574

INTEGR. COMP. BIOL., 45:574–581 (2005)

Multi-modal Orientation Cues in Homing Pigeons1

CHARLES WALCOTT2

Department of Neurobiology and Behavior, Seeley G. Mudd Hall, Cornell University, Ithaca, New York 14853-2702

SYNOPSIS. How homing pigeons displaced into unfamiliar territory find their way home has been thesubject of extensive experimentation and debate. One reason for the controversy is that pigeons seem to usemultiple cues. Clock-shifting experiments show that experienced pigeons use the sun as a preferred compass;when it is not available they rely on magnetic cues. That pigeons can home successfully while wearing frostedlenses suggests that landmarks, while not an essential navigational cue, are important in the final stages.The sensory basis of the ‘‘map’’ or position finding system is probably equally or even more complicated.When conditions around the loft are suitable, pigeons may use olfactory cues to find their way or might usesome feature of the earth’s magnetic field for their navigation. The Wiltschkos (1989) showed that pigeonsraised without free access to ambient odors are not disoriented when anosmic while their siblings raisedwith free access to the prevailing wind were disoriented. Similarly, sibling pigeons from two lofts in Lincoln,Massachusetts. were well oriented or totally disoriented when released at magnetic anomalies under sunnyskies depending upon which of the two lofts they had been reared in. All of these experiments and manymore suggest that pigeons use multiple and redundant cues to find their way home. Further, there is thesuggestion that which cues they adopt may well be influenced by the characteristics of the area around thehome loft in which they were reared.

INTRODUCTION

Homing pigeons taken from their lofts and releasedas far away as 1,000 km in unfamiliar territory returnhome. Kramer (1953) proposed the idea of dividingthe homing process into two components, ‘‘map,’’ thedetermination of the direction toward home, and‘‘compass,’’ the process of flying in that direction.Wiltschko and Wiltschko (2003) have provided a su-perb review of the historical development of our un-derstanding of how birds home. Yet as they point outin their review, the cues that pigeons use to determinethe direction to the home loft (the ‘‘map’’) are stillcontroversial. Olfactory cues play some role in deter-mining the direction to home, but it seems unlikelythat they are the only important cue. Once the directionto home is determined, either the sun, the earth’s mag-netic field or both together serve as directional or com-pass cues. Near the loft itself, it seems likely that fa-miliar visual landmarks are important. Thus pigeonhoming depends on a variety of cues; the question dis-cussed in this paper is how does a pigeon choosewhich cue to use and are there interactions betweenthe different sensory modalities?

MATERIALS AND METHODS

The techniques used in this research are quitestraightforward. Homing pigeons are raised in a stan-dard racing pigeon loft and, as youngsters, allowedfree flight around the loft. At about 6–8 weeks of agethey are trained by being put in baskets and releasedfrom increasing distances away from the loft, gradu-ally reaching a distance of 100 to 200 miles. Pigeons

1 From the Symposium Neural Mechanisms of Orientation andNavigation presented at the Annual Meeting of the Society for In-tegrative and Comparative Biology, 2–6 January 2002, at Anaheim,California.

2 E-mail: cw38@cornell.edu

are then released singly to train them to fly homealone. To determine the direction each pigeon chooses,it is watched with binoculars and the direction inwhich it vanishes is recorded. Alternatively, pigeonsare equipped with a small radio beacon and followedwith radio direction finding equipment. The directionin which the radio signal disappears, typically 5 to 10km from the release point, is called the radio vanishingbearing. Pigeons with radios were also be followed byairplane on their route home. Michener and Walcott(1967) and Walcott (1977 and 1992) will provide fur-ther details. Recently, global positioning systems havebecome small and light enough to be carried by pi-geons (Steiner et al., 2000). These devices allow oneto get detailed and accurate information about a pi-geon’s homeward track without the necessity of fol-lowing it (Lipp et al., 2004).

