How do birds navigate?

Whooping Cranes

       It was not until the sixteenth century that bird migration phenomenon started gaining recognition. Up until then the commonly accepted theory regarding the absence of some bird types during winter season has been attributed to hibernation. Around the year 1600 Pierre Belan, a French ornithologist, conducted an experiment where he had caged some supposedly hibernating birds and watched them throughout the suggested hibernation period [7]. In his experiment, " None ever did. [7]" "Scientific investigation of bird migration began in 1802 when birds were tagged with metal leg bands. [7]" The tagging system helped with tracking the birds throughout the world by recapturing them and reading the information on the tag. Recapturing tagged birds has shown that birds migrate from their nesting home to warmer areas for the winter and return back for the summer. Migration is a necessity for birds' survival for three main reasons: shortage in food, temperature drop and weather conditions during winter time. The tagging system and some other modern tracking techniques have made it possible to observe and draw birds' migration patterns.

      Migration observation has shown that although the general concept of moving to favorable areas is common to all migrating birds, each type has developed some unique route and pace. Some birds do a very short trip like the "…Mountain Quail which breeds at heights up to 3000 m. but winters below 1500 m.. Interestingly, the bird is flightless so it walks up and down the mountains in groups' single file. [7]" In contrast to this short migration distance is the "…record holder in long-distance travel… the Arctic Tern (Sterna Paradisaea), which makes an annual round-trip of about 30,000 kilometers between opposite ends of the globe, from Arctic breeding grounds to Antarctic seas.[9]" Another fascinating fact regarding bird migration is the ability of some birds to fly continuously for days. "The longest nonstop migration (10,300 km) is that of the Bar-tailed Godwit, which flies from Alaska to the North Island of New Zealand. …This migration, requiring at least eight days and nights of continuous flight, is a remarkable feat of navigation. The Red Knot, an arctic breeder, migrates across the equator to high southern latitudes, with nonstop stages lasting several days. Many passerines cross the Mediterranean and the Sahara Desert without stopping. [6]" Migration distance and pattern vary from one type of bird to another, yet migration in general poses an intriguing question: How do birds navigate?

     The publication "Migration of Birds"[12] states that for human beings it took many centuries to master the art of navigation. While it is somewhat simple to navigate in a small area full with landmarks, it becomes harder once the area enlarged and some landmarks change. It is even harder to navigate in areas where the scenery hardly changes for miles and miles, such as in the cases of large deserts and oceans. Human beings traveling large distances in the past have learned to rely on the "sun movement" from east to the west during the day, and on the "northern star," and stars in general, during the dark nights. With the technological advancement over the years, new ideas and inventions were developed. The compass and the GPS had replaced the old systems that relied on natural observations. Birds do not posses the ability to implement and use technological tools such as those developed by human beings, yet they do find their way year after year with remarkable accuracy. The publication "Migration of birds"[12] suggests that bird navigation has been first studied using the assumption that birds navigate purely by using visual landmarks. This perception was based on the logical analogy humankind projected from its own experience and abilities. Results of research done during the twentieth century on the subject have suggested much more sophisticated and complicated navigational techniques.

      "Navigation requires knowing three things: current location, destination, and the direction to travel to get from the current location to the destination [12]. " An experiment described in the "Migration of Birds" publication by Lincoln, Frederick C., Steven R. Peterson, and John L. Zimmerman in 1998[12] states that some birds possess "built-in" information regarding their migrating direction and distance. According to the publication, Perdeck had relocated thousands of Starlings from Holland and released them in Switzerland. "…the adults, who had previously made the migratory flight, knew they had been displaced and returned to their normal wintering range by flying a direction approximately ninety degrees to their usual southwesterly course. The juveniles, which had never made the trip before, in contrast, continued to fly southwest and were recaptured on the Iberian Peninsula. These first-year birds "knew" what direction to fly, but did not recognize they had been displaced, thus ending up in an atypical wintering range. In subsequent years, these now adult birds returned to again winter in Spain and Portugal. … Perdeck concluded that the proper direction of the migratory flight was innate, that is, inherited in their DNA, since the naive juveniles could fly that direction, and that the birds were also genetically programmed to fly a set distance. … this study demonstrated that this navigation system is modified by experience, since adults knew they were not in Holland any longer and knew that in order to get to their normal wintering grounds they needed to fly a direction that they had never flown before![12]." "In summary, a young bird on its first migration succeeds in navigating to its population specific over-wintering site without a map sense of where. A genetic program that defines which direction and how long to fly seems sufficient to get them close, and in the literature this type of navigation is often referred to as 'vector navigation.'[5]" A further more complex "preprogrammed" navigational orientation is described by Kenneth B. Able in his article "ORIENTATION AND NAVIGATION: A PERSPECTIVE ON FIFTYYEARS OF RESEARCH"[1]. "In the Pied Flycatcher (Ficedulu hypoleucu), however, the situation seems more complicated. The well-known shift in direction from SW to SE that occurs in the field was observed in the orientation cage only when the birds were subjected to a series of changing magnetic field conditions that simulated those that would be experienced during southward migration (Beck and Wiltschko, 1982). This remarkable study which has not to date been replicated, suggests a complex interaction between the endogenous temporal program controlling migration and an environmental cue: only when the appropriate magnetic field (presumably indicating latitude) is experienced at the proper time does proper orientation occur."

