displacement experiments to assess the capacity of the birds’ navigational abilities. In the 1950s, the first theoretical concepts were published. Kramer proposed his ‘Map-and-Compass’model, assuming that birds establish the direction to a distant goal with the help of an external reference, a compass. The model describes homing as a two-step process, with the first step determining the direction to the goal as a compass course and the second step locating this course with the help of a compass. This model was widely accepted when numerous experiments with clock-shifted pigeons demonstrated the use of the sun compass, and thus a general involvement of compass orientation, in homing. The ‘map’ step is assumed to use local site-specific information, which led to the idea of a ‘gridmap’ based on environmental gradients. Kramer’s model still forms the basis of our present concept on avian homing, yet route integration with the help of an external reference provides an alternative strategy to determine the home course, and the magnetic compass is a second compass mechanism available to birds. These mechanisms are interrelated by ontogenetic learning processes. A two-step process, with the first step providing the compass course and the second step locating this course with the help of a compass, appears to be a common feature of avian navigation tasks, yet the origin of the compass courses differs between tasks according to their nature, with
courses acquired by experience for flights within the home range, courses based on navigational processes for returning home, and courses derived from genetically coded information in first-time migrants. Compass orientation thus forms the backbone of the avian navigational system.
https://www.academia.edu/24491372/Avian ... n_concepts
Posted here: viewtopic.php?p=613362#p613362
How Do Birds Migrate Over Thousands Of Kilometers Without Ever Getting Lost?
John Staughton in Science ABC
In many parts of the world, people can look up at certain times of the day and see huge flocks of migrating birds passing overhead. It has been noted by researchers and ornithologists throughout history that birds often take the same migratory paths year after year. Furthermore, many of them return to the exact same locations at either end of their migrations, spots sometimes separated by tens of thousands of miles!
There are about 10,000 bird species in the world, and nearly 20% of them are long-distance migrants. These migratory species typically move in a north-south directional pattern between their “breeding” grounds and their “wintering” grounds. Migration primarily occurs due to the need to reproduce, the availability of food, and increased/decreased threats of predation.
The size of migratory routes can vary widely, from as little as a few hundred meters to well over 50,000 miles. These migratory patterns have been recognized by humans for more than 3,000 years, yet this ability in birds remains an incredibly mysterious skill. Certain conclusions and observations have been made to clue us into this special secret, but there are still a lot of questions. ...
Vision-based magnetoreception
"One of the more complicated theories to explain avian migration involves bird species’ ability to detect the magnetic fields of the Earth, and subsequently follow those fields to their ultimate destination. This ability to use “invisible” waves was hard for some ornithologists to swallow, but it was proposed that some bird beaks contain magnetic particles that act as a compass. Recently, this theory has fallen out of fashion, replaced by the theory of vision-based magnetoreception.
The concept of vision-based magnetoreception means that birds can “see” magnetic fields and align themselves with the direction of the field they want to travel. If a bird is migrating south, it will align with a south-facing magnetic field and be on its way. Experiments in laboratories have actually generated artificial “magnetic south”, and birds moved in that direction. ..."
Simple Avian Eye Diagram (Photo Credit: www.the-scientist.com)
A Quantum Explanation?
"The last great mystery to vision-based magnetoreception is how this sort of magnetic field sensor can be present inside a bird’s retinal cells. One of the most recent theories suggests that quantum mechanics may provide the answer. For such a detector of strength AND direction, some mechanism would need to be in place to amplify the relatively weak magnetic effects of the Earth enough to be detected.
In quantum mechanics, a radical pair consists of two simultaneously created molecules, each with one electron of opposing, associated spin that makes these pairs highly sensitive to outside forces and magnetic fields.