RESULTS AND DISCUSSION

Landmarks

When Martin Michener and I began to follow hom-ing pigeons by airplane back in the early 1960s wethought that knowing the paths pigeons took from re-lease to home would give us important insights intotheir navigation. What we found was that pigeons, re-leased at the same location, generally followed some-what different routes home. (Fig. 1) We believe thatthese routes were really different even for the samepigeon because, for light colored pigeons, we couldwatch them fly just at the level of the tree tops. A fewpigeons on occasion flew much higher, but generallyflight was close to the ground. That means that thebirds couldn’t be following a consistent set of familiarlandmarks to find their way back to the loft even ontheir training flights, Michener and Walcott (1967).There was no evidence that pigeons consistently fol-lowed a prominent road from the release point, nor did

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

575MULTI-MODAL ORIENTATION IN PIGEONS

FIG. 1. Tracks of three different homing pigeons, each releasedrepeatedly from three different release sites. For each pigeon, thenumbers refer to the chronological sequence of the tracks. BlueWAL from Manchester New Hampshire and Blue YAL fromWorcester were returning to a loft in Cambridge, Massachusetts;Blue R19 was returning to a loft in Lincoln, Massachusetts. Thetotal length of the scale bar is 36 km. Notice the variation in suc-cessive tracks, especially for Blue R19 from Orange, Massachusetts(From Michener and Walcott, 1967).

FIG. 2. Tracks of pigeons released for the first time off their train-ing line. These tracks from the Worcester, Massachusetts airportshow the variability in strategies used by different pigeons whenreleased for the first time at an unfamiliar site. The pigeon that madethe track in the top left in the diagram had been trained from Orange,Massachusetts. On its homeward training trip it always passed aprominent mountain, Mt. Wachusett (MTN in the diagram). Noticehow, on its first release from Worcester, it seemed to head for themountain before flying home.

it seem likely that distant landmarks were usually im-portant. Recently, Lipp et al. (2004) have been usingGPS systems to track pigeons. They find that their pi-geons not only follow roads but also railroads. Onlyas they approach the loft do they desert the road. Thisbehavior certainly differs from that we saw in our Lin-coln, Massachusetts pigeons or those we followedaround Ithaca, New York. Clearly, at least some pi-geons make use of landmarks in their homing.

Yet the experiments of Schlichte and Schmidt-Ko-enig (1971) show that pigeons wearing frosted lenseswould still orient toward home and many could evenfind the loft. Tracking these pigeons by airplaneshowed that they made straight tracks toward the loftbut many landed within about 10 km of the loft(Schmidt-Koenig and Walcott, 1978). For these birdsvisual landmarks were not required either at the releasepoint or to fly a straight path towards the loft; it wasonly in the final stages of finding the loft itself thatthey seemed crucial.

Individuality

Taking individual pigeons that had repeatedly flownover the same course to a more distant, unfamiliar re-lease site revealed a number of different strategies.One bird flew for a few miles in the compass directionthat would have led it home from the familiar releasesite. It then stopped, perched for about 20 minutes, andwhen it resumed flight, headed directly for home. An-other pigeon that had been trained from Orange, Mas-achusetts and regularly passed a prominent hill (Mt.Wachusett) on its way home was released at Worcesterairport. Instead of flying East toward home, it headedNorth flying toward Mt. Wachusett even though thatwas not the way home. Having flown around themountain, it turned and headed for home (Fig. 2). Re-leased in other locations, this pigeon always headedfor the nearest mountain before flying home. Yet an-other pigeon always oriented very accurately towardthe loft, but as it got within about 10 km it would stop,find a person out gardening and we would get a tele-phone call to come and collect it! Another pigeon re-leased for the first time at Worcester airport started outheaded Southwest and made a huge circular diversionto the South.

I offer these stories only as evidence that differentindividual pigeons raised and trained under identicalconditions may well prefer to use or weight their ori-entation cues differently. When working with largegroups of pigeons, these individual idiosyncrasies be-come submerged in the group data. It is only by study-ing individuals that they become apparent.