     In addition to the inner programmed orientation that some birds seem to possess, research done suggest some other navigational skills that some birds possess. One of them is using the sun as a navigational aid. This navigational mechanism has been named "Sun Compass" and is described by Withgott, Jay in the article "Birds Follow the Sun" [15]. The article overviews research done by Alerstam in order to demonstrate bird's usage of the sun as a navigational aid. He points that observations show that "…migrating plovers and sandpipers were curving ever more southward as they flew east. The researchers ruled out other orientation cues and discovered the birds were using a sun compass…. But the birds' internal clocks can't keep up with their nonstop movement, apparently, and they become out of phase with local time. By failing to compensate for their movement across time zones, they misread the sun's position and veer increasingly southward. But this fortuitous mistake allows the birds to fly south in trajectories approximating the great circle routes that minimize travel distance, saving them valuable energy [15]." Another issue that Alerstam pointed out in his research is the ability of birds to compensate during flight for the directional drift caused by winds [14]. The "Sun Compass" was also demonstrated in an experiment described by Verner Bingman, Tammy Jechura, & Meghan C. Kahn in the article "Behavioral and Neural Mechanisms of Homing and Migration in Birds"[5]. The experiment involved changing the birds' internal clock by using artificial light. "…for example, "the lights in the room would come on at midnight and go off at noon basically advancing the day of the birds six hours relative to the light-dark cycle of the natural environment. Birds kept in these conditions for a week or so would experience a shift in their circadian rhythms; a rhythm would recalibrate to the changed light-dark cycle such that the circadian rhythm's morning would correspond or entrain to lights coming on, which would be midnight with respect to the natural environment…." "The bird would then be tested for its orientation, either by letting it fly or in a cage, during the natural morning when the sun is in the east. …the reading of its circadian rhythm would indicate that it is noon … and … actually observe the bird orient not in the desired southerly direction but east! Why? The midday sun is in the south and according to the bird's internal rhythm, it is noon and it should fly toward the sun. But the sun is really in the east during the environmental morning; therefore movement toward the sun is actually an easterly movement and the wrong direction. This type of clock- or phase-shift experiment that has demonstrated that birds, and other animal groups including monarch butterflies (Mouritsen & Frost, 2002), use their internal sense of time to calibrate the movement of the sun in the sky. This enables them to use the sun as a stable reference to define compass directions in space. [5]"

     Another navigation method, suggested by researchers, that relates to the sun is "…skylight polarization derived from the sun. [5]" Birds "… can do so because the properties of skylight polarization change predictably with the changing position of the sun (e.g., Able, 1982). Bird visual sensitivity to ultraviolet light, like that of bees, may be important in detecting skylight polarization.[5]" This ability can help birds navigate at twilight time allowing for continuous traveling when the "Sun Compass" is fading out and the stars are not bright enough yet for "stellar navigation".

     While some birds are traveling during the days and resting at nights, others are traveling at night and during the day they "refuel" and rest. For these birds' the stars are essential in order to determine their flight direction. "Stellar navigation" it seems plays an essential navigational aid for birds migrating during the nights. Keith Devlin describes in "MAA Online"[11] that research has shown that star navigation is not based on pattern recognition but on movement recognition of the skyline around an anchor star. "At least one species of birds -- Indigo Buntings -- use the stars to navigate at night. …a few years ago, a study found that nestling Indigo Buntings in the northern hemisphere watch as the stars in the night sky wheel around Polaris -- the north star, located above Earth's north pole. ...To test this hypothesis, the researchers showed the birds a natural sky pattern inside a planetarium. They seemed to fly in a direction consistent with being able to detect the motion of the stars. They knew in their own way which direction was north. When the experimenters changed the set up so that Betelgeuse was now the pole star which the stars rotated around, the birds flew in a direction consistent with Betelgeuse being the pole star. They no longer went where they should have relative to Polaris. So, they weren't using the locations of specific star patterns. It was just that they were noticing which star the others rotated around. In other words, it wasn't the star patterns, but how they moved that counted.[11]"