When a specific light-sensitive protein found in the retinal cells of birds, cryptochrome, is exposed to certain wavelengths of green or blue light, it can organically create these radical pairs. Magnetoreception like this is the latest field of quantum biology, and one that is currently being studied around the world."
http://sciabc.us/1cfBR
Lateralization of the Avian Magnetic Compass: Analysis of Its Early Plasticity
Dennis Gehring, Onur Güntürkün, Wolfgang Wiltschko and Roswitha Wiltschko
Academic Editor: Lesley J. Rogers, received 26 March 2017
Abstract: In European Robins, Erithacus rubecula, the magnetic compass is lateralized in favor of the right eye/left hemisphere of the brain. This lateralization develops during the first winter and initially shows a great plasticity. During the first spring migration, it can be temporarily removed by covering the right eye. In the present paper, we used the migratory orientation of robins to analyze the circumstances under which the lateralization can be undone. Already a period of 11/2 h being monocularly left-eyed before tests began proved sufficient to restore the ability to use the left eye for orientation, but this effect was rather short-lived, as lateralization recurred again within the next 11/2 h. Interpretable magnetic information mediated by the left eye was necessary for removing the lateralization. In addition, monocularly, the left eye seeing robins could adjust to magnetic intensities outside the normal functional window, but this ability was not transferred to the “right-eye system”. Our results make it clear that asymmetry of magnetic compass perception is amenable to short-term changes, depending on lateralized stimulation. This could mean that the left hemispheric dominance for the analysis of magnetic compass information depends on lateralized interhemispheric interactions that in young birds can swiftly be altered by environmental effects.
https://www.bio.psy.ruhr-uni-bochum.de/ ... ompass.pdf
Navigation
Roswitha Wiltschko
Journal of Comparative Physiology A
July 2017, Volume 203, Issue 6–7, pp 455–463
Abstract
Experiments with migrating birds displaced during autumn migration outside their normal migration corridor reveal two different navigational strategies: adult migrants compensate for the displacement, and head towards their traditional wintering areas, whereas young first-time migrants continue in their migratory direction.
Young birds are guided to their still unknown goal by a genetically coded migration program that indicates duration and direction(s) of the migratory flight by controlling the amount of migratory restlessness and the compass course(s) with respect to the geomagnetic field and celestial rotation. Adult migrants that have already wintered and are familiar with the goal area approach the goal by true navigation, specifically heading towards it and changing their course correspondingly after displacement. During their first journey, young birds experience the distribution of potential navigational factors en route and in their winter home, which allows them to truly navigate on their next migrations. The navigational factors used appear to include magnetic intensity as a component in their multi-modal navigational ‘map’; olfactory input is also involved, even if it is not yet entirely clear in what way. The mechanisms of migratory birds for true navigation over long distances appear to be in principle similar to those discussed for by homing pigeons.
https://www.researchgate.net/publicatio ... Navigation
Directional orientation of birds by the magnetic field under different light conditions
Roswitha Wiltschko, Katrin Stapput, Peter Thalau and Wolfgang Wiltschko
in Journal of The Royal Society Interface; 7 Suppl 2(Suppl. 2):S163-77 · October 2009
This paper reviews the directional orientation of birds with the help of the geomagnetic fieldunder various light conditions. Two fundamentally different types of response can be distinguished. (i) Compass orientation controlled by the inclination compass that allows birds to locate courses of different origin. This is restricted to a narrow functional window around the total intensity of the local geomagnetic field and requires light from the short-wavelength part of the spectrum. The compass is based on radical-pair processes in the right eye;magnetite-based receptors in the beak are not involved. Compass orientation is observed under ‘white’ and low-level monochromatic light from ultraviolet (UV) to about 565 nm green light. (ii) ‘Fixed direction’ responses occur under artificial light conditions such as more intense monochromatic light, when 590 nm yellow light is added to short-wavelength light, and in total darkness. The manifestation of these responses depends on the ambient light regime and is ‘fixed’ in the sense of not showing the normal change between spring and autumn; their biological significance is unclear. In contrast to compass orientation,fixed-direction responses are polar magnetic responses and occur within a wide range of magnetic intensities. They are disrupted by local anaesthesia of the upper beak, which indicates that the respective magnetic information is mediated by iron-based receptors located there. The influence of light conditions on the two types of response suggests complex interactions between magnetoreceptors in the right eye, those in the upper beak and the visual system.