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

576 CHARLES WALCOTT

FIG. 3. Pigeons wearing head coils were radio tracked from Carver,Massachusetts 74 km South of the loft under sunny skies. Two coilswere generating an earth strength magnetic field around the pigeon’shead, differing only in their polarity. NUP coils, placed around amagnetic compass, caused the north-seeking needle of the compassto point toward the bird’s head coil (top line), SUP coils (X lowerline) had the opposite polarity. The third line (O lower curve) rep-resents birds carrying both coils and batteries but with no currentflowing. Each point represents the average direction of each groupof birds during the first 15 minutes after release. The left verticalscale is the pigeon’s bearing relative to magnetic North; the rightscale is the bearing relative to home. Notice how the substantialdifference in bearings between the NUPs on the one hand and theSUPs and no current birds on the other at 4 minutes after releasegradually decreased to a small difference at 15 minutes when mostbirds vanished from radio range (From Walcott, 1977).

Compass systems

Sun compass. There is general agreement that hom-ing pigeons use the sun as a compass reference. A six-hour clock shift results in roughly a 908 error in thepigeon’s orientation. (Schmidt-Koenig, 1961, 1979[summary]; Keeton, 1974). Yet if one looks at releasesat different sites, the actual amount of shift varieswidely. At some release points, the bearings are shiftedmuch more than 908, at others much less (Keeton andWalcott, unpublished data). Whether this is the effectof a different ‘‘release site bias’’ (Keeton, 1973) at thedifferent sites or represents a difference in the effectof clock shifts on the sun compass is not clear.

Magnetic compass. Under overcast skies, Keeton(1974) showed that clock shifts have no effect on thepigeon’s orientation. This means that the pigeons couldnot, in some mysterious way see the sun through theclouds, for, if they did, their bearings would be shifted.Further, it means that whatever the basis of their‘‘map,’’ it doesn’t depend on an accurate sense of time.Yet the pigeons were still well oriented towards home.Keeton’s also showed that pigeons with small bar mag-nets glued on their backs were often disoriented andwould home more slowly than controls wearing brassbars. Keeton’s (1971,1972) original results includedonly those releases in which the birds carrying brassbars were oriented. Bruce Moore (1988) reanalyzed allKeeton’s data and included all the releases, even thosein which the brass bar controls were disoriented. Underthese conditions the difference both in orientation andhoming time between brass and magnet birds disap-pears. This does not invalidate Keeton’s essential pointthat when there is a difference between pigeons car-rying magnets and those carrying brass bars, it is themagnet birds that show either poor orientation or slow-er homing.

Under sunny skies, magnets had very little effectexcept when pigeons were suddenly released at muchlonger than their accustomed distances. Under theseconditions magnets caused poor orientation even undersun (Keeton, 1972 and Walcott, 1974, 1980a). Inter-estingly, young pigeons, released at an unfamiliar lo-cation for the first time under sunny skies, were dis-oriented by magnets (Keeton, 1972). This implies thatyoung pigeons, like older birds under overcast, are us-ing the earth’s magnetic field. Wiltschko and Wiltsch-ko (1981, 1990) have shown that young pigeons learnthe sun-compass by reference to the direction of theearth’s magnetic field. But why should they make thisshift? Magnetic information should be available all thetime, not just when the sun shines. There must be someimportant reason for pigeons to learn the complicatedrules of sun movement rather than continuing to relyon the magnetic compass. Cochran et al. (2004) haveshown that Catharus thrushes calibrate their magneticcompass on a daily basis using twilight cues, appar-ently just the reverse of what homing pigeons do.

Paired coils. Walcott and Green (1974) and Visal-berghi and Alleva (1979) used paired coils to generate

a uniform magnetic field around the pigeon’s head.Initially, the orientation of pigeons wearing coils gen-erating a small 0.1 gauss field, about 1/6th of theearth’s magnetic field, was compared to the orientationof birds with coils but with no current flowing throughthem and hence, no magnetic field. Under sunny skiesbirds wearing the coils with current had more scatteredvanishing bearings than those without. (Walcott,1977). A second series of experiments using coils gen-erating earth strength magnetic fields utilized two dif-ferent field polarities. By reversing the polarity of thebattery either of two magnetic fields could be gener-ated: either a NUP (in which a magnetic compassplaced between the two coils had its North seekingneedle pointing towards the coil on the top of the pi-geon’s head) or a SUP with the opposite polarity. Thisdifference in polarity had only a small effect undersunny skies. Pigeons released with an earth strengthmagnetic field around their heads vanish in slightlydifferent directions depending on the polarity of themagnetic field. This is a consistent and repeatable ef-fect and takes place under sunny skies (Walcott, 1977).While the difference in orientation between pigeonscarrying NUPs and SUPs was only 18 to 34 degreesat vanishing, the time course of their directional choic-es reveals much greater differences shortly after re-lease (Fig. 3). Pigeons released North and South of theloft with NUP coils vanish some 18 to 34 degrees tothe left of Sups and birds with no current. When re-leased from the West, NUPs and birds with no currentvanished 19 degrees to the right of the SUPs.