     Although "Stellar navigation" and "Sun Compass" are useful methods for navigation, simple logic, research and migration observation show that birds cannot rely on one of these methods solely. Birds continue on their migration route during cloudy days and nights when it is hard to determine the sun or the celestial pattern. "In a 2007 article in the German journal Naturwissenschaften scientists announced that they'd found tiny iron oxide crystals in the skin lining of the upper beak of homing pigeons, laid out in a three-dimensional pattern in a way that the birds might be able to sense the Earth's magnetic field independent of their motion and posture, and thus identify their geographical position[12]." It has been suggested that birds can sense the magnetic power of the earth and its deviations. This is described by Kenneth B. Able in its article "ORIENTATION AND NAVIGATION: A PERSPECTIVE ON FIFTYYEARS OF RESEARCH"[1]. "In the Pied Flycatcher (Ficedulu hypoleucu), however, the situation seems more complicated. The well-known shift in direction from SW to SE that occurs in the field was observed in the orientation cage only when the birds were subjected to a series of changing magnetic field conditions that simulated those that would be experienced during southward migration (Beck and Wiltschko, 1982). This remarkable study which has not to date been replicated, suggests a complex interaction between the endogenous temporal program controlling migration and an environmental cue: only when the appropriate magnetic field (presumably indicating latitude) is experienced at the proper time does proper orientation occur. [1]" "…Merkel and Wiltschko demonstrated in a laboratory environment devoid of any other cues that European Robins would change their orientation in response to shifts in an artificial magnetic field that was as weak as the Earth's natural field[2]." Research also has shown that "Deposits of single domain magnetite have been found in a variety of higher animals that exhibit magnetic sensitivity, including fish, newts, birds, and mammals (Kirschvink et al. 1985; Brassart et al. 1999). Furthermore, innervated super paramagnetic magnetite has been found in the upper beak of the homing pigeon (Hanzlik et al. 2000; Winklhofer et al. 2001).[10]" A deep analyses of magnetic orientation is described by Michael J. Freake in the article "MAGNETIC MAPS IN ANIMALS: A THEORY COMES OF AGE?" The basic mystery behind magnetic orientation is the fact that a compass for example is able to direct us where the north is, yet it cannot "tell" the user of its current location. Some birds it seems poses a kind of a "magnetic map" that can point their location relative to a known point. According to the article, it seems as though this map is not inherent and a bird needs time and travel experience in order to accumulate enough information to be able to use it. Experiments done have shown that "… the migratory orientation of adult silvereyes (Wiltschko et al. 1994, 1998), but not that of inexperienced young birds (Munro et al. 1997a,b), as affected by pulse re-magnetization, which suggests that a magneto reception mechanism involving single-domain or interacting super paramagnetic particles of magnetite is involved in obtaining map information[2]." The navigational magnetic map suggested idea raises questionable issues outlined by Michael J. Freake in the article "MAGNETIC MAPS IN ANIMALS: A THEORY COMES OF AGE?" Among these questionable issues are magnetic changes over short distances (which is "…extremely week… [10]"); The earth geological structure which is not uniform; Climate conditions that result in electromagnetic fluctuations and solar wind magnetic outbursts.

     Another navigational method in use by some migrating birds is the topographical patterns of the earth. Landmark navigation is essential to some birds traveling on routes that contain natural obstacles such as mountains and oceans, yet not all birds are using landmarks when migrating. "Radar images of migrating birds subject to a strong crosswind were seen to drift off course, except for flocks migrating parallel to a major river. These birds used the river as a reference to shift their orientation and correct for drift in order to maintain the proper ground track. That major geographic features like Point Pelee jutting into Lake Erie or Cape May at the tip of New Jersey are meccas for bird-watchers only reflects the fact that migrating birds recognize these peninsulas during their migration [7]." "A flying bird overviews a wide area and may be able to identify conspicuous distant structures from varying positions and/or may refer to large-scale characteristics of an aerial panorama as a whole rather than to distinct individual landmarks [13]."