https://www.researchgate.net/publicatio ... conditions
Resonance effects indicate a radical-pair mechanism for avian magnetic compass
Thorsten Ritz, Peter Thalau, John B. Phillips, Roswitha Wiltschko & Wolfgang Wiltschko
Migratory birds are known to use the geomagnetic field as a source of compass information. There are two competing hypotheses for the primary process underlying the avian magnetic compass, one involving magnetite, the other a magnetically sensitive chemical reaction6–8. Here we show that oscillating magnetic fields disrupt the magnetic orientation behaviour of migratory birds. Robins were disoriented when exposed to a vertically aligned broadband (0.1–10 MHz) or a single-frequency (7-MHz) field in addition to the geomagnetic field. Moreover, in the 7-MHz oscillating field, this effect depended on the angle between the oscillating and the geomagnetic fields. The birds exhibited seasonally appropriate migratory orientation when the oscillating field was parallel to the geomagnetic field, but were disoriented when it was presented at a 248 or 488 angle. These results are consistent with a resonance effect on singlet-triplet transitions and suggest a magnetic compass based on a radical- pair mechanism
https://s3.amazonaws.com/academia.edu.d ... cd2dbc24eb
The evolution of bird migration - A synthesis
Volker Salewski, Bruno Bruderer
Abstract: We approach the problem of the evolution of bird migration by asking whether migration evolves towards new breeding areas or towards survival areas in the non-breeding season. Thus, we avoid the ambiguity of the usually discussed "southern-home-theory" or "northern-home-theory". We argue that migration evolved in birds that spread to seasonal habitats through gradual dispersal to enhance survival during the non-breeding season; this in contrast to the alternative idea suggesting that migration evolved towards new breeding areas to increase reproductive success. Our synthesis is based on the threshold model explaining how migratory traits can change rapidly through microevolutionary processes. Our model brings former theories together and explains
how bird migration, with the appropriate direction and time program, evolves through selection after genetically non-directed events such as dispersal and colonisation. The model does not need the former untested assumptions such as competition as a reason for migration and for the disappearance of sedentary populations or higher reproductive success in temperate breeding areas. Our theory offers answers to questions such as
how birds with a southern origin may gradually reach northern latitudes, why migration routes may follow historical expansion routes and why birds leave an area for the non-breeding season and move back instead of breeding on their wintering grounds. The theory proposes gradual change through selection and not sudden changes such as long distance dispersal or mutations and can be applied to migration at all latitudes and in all directions. The scenario provides a reasonable concept to understand most of the existing migratory phenomena on the basis of the ecology and genetics of migratory behaviour.
https://www.researchgate.net/publicatio ... _synthesis
How do migrating birds find their way?
Ying XIONG, TianLong CAI, FuMin LEI
Abstract: Bird are one of the most abundant and widespread groups in the world. With many specialized structures, such as plumage, air sacs, and hollow bones, most bird species have got flight ability to adapt various niches. Therefore, bird can migrate between wintering and breeding ground, which is usually a long distance, and it’s called migration. Bird navigation is important in migration and is a complex process, which attracts many scientists to dig in how bird finds its way. Since 1873, Charles Darwin has ever mentioned that bird might take the method of dead reckoning on a long-distance migration like human, but at that time no one made further progress. Until 1950s, Kramer firstly found that Common Starling (Sturnus vulgaris) can respond to solar azimuth via mirror test. From then on, many experiments revealed that at least four navigation mechanisms are used in bird migration via more than nine external factors. They are: (i)
celestial navigation, celestial clues (e.g.