Repeating the same experiment under overcast

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

577MULTI-MODAL ORIENTATION IN PIGEONS

FIG. 4. The mean vanishing bearings of Cornell pigeons releasedat Castor Hill Fire Tower, 160 km NNE of the loft in Ithaca, NewYork, over a 19 year period are plotted year by year. The upper lineis for birds that had never been released at Castor Hill before; thelower line is for pigeons that have been released at the site before.The remarkable variability in the release site bias seems to haveseveral cycles over a period of years. Experienced birds typicallyshow less deflection than those new to site but the peak years oftheir deflection seems lag that for birds new to site. The deflectionat Castor Hill is always clockwise from the home direction (indi-cated by 08). Each point is the mean vanishing bearing of 3 to 6different pigeons.

showed that pigeons wearing NUP coils headed awayfrom home while birds with SUP coils homed nor-mally (Walcott and Green, 1974; Visalberghi and Al-leva, 1979). This finding strengthened the idea thatpigeons unable to see the sun rely on the earth’s mag-netic field as a compass. The dominance of the suncompass becomes particularly dramatic when trackinga pigeon equipped with NUP head coils and it is van-ishing in the direction away from home. If the sunsuddenly becomes visible for a moment, the pigeonturns and flies directly over the release point headingfor home.

Yet the dichotomy between sun and magnetic fieldis not a simple alternative. Wiltschko and Wiltschko(2001) report that when 6 hr clock-shifted pigeons re-leased under sun showed a deflection of less than thecustomary 908, equipped them with bar magnets re-stored their full 908 shift. They interpret this result tomean that the shifted pigeons were using both theirsun and magnetic compasses simultaneously. As Wal-cott (1977) suggested, there seems be an interactionbetween the sun and the magnetic compass systemscausing the deflection shown by the NUP and SUPpigeons under sun.

Map

Release site bias. Pigeons released at various sitesaround Ithaca, New York rarely head exactly towardshome (Windsor [1975]; see Walcott [1996] for a com-plete map). Pigeons exhibit what Keeton (1973) calleda ‘‘release site bias.’’ At Castor Hill, New York, 160km NNE of Ithaca, for example, a substantial clock-wise shift in vanishing bearings takes place under bothsun and overcast. This observation seems to eliminateany chance that the bias was a sun compass effect.Furthermore, the clockwise deflection was similar forother birds from other lofts. Remarkably, the amountof bias has varied over the years. As Figure 4 shows,the bias at Castor Hill slowly varies from year to year.For any particular year, it was generally greatest forinexperienced birds released there for the first time anddiminished with older. more experienced pigeons. Fol-lowing these birds by airplane showed that they head-ed West 25–32 km before they changed course quiteabruptly and headed South toward the loft. There werea few birds in the Cornell loft that exhibited no biaswhatever at Castor Hill and simply flew straight home.The offspring of these no-bias birds also showed nodeflection at Castor Hill. What these birds were doingthat differed from what our usual pigeons did is totallymysterious. But the fact that it could be inherited sug-gests that it has a genetic basis.