Swans Flight

     For migrating birds, flying from the nesting grounds to the wintering grounds and vice-versa the above methods and systems might be sufficient. Yet for some birds and for some homing pigeons in particular, taken hundreds of miles to new grounds and released, it seems that these systems are not enough. Hans G. Wallraf in the article "Beyond familiar landmarks and integrated routes: goal-oriented navigation by birds"[13] suggests a surprisingly different direction of thought for position decision and directional navigation. "What really appears to be used by birds as a source of positional information had never been considered as a possible candidate until Papi et al. (1971, 1972) detected that homing pigeons, deprived of the sense of smell, were very weak in homing or failed completely to return from distant sites. A variety of subsequent experiments have left hardly any doubt that displaced pigeons and other birds are able to deduce the approximate direction towards home from atmospheric trace gases perceived by olfaction at their current distant position [13]." Various researches done in order to prove or disprove this theory have not given a definite conclusion. Wallraf adds, "There is no doubt that homing pigeons as well as many wild-living birds have navigational capacities exceeding the range of landmark orientation and path integration. There is however, enduring doubt that these capacities are based on utilization of atmospheric chemo signals (e.g. Schmidt-Koenig and Ganzhorn 1991, Wiltschko 1996, Gould 2004). In view of the many difficulties obviously connected with the notion of olfactory navigation, such doubt is traceable. [13]."

     As with human beings, not all birds are alike. Over viewing, the various researches done are suggesting that some birds use a combination of all the above systems and some use parts, yet none relies on one system only. "The weight of evidence suggests that in short-term orientation decision-making magnetic cues take precedence over stars, that visual information at sunset overrides both of those stimuli, and that polarized skylight is the relevant cue in this dusk orientation [1]." "Very much is not known about bird migration. Also, only a few bird species have been studied, so it's risky to apply what little is known to all species. Finally, it can be assumed that migrating birds typically use more than one method. They probably use the technique that feels most accurate at the time.[3]"

Works Cited

[1] Able B. Kennet. "ORIENTATION AND NAVIGATION: A PERSPECTIVE ON FIFTY YEARS OF RESEARCH" The Condor (1997). 21 Aug. 2007

[2] Adler, T "It takes two compasses to fly right" (1996) Science News (Vol. 150) 14 Sep. 1996. 21 Aug. 2007

[3] Backyardnature. "BIRD NAVIGATION"(2007) 15 Mar. 2007. 21 Aug 2007

[4]Berthold, Peter. Control of Bird Migration London: Chapman & Hall, 1996 . [Partial online version] Control of Bird Migration . Google Books. Springer

[5] Bingman, V., Jechura, T., & Kahn, M.C. . Behavioral and neural mechanisms of homing and migration in birds. (2006) In M.F. Brown and R.G. Cook (Eds.). Animal Spatial Cognition: Comparative, Neural, and Computational Approaches(on-line). 21 Aug 2007 .

[6] " Bird Flight and Locomotion" Birds and birding in India. 21 Aug. 2007

[7] "Bird Migration" Birds and birding in India. 21 Aug. 2007

[8] Brown, M.F., & Cook, R.G. Animal Spatial Cognition: Comparative, Neural, and Computational

[9] Deinlein, Mary. "Have Wings, Will Travel: Avian Adaptations to Migration". Smithsonian Migratory Bird

[10] Freak(,) J. Michael, Muheim(,) Rachel, and Phillips(,) B. John. "Magnetic Maps in Animals: A Theory Comes of Age?" . The Quarterly Review of Biology (Vol. 81) December 2006,

[11] Keith(,) Devlin, "Those Amazing Flying Mathematicians"(1999) Oct. 1999.

[12] Lincoln, C. Frederick, Peterson R. Steven and Zimmerman L. John. . "Migration of birds" (1998). U.S. Department of the Interior, U.S. Fish and Wildlife Service, Washington, D.C. Circular 16. Jamestown, ND: Northern Prairie Wildlife Research Center Online. (Version 02APR2002). 21 Aug. 2007

[13] Wallraff (,) G. Hans. "Beyond familiar landmarks and integrated routes: goal-oriented navigation by birds".

[14] Wehner, Rudiger. "Bird Navigation – Computing Orthodromes". Science Now (EBSCO Host) 1 Dec. 2001.

[15] Withgott, Jay. "Birds Follow the Sun." Science Now (EBSCO Host) 1 Dec. 2001. 21 Aug. 2007