solar azimuth,
star position,
and polarized light) are used during migration period. (ii)
Olfactory navigation, odor distributing in the air forms odorous gradient map or mosaic map which can be detected, or can activate directly certain mechanism to navigate. (iii)
Auditory navigation, infrasound (0.05 Hz) produced by mountains and rivers generate sonic gradient map. And (iv)
magnetic navigation, geomagnetic field can be detected via magnetic materials or chemical magnetoreception to find correct directions. Although many scientists approve that magnetic navigation may be the main mechanism to orientate and navigate, bird has never taken just one mechanism to migrate. Indeed, many species also use the other three mechanisms to calibrate direction, for example, Savannah Sparrow (Passerculus sandwichensis) can use polarized light to calibrate the magnetic compass at both sunrise and sunset. Different external clues correspond to different sense organs, so various brain areas should deal with information from different navigation mechanisms. The hippocampus participates in spatial perception and manages anything about celestial navigation via the tectofugal visual pathway and the thalamofugal visual pathway. The piriform cortex (CPi) is the main area to receive stimulation from olfactory bulb and determines how to migrate after receiving olfactory clues. Nervous systems of magnetic navigation include two parts which are trigeminus system and Cluster N. Despite the controversy whether there are some magnetic materials on bird, many experimental evidences have proved that magnetic materials detecting geomagnetic field involve to Trigeminus system. Cluster N, however, is an active area when bird migrates at night and it has an important role in transferring information from chemical magnetoreception to the hippocampus. As illustrated above, navigation mechanisms can get full information from many clues, and then, different brain areas trade off those and co-operate each other to make an elaborate map. Bird navigation involves the receptors to environment and the response of nervous system, so many issues are still maintained. The exact mechanism will be revealed with the new techniques and model animal applied.
http://engine.scichina.com/doi/10.1360/ ... ltextltext
How do migratory birds find their way ?
Biologists on board of the "Alcyon", the boat that undertook an expedition "from the Mediterranean Sea to the Spitzberg", take turns to identify and count all the birds they meet. Among them, many are migratory birds.
It is springtime, that's why! Migratory birds are coming back to cooler areas to breed and build their nest. These birds often make incredible journeys and come back, year after year, to the same place.
http://www.educapoles.org/news/news_det ... _their_way
Wind tunnel as a tool in bird migration research
Anders Hedenström, Åke Lindström
Abstract: Wind tunnels, in which birds fly against an artificially generated air flow, have since long been used to evaluate aerodynamic properties of steady bird flight. A new generation of wind tunnels has also allowed the many processes associated with migratory flights to be studied in captivity. We review how wind tunnel studies of aerodynamics and migratory performance together have helped advancing our understanding of bird migration. Current migration theory is based on the power‐speed relationship of flight as well as flight range equations, both of which can be evaluated using birds flying in wind tunnels. In addition, and depending on wind tunnel properties, performance during gliding and climbing flight, and effects of air pressure, humidity and turbulence on bird flight has been measured. Long‐distance migrant species have been flown repeatedly for up to 16 h non‐stop, allowing detailed studies of the energy expenditure, fuel composition, protein turnover, water balance, immunocompetence and stress associated with sustained migratory flights. In addition, wind tunnels allow the fuelling periods between migratory flights to be studied from new angles. We end our review by suggesting several important topics for future wind tunnel studies, ranging from on of the key questions remaining, the efficiency at which chemical power in converted to mechanical power, to new useful avenues, such as improving and calibrating the techniques used for tracking of individual birds in the wild.
https://onlinelibrary.wiley.com/doi/abs ... /jav.01363
Possible linkage between neuronal recruitment and flight distance in migratory birds
Shay Barkan, Uri Roll, Yoram Yom-Tov, Leonard I. Wassenaar & Anat Barnea
Abstract: New neuronal recruitment in an adult animal’s brain is presumed to contribute to brain plasticity and increase the animal’s ability to contend with new and changing environments. During long-distance migration, birds migrating greater distances are exposed to more diverse spatial information. Thus, we hypothesized that greater migration distance in birds would correlate with the recruitment of new neurons into the brain regions involved with migratory navigation. We tested this hypothesis on two Palearctic migrants - reed warblers (Acrocephalus scirpaceus) and turtle doves (Streptopelia turtur), caught in Israel while returning from Africa in spring and summer. Birds were injected with a neuronal birth marker and later inspected for new neurons in brain regions known to play a role in navigation - the hippocampus and nidopallium caudolateral. We calculated the migration distance of each individual by matching feather isotopic values (δ2H and δ13C) to winter base-maps of these isotopes in Africa. Our findings suggest a positive correlation between migration distance and new neuronal recruitment in two brain regions - the hippocampus in reed warblers and nidopallium caudolateral in turtle doves. This multidisciplinary approach provides new insights into the ability of the avian brain to adapt to different migration challenges.