Jersey Hill: a Bermuda Triangle. Probably the mostdramatic example of a release point problem for Cor-nell pigeons is the release site at the Jersey Hill Firetower near Hornell, New York 135 km West of theloft. At this otherwise unremarkable release site, Cor-nell pigeons vanish in all directions (Fig. 5) and thevast majority never return home. Following some ofthese birds by airplane, Bruce Moore showed that they

wandered over the countryside mostly never gettingcloser to home. A few finally made it home by flyingin a hugely indirect route. Pigeons from several otherlofts, even Cornell pigeons raised in other lofts flystraight home from Jersey Hill (Fig. 6). Even pigeonsfrom Trumansburg, 18 km West of Ithaca are well ori-ented and home normally. Jersey Hill seems to poseproblems only for pigeons raised in the Cornell pigeonlofts on Turkey Hill in Ithaca, New York (Walcott andBrown, 1989)! Perhaps pigeons compare some featureremembered from the home loft with that at the releasesite. For most pigeons this works well, but for Cornellpigeons at Jersey Hill, it fails to provide useful infor-mation. Why Cornell pigeons flying incorrect pathsfrom Jersey Hill fail to correct them is puzzling sincethey fly over areas from which Cornell pigeons homenormally.

Loft location. That the location of the pigeon loftmakes an important difference in the pigeon’s orien-tation is shown by two experiments. The Wiltschkoshad a loft of pigeons in the garden at the Frankfurtzoological institute. Making these pigeons anosmichad essentially no effect on either the pigeons’ orien-tation or homing. Their siblings raised in a loft on theroof of the Institute, four stories above, when madeanosmic neither oriented nor homed. This differencecould be explained by the difference in the access towind and the odors it carries to the two lofts. The loft

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

578 CHARLES WALCOTT

FIG. 5. The vanishing bearings of 984 pigeons released at JerseyHill Fire Tower located just West of Hornell, New York, 137 km Wof Ithaca. Each dot represents the vanishing bearing of an individualpigeon released under sunny skies over a 14 year period. The dashedline indicates the direction to home; the length of the mean vectorof all the vanishing directions is 0.0065 at 160 degrees. Because ofthe huge number of releases, this direction is significantly differentfrom random (Raleigh Test) at P 5 0.04. Less than 10% of thesepigeons ever returned to the home loft (From Walcott and Brown,1989).

FIG. 6. The Jersey Hill vanishing bearings of young birds raised inthe Cornell loft in Ithaca, New York 135 km to the East of JerseyHill and those of young birds raised in the Reenstra loft 396 kmSoutheast of Jersey Hill. Both lofts contained young birds from Cor-nell stock and from New Jersey stock. Both groups received iden-tical training before release. Young birds of whatever stock raisedin New Jersey were well oriented and a total of 4 out of 23 birdsreturned home the day of release. Birds of both stocks raised atCornell were disoriented and only 1 out of 24 pigeons returned homethe same day (From Walcott and Brown, 1989).

FIG. 7. Pigeons living in the loft at Fox Ridge Farm in Lincoln,Massachusetts were released at a variety of different strength mag-netic anomalies. The consistency of the pigeon’s vanishing directionat each anomaly, as measured by the length of the mean vector, isplotted against the variability in the magnetic field over a distanceof 1 km in the home direction. Plotting the logarithm of vectorlength against the logarithm of the magnetic variability results in astraight line relationship (r 5 0.91) with greater magnetic variabilityassociated with poor orientation (From Walcott, 1980).

in the garden was sheltered from the wind. Pigeonsgrowing up in this environment may have learned torely on non-olfactory cues. Pigeons raised in the lofton the roof where there was free access to the windand the characteristic odors that it brought may havegrown up convinced of the utility of olfactory cues(Wiltschko and Wiltschko, 1989).

Magnetic anomalies. Another example of the samekind of phenomenon is the results obtained by releas-ing pigeons at magnetic anomalies (Wagner [summa-rized 1983]; Kiepenheuer [1982, 1986] and Walcott[1978]). These anomalies are local distortions in theearth’s magnetic field caused by changes in the mag-netic permeability of the underlying bed rock. Homingpigeons released at such locations, even under sunnyskies are generally disoriented until they leave the dis-torted area. They then head home normally. That thedisorientation at anomalies is really a consequence ofthe distorted magnetic field is supported by the findingthat the degree of disorientation is correlated with thestrength of the anomaly (Fig. 7). These results wereobtained with pigeons raised in our old lofts at FoxRidge Farm, in Lincoln, Massachusetts. Astonishingly,Cornell pigeons raised in Ithaca proved to be betteroriented at magnetic anomalies than at control, mag-netically normal sites!

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

579MULTI-MODAL ORIENTATION IN PIGEONS

FIG. 8. The relative vanishing bearings of pigeons raised in twolofts in Lincoln, Massachusetts separated by about 2.5 km. The FoxRidge Farm loft and the Codman Farm loft were stocked with sib-lings and both groups of birds were trained together. At most releasesites the behavior of the two groups of birds was identical. At themagnetic anomaly at Iron Mine Hill, near Woonsocket, Rhode Is-land, the Codman Farm pigeons were well oriented while the FoxRidge Farm pigeons were disoriented (From Walcott, 1992).

FIG. 9. A portion of the aeromagnetic map of Lincoln, Massachu-setts showing the position of the pigeon loft at Codman Farm (lefthand dot) and that at Fox Ridge Farm (right square). In this map,lines of equal magnetic intensity are shown but the normal, back-ground earth’s magnetic field in removed. The map shows that theloft at Fox Ridge Farm is located on a steep magnetic gradient of450 nT/km whereas the Codman Farm loft is located in a moreuniform magnetic field with a gradient of only 80 nT/km. FromWalcott (1992).

To determine whether this result was caused bysome difference between Ithaca, New York and Bos-ton, Massachusetts pigeons, we established a new loftof pigeons at Codman Farms in Lincoln, Massachu-setts our original site being no longer available. Thisloft was stocked with both Boston and Ithaca birds andwhen they were tested at magnetic anomalies bothgroups of pigeons flew straight home. Magnetic anom-alies had no effect. We then put a second loft at FoxRidge Farm a hundred meters or so from our old lofts.It and the Codman Farm loft were stocked with siblingpigeons and then the birds were trained together. Whenboth groups were tested at the anomaly at Iron MineHill, Codman Farm birds were well oriented but FoxRidge Farm pigeons vanished randomly (Fig. 8). Thiswas a particularly dramatic result because the twogroups of birds were siblings, they had been trainedtogether and the only difference between the twogroups was the separation of their lofts by about 2.5km. Why should there be any difference at all? Look-

ing at the magnetic map of Lincoln, Massachusetts(Fig. 9) showed that the Fox Ridge Farm loft was lo-cated on a steep magnetic gradient. There was a var-iation of 450 nT over a distance of 1 km. The CodmanFarm loft, on the other hand, was located in a relativemagnetic flatland with a gradient of 80 nT/km. Couldit be that pigeons growing up on the steep magnetichillside at Fox Ridge farm found that the magneticfield provided useful information whereas pigeons atCodman Farm relied on other cues (Walcott, 1992)?Releasing pigeons at a series of magnetic anomaliesdid not improve their orientation at the Iron Mineanomaly. Yet after returning from Iron Mine, pigeonsreleased there a second time were well oriented (Led-nor and Walcott, 1988).

If Fox Ridge Farm pigeons are using magnetic in-formation as part of their map, it is curious that theywere not bothered by head coils which generated con-tinuous magnetic noise (Lednor and Walcott, 1983).Nor did magnets have any effect on the disorientationof these birds released at the magnetic anomaly at IronMine (Walcott, 1980b).

That pigeons are disoriented at magnetic anomalieseven under sun suggests that the earth’s magnetic fieldmight play a role in the ‘‘map.’’ While Wallraff (1983,1996, 1999) has argued cogently against this idea, the

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

580 CHARLES WALCOTT

anomaly experiments certainly suggest some use ofmagnetic fields by at least some pigeons.

The picture that emerges from all these observationssuggests that pigeons might be opportunists. They mayhave the capacity to use a number of different orien-tation cues (See Wiltschko and Wiltschko, 1994,1995). Which ones they use might well be a conse-quence of the characteristics and environment of theirhome loft as well as individual characteristics of theparticular pigeon. If we add to that, the variation incues available from one release site to another we endup with a complex and variable set of possibilities.This makes a great deal of sense if we consider theevolutionary origin of homing pigeons. Their ances-tors nested on cliffs and foraged for seeds in the fields.They had to return home with food for the young.Modern racing pigeons have been bred for this abilityto return home since 4000 bc. Eight thousand years ofstrong selection both for pigeons that return (those thatfail, don’t breed!) and for doing it speedily might beexpected to result in a robust system of homing in-volving many different cues and the flexibility tochoose those that are most useful in any given envi-ronment. Given the importance of returning to familiarterritory to breed and winter, it isn’t surprising thatmigratory birds also appear to rely on multiple cues.