https://www.nature.com/articles/srep21983
Magnetoreception in Birds and Its Use for Long-Distance Migration
Henrik Mouritsen
Abstract: The Earth’s magnetic field provides potentially useful information, which birds could use for directional and/or positional information. It has been clearly demonstrated that birds are able to sense the compass direction of the Earth’s magnetic field and that they can use this information as part of a compass sense. Magnetic information could also be useful as part of a map sense, and there is a growing body of evidence that birds are able to determine their approximate position on the Earth on the basis of geomagnetic cues. In addition to direct uses for orientation and navigation, magnetic information also seems to be able to influence other physiological processes, such as fattening and migratory motivation, as a trigger for changes in behaviour. Although the behavioural responses to geomagnetic cues are relatively well understood, the physiological mechanisms enabling birds to sense the Earth's magnetic field are only starting to be understood, and understanding the magnetic sense(s) of animals, including birds, remains one of the most significant unsolved problems in biology. It is very challenging to sense magnetic fields as weak as that of the Earth using only biologically available materials. Only two basic mechanisms are considered theoretically viable in terrestrial animals: iron-mineral-based magnetoreception and radical-pair based magnetoreception. On the basis of current scientific evidence, iron-mineral-based magnetoreception and radical-pair-based magnetoreception mechanisms seem to exist in birds, but they seem to be used for different purposes. Plausible primary sensory molecules and a few brain areas involved in processing magnetic information have been identified in birds for each of these two types of magnetic senses. Nevertheless, we are still far away from understanding the detailed function of any of the at least two different magnetic senses existing in some if not all bird species, and, at present, no primary sensory structure has been identified beyond reasonable doubt to be the source of avian magnetoreception. This is an exciting but challenging field in which several major discoveries are likely to be made in the next 1–2 decades.
https://www.researchgate.net/profile/He ... ee284a.pdf
A Model for Photoreceptor-Based Magnetoreception in Birds
Thorsten Ritz, Salih Adem, Klaus Schulten
Abstract: A large variety of animals has the ability to sense the geomagnetic field and utilize it as a source of directional (compass) information. It is not known by which biophysical mechanism this magnetoreception is achieved. We investigate the possibility that magnetoreception involves radical-pair processes that are governed by anisotropic hyperfine coupling between (unpaired) electron and nuclear spins. We will show theoretically that fields of geomagnetic field strength and weaker can produce significantly different reaction yields for different alignments of the radical pairs with the magnetic field. As a model for a magnetic sensory organ we propose a system of radical pairs being 1) orientationally ordered in a molecular substrate and 2) exhibiting changes in the reaction yields that affect the visual transduction pathway. We evaluate three-dimensional visual modulation patterns that can arise from the influence of the geomagnetic field on radical-pair systems. The variations of these patterns with orientation and field strength can furnish the magnetic compass ability of birds with the same characteristics as observed in behavioural experiments. We propose that the recently discovered photoreceptor cryptochrome is part of the magnetoreception system and suggest further studies to prove or disprove this hypothesis.
https://www.sciencedirect.com/science/a ... 950076629X
Long-distance navigation and magnetoreception in migratory animals
Henrik Mouritsen
Naturevolume 558, pages 50–59 (2018)
Abstract:
For centuries, humans have been fascinated by how migratory animals find their way over thousands of kilometres. Here, I review the mechanisms used in animal orientation and navigation with a particular focus on long-distance migrants and magnetoreception. I contend that any long-distance navigational task consists of three phases and that no single cue or mechanism will enable animals to navigate with pinpoint accuracy over thousands of kilometres. Multiscale and multisensory cue integration in the brain is needed. I conclude by raising twenty important mechanistic questions related to long-distance animal navigation that should be solved over the next twenty years.