ACKNOWLEDGMENTS

I am grateful to the generations of graduate studentsand undergraduates who did much of the work de-scribed in this paper. I give especial thanks to IreneBrown for her extraordinary help and to Tony Lednorfor years of helpful discussions. This paper benefitedgreatly from the comments of two anonymous refer-ees. Funding was provided by the National ScienceFoundation, The National Institutes of Health, The Na-tional Geographic Society, The Office of Naval Re-search and the Whitehall Foundation, Cornell Univer-sity as well as many racing pigeon enthusiasts.

REFERENCES

Cochran, W. W., H. Mouritsen, and M. Wikelski. 2004. Migratingsongbirds recalibrate their magnetic compass daily from twilightcues. Science 304:405–408.

Keeton, W. T. 1971. Magnets interfere with pigeon homing. Proc.Nat. Acad. Sci. U.S.A. 68:102–106.

Keeton, W. T. 1972. Effects of magnets on pigeon homing. In S. R.Galler, K. Schmidt-Koenig, and C. J. Jacobs (eds.), Animal ori-entation and navigation, pp. 579–594. NASA SP-262 U.S.Government Printing Office, Washington, DC.

Keeton, W. T. 1973. Release-site bias as a possible guide to the‘‘map’’ component in pigeon homing. J. comp. Physiol. 86:1–16.

Keeton, W. T. 1974. The navigational and orientational basis of hom-ing in birds. In Advances in the study of behavior, Vol. 5, pp.47–132. Academic Press, NY, London.

Kiepenheuer, J. 1982. The effect of magnetic anomalies on the hom-ing behavior of pigeons. In F. Papi and H. G. Wallraff (eds.),Avian navigation, pp. 120–128. Springer, Berlin, Heidelberg.

Kiepenheuer, J. 1986. A further analysis of the orientation behaviorof pigeons released within magnetic anomalies. In G. Maret, N.Boccara, and J. Kiepenheuer (eds.), Biophysical effects of steadymagnetic fields, pp. 148–153. Springer, Berlin Heidelberg, NewYork.

Kramer, G. 1953. Wird die Sonbnenhohe bei Heimfindeorientierungverwert? J. fur Ornithologie. 94:201–219.

Lednor, A. J. and C. Walcott. 1983. Homing pigeon navigation: Theeffect of in-flight exposure to a varying magnetic field. Com.Biochem. Physiol. 76A:665–671.

Lednor, A. J. and C. Walcott. 1988. Orientation of homing pigeonsat magnetic anomalies: The effects of experience. Behav. Ecol.Sociobiol. 22:3–8.

Lipp, H. P., A. L. Vyssotski, D. P. Wolfer, S. Renaudineau, M. Sav-ini, G. Troster, and G. Dell’Omo. 2004. Pigeon homing alonghighways and exits. Current Biology 14:1239–1249.

Michener, M. and C. Walcott. 1967. Homing of single pigeons–analysis of tracks. J. exp. Biol. 47:99–131.

Moore, B. R. 1988. Magnetic fields and the orientation of homingpigeons: Experiments of the late W. T. Keeton. Proc. Natl. Acad.Sci. U.S.A. 85:4907–4909.

Schlichte, H. J. and K. Schmidt-Koenig. 1971. Zum Heimfindever-mogen der Brieftauben bei erschwerter Optischer Wahrneh-mung. Naturwissenschaften. 58:329–330.

Schmidt-Koenig, K. 1961. Die Sonne als Kompass im Heim-Orien-tierungs-System der Brieftauben. Z. Tierpsychol. 68:221–244.

Schmidt-Koenig, K. 1979. Avian orientation and navigation. Aca-demic Press, London, New York. 180 pages.

Schmidt-Koenig, K. and C. Walcott. 1978. Tracks of pigeons homingwith frosted lenses. Anim. Beh. 26:480–486.

Steiner, I., C. Burgi, S. Werffeli, G. Dell’Omo, P. Valenti, G. Troster,D. P. Wolfer, and H. P. Lipp. 2000. A GPS logger and softwarefor analysis of homing in pigeons and small ammals. Physiol.Behav. 71:589–596.

Visalberghi, E. and E. Alleva. 1979. Magnetic influences on pigeonhoming. Biol. Bull. Mar. Biol. Lab. Woods Hole 156:246–256.

Wagner, G. 1983. Natural geomagnetic anomalies and homing inpigeons. Comp. Biochem. Physiol. 76A:691–700.

Walcott, C. 1974. The homing of pigeons. Am. Sci. 62:543–552.Walcott, C. 1977. Magnetic fields and the orientation of homing

pigeons under sun. J. Exp. Bio. 70:105–123.Walcott, C. 1978. Anomalies in the earth’s magnetic field increase

the scatter of pigeon vanishing bearings. In K. Schmidt-Koenigand W. T. Keeton (eds.), Animal migration, navigation, andhoming, pp. 143–151. Springer, Berlin Heidelberg, New York.

Walcott, C. 1980a. Effects of magnetic fields on pigeon orientation.Actis XVII Congressus Internationalis Ornithologici, pp. 588–592. Berlin.

Walcott, C. 1980b. Homing-pigeon vanishing bearings at magneticanomalies are not altered by bar magnets. J. Exp. Biol. 86:349–352.

Walcott, C. 1992. Pigeons at magnetic anomalies: The effects of loftlocation. J. Exp. Biol. 170:127–141.

Walcott, C. 1996. Pigeon homing: Observations, experiments andconfusions. J. Exp. Biol. 199:21–27.

Walcott, C. and A. I. Brown. 1989. The disorientation of pigeons atJersey Hill. In The Royal Institute of Navigation RIN89, Ori-entation and navigation birds, humans and other animals. Lon-don.

Walcott, C. and R. P. Green. 1974. Orientation of homing pigeonsaltered by a change in the direction of an applied magnetic field.Science 184:180–182.

Wallraff, H. G. 1983. Relevance of atmospheric odors and geomag-netic field to pigeon navigation: What is the ‘‘map’’ basis?Comp. Biochem. Physiol. 76A:643–663.

Wallraff, H. G. 1996. Seven theses on pigeon homing deduced fromempirical findings. J. Exp. Biol. 199:105–111.

Wallraff, H. G. 1999. The magnetic map of homing pigeons: Anevergreen phantom. J. Theor. Biol. 197:265–269.

Wiltschko, R. and W. Wiltschko. 1981. The development of suncompass orientation in young homing pigeons. Behav. Ecol.Sociobiol. 9:135–141.

Wiltschko, R. and W. Wiltschko. 1989. Pigeon homing: Olfactoryorientation—a paradox. Behav. Ecol. Sociobiol. 24:163–173.

Wiltschko, R. and W. Wiltschko. 1990. Zur Entwicklung des Son-nenkompass bei jungen Brieftauben. J. Ornithol. 131:1–20.

Wiltschko, R. and W. Wiltschko. 1994. Avian orientation: Multiplesensory cues and the advantage of redundancy. In M. N. O.

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from

581MULTI-MODAL ORIENTATION IN PIGEONS

Davies and P. R. Green (eds.), Perception and motor control inbirds, pp. 95–119. Springer-Verlag, Berlin, Heidelberg.

Wiltschko, R. and W. Wiltschko. 1995. Magnetic orientation in an-imals. Springer, Berlin, Heidelberg.

Wiltschko, R. and W. Wiltschko. 2001. Compass orientation in pi-geon homing: A compromise between the sun compass and the

magnetic compass. Proc. Royal Inst. Navigation, RIN 01, Ox-ford.

Wiltschko, R. and W. Wiltschko. 2003. Avian navigation: From his-torical to modern concepts. An. Behav. 65:257–272.

Windsor, D. M. 1975. Regional expression of directional preferencesby experienced homing pigeons. Anim. Behav. 23:335–343.

by guest on March 1, 2014

http://icb.oxfordjournals.org/D

ownloaded from