https://www.nature.com/articles/s41586-018-0176-1
Magnetic compass of migratory Savannah sparrows is calibrated by skylight polarization at sunrise and sunset
Rachel Muheim Æ Susanne A ̊ kesson Æ John B. Phillips
© Dt. Ornithologen-Gesellschaft e.V. 2007
Abstract Migratory birds use compass systems derived from the geomagnetic field, the stars, the sun and polarized light patterns. We tested whether birds use a single underlying reference system for calibration of these compasses and, specifically, whether sunset and sunrise polarized light cues from the region of the sky near the horizon are used to calibrate the magnetic compass. We carried out orientation experiments with Savannah sparrows, Passerculus sandwichensis, in Alaska during autumn migration 2005, and compared the magnetic orientations of individual birds before and after exposure to conflicting information between magnetic and celestial cues. Birds exposed to an artificially shifted polarization pattern (±90° shift relative to the natural condition) for 1 h at local sunrise or sunset recalibrated their magnetic compass, but only when given access to the artificial polarization pattern near the horizon. Birds exposed to a 90° clockwise-shifted magnetic field for 1 h at solar noon did not recalibrate their magnetic compass. These results indicate that migratory birds calibrate their magnetic compass using the skylight polarization pattern vertically intersecting the horizon at sunrise and sunset. In conjunction with earlier work showing that sun and star compass calibrations are secondarily derived from magnetic and polarized light cues, our findings suggest that polarized light cues near the horizon at sunrise and sunset provide the primary calibration reference for the compass systems of migratory songbirds.
https://web.archive.org/web/20081217154 ... 202007.pdf
Posted here: viewtopic.php?p=613362#p613362
How do migratory birds find their way ?
"This question still interests many scientists. It has been shown that birds use several orientation tools.
They can use
the sun, for example, which means that they permanently "know" what time it is, in order to know the right direction on the basis of the sun's position. They are also sensible to the
ultraviolet rays which penetrate the clouds but are invisible for human beings. (So they see the sun's position also on a cloudy day.) Even the nocturnal birds use the position of the sun at sunset to know their position.
Nocturnal birds also use
the stars. This has been proved by letting birds fly in a planetarium and changing the stars' position.
Another tool is the
earth's magnetic field (earth's north and south magnetic poles). Some birds, like pigeons, have a small zone in their brain made of magnetite (magnetic mineral), just like a small compass. But other scientists think it's rather in their eyes that some birds have a system which indicates them where the magnetic north is...
Of course, (experienced) birds also use their knowledge of
the landscape: they follow rivers, valleys or roads, or locate themselves with particular mountain peaks.
Other tracks are still to be explored. For example, it seems that some birds could find their way by following their
sense of smell. ..."
http://www.educapoles.org/news/news_det ... _their_way
Posted here: viewtopic.php?p=613362#p613362
Migrating birds use a magnetic map to travel long distances
"Birds have an impressive ability to navigate. They can fly long distances, to places that they may never have visited before, sometimes returning home after months away.
Though there has been a lot of research in this area, scientists are still trying to understand exactly how they manage to find their intended destinations. ..."
http://theconversation.com/migrating-bi ... nces-82624
Posted here: viewtopic.php?p=613362#p613362
Vision-based magnetoreception
"One of the more complicated theories to explain avian migration involves bird species’ ability to detect the
magnetic fields of the Earth, and subsequently follow those fields to their ultimate destination. This ability to use “invisible” waves was hard for some ornithologists to swallow, but it was proposed that some bird beaks contain magnetic particles that act as a compass. Recently, this theory has fallen out of fashion, replaced by the theory of
vision-based magnetoreception.
The concept of vision-based magnetoreception means that birds can “see” magnetic fields and align themselves with the direction of the field they want to travel.
If a bird is migrating south, it will align with a south-facing magnetic field and be on its way. Experiments in laboratories have actually generated artificial “magnetic south”, and birds moved in that direction. ..."
A Quantum Explanation?
"The last great mystery to vision-based magnetoreception is how this sort of magnetic field sensor can be present inside a bird’s retinal cells. One of the most recent theories suggests that quantum mechanics may provide the answer. For such a detector of strength AND direction, some mechanism would need to be in place to amplify the relatively weak magnetic effects of the Earth enough to be detected.
In quantum mechanics, a radical pair consists of two simultaneously created molecules, each with one electron of opposing, associated spin that makes these pairs highly sensitive to outside forces and magnetic fields.
When a specific light-sensitive protein found in the retinal cells of birds, cryptochrome, is exposed to certain wavelengths of green or blue light, it can organically create these radical pairs.
Magnetoreception like this is the latest field of quantum biology, and one that is currently being studied around the world."
https://www.scienceabc.com/nature/how-m ... field.html
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