With 6 text-figures Printed in Great Britain
SUN NAVIGATION IN HOMING PIGEONS—ATTEMPTS
TO SHIFT SUN COORDINATES
BY CHARLES WALCOTT AND MARTIN C. MICHENER*
Division of Biological Sciences, State University of New York at Stony Brook, Stony Brook, N.Y., 11790 U.S.A.
(Received 12 August 1970)
It has been demonstrated repeatedly that homing pigeons can return to their loft when released at a place they have never been before. Since the pioneering work of Kramer & St Paul (1950, 1952), Matthews (1951, 1953; summarized in 1968), Wallraff (1967) and Schmidt-Koenig (1965), it has become clear that pigeons use some form of bi-coordinate navigation.
Matthews (1951), Pennycuick (i960) and Tunmore (i960) proposed that pigeons use the sun as the basis of their navigation. Kramer (1953), on the other hand, believed that the sun was used only as a compass and that the bi-coordinate navigation of 'map' was based on a different set of cues. This view has also been adopted by Schmidt-Koenig (1965) and Wallraff (1967). The continuing debate about the role of the sun in orientation is evident in two recent reviews: that of Matthews (1968) and of Schmidt-Koenig (1965).
Both Schmidt-Koenig (1958, 1961) and Matthews (1955) have exposed their birds to artificial light-dark cycles such that the pigeons' internal clocks should be shifted out of phase with the real day. Matthews (1955) reports that birds given a 3 h shift orient as predicted by the sun navigation hypothesis; Schmidt-Koenig (1961) reports
that birds with a 6 h shift orient about 900 to the left or right of home as predicted by
Kramer's (1953) hypothesis of a time-compensated sun compass. But, if a pigeon were, in fact, released at a point where the sun was 6 or 12 h ahead of or behind loft time, it would have to fly a distance of at least 4000 miles to reach home. Since the usual homing tests are all made at distances of less than 500 miles (805 km), it could be reasoned (see Pennycuick, 1961) that such a large clock shift was in some way 'incon-ceivable' to a pigeon and that the bird might not utilize sun navigation under these circumstances. For this reason, we have tried giving pigeons smaller shifts and assessing their effect on the pigeons' orientation.
According to the theory of sun navigation, short time errors of less than an hour should move the apparent position of the loft in sun coordinates a few hundred miles on an east-west line. Such time errors should not seriously alter the birds' perception of compass directions based on the sun, so the effects of the shift on the navigation should be separable by this technique from the effects on the sun compass alone. We have reported (Walcott & Michener, 1967) the initial results of a study of such short time shifts, and their effects on the homeward tracks of individual pigeons. It is the
* Present address: Box 215, Lincoln, Mass. 01773.
purpose of this paper to report on the conclusion of these experiments, conducted during the summers of 1965-9 inclusive. We also wish to report the results of experiments in which the image of the sun at the loft was shifted with planar mirrors, thereby providing an apparent north-south shift of the loft position in sun coordinates. Finally we will report the results of experiments in which the birds were exposed to a series of treatments designed to disturb their recollection of local solar time at the home loft.
MATERIALS AND METHODS
The stock of pigeons used in these studies was obtained from the lofts of successful pigeon racers in the Boston area. The actual pigeons whose performance is reported in this paper were mainly raised in the loft at Lincoln, Massachusetts; a few were from the loft at Harvard University in Cambridge. Birds were trained by being released at increasing distances in one direction from the loft. There were four such 'training lines' used in these experiments; birds were released from the south, the south-west, the west and the north. In all cases the training direction is specified in the results. Details of the lofts, training and techniques used for aeroplane tracking of the pigeons are given in Michener & Walcott (1967).
As previously described (Walcott & Michener, 1967), birds to be treated with artificial light shifts were incarcerated singly or in pairs in plywood boxes measuring 2 x 2 x 3 ft (o-6 x o-6 x 0-9 m). These boxes and their tops were made light-tight by the application of sealant and paint, and were provided with input and output air ducts and a continuously operating electric fan. Water and mixed grain were available in excess at all times. Lighting was provided by two 75 W tungsten incandescent bulbs, providing a light intensity of about 1000 lx (100 ft-candles) on the bottom of the box. The bulbs were switched on automatically at almanac sunrise plus the amount of shift. The almanac times and the accuracy of the automatic clock had a maximum error of 30 s.
The shift boxes were kept in the cellar of a large barn, with little or no daily activity around them, and the electric fans provided a continuous background noise which was found to exceed virtually all other incoming noises. The boxes were equipped with two perches so arranged that when the pigeon used either perch it made a mark on the chart of an event recorder. One of these perches was attached to the side of the box, the other was placed in front of the feeder in such a way that a pigeon eating grain must, of necessity, step on this perch.
release point and they were not allowed a view of the sun or of their surroundings until the moment of release.
Another procedure, intended as a controlling treatment, was administered to some pigeons. They were put, singly, in a box, identical in basic construction to the shift boxes, which was kept in the centre of a large, open field. Instead of a plywood top, however, the box was covered only with a piece of oil cloth. This material is waterproof and forms a light-dispersing filter of about 10% transmission (density = i-o), through which it is impossible to determine the direction of incident light since the light emerges scattered in all directions. The box had the same fans, ducts, food and water and recording perches as the shift boxes. In such a box the pigeon should be exposed to the natural daily light cycle, but without an opportunity to view the sun's disk.
Sun navigation requires not only an accurate measurement of the sun's altitude and a sense of time, but also an accurate comparison of the sun's altitude at the release point with its position at the same time at the home loft. If a pigeon's observa-tions of the sun's path at the loft were predictably distorted for the period immediately prior to its release in unknown territory, the bird's choice of flight direction might also undergo predictable distortion.
Pigeons were confined, one at a time, in a wire cage in one corner of the south-facing wall of the loft (see Fig. 1). Besides being able to see around the compartment of the loft, their only view of the outside world was through a wire-covered port, 8 in (20 cm)
square. The view through the port was divided into two portions: the lower 200 of
the sky, the southerly horizon and the front yard could be seen directly through the larger bottom port; the sky between 30 and 8o° of altitude could only be seen through a pair of mirrors, M i and M2. Both were rear-surface plate-glass mirrors; M i was anchored firmly to the wall of the loft, M 2 was adjustable. Laterally, the pigeon could
look straight south and about 20-300 either side of it. Thus the sun was visible for
2-7-3-5 h during midday, including local noon, through the nearly coplanar mirrors. Adjustment of the mirrors was made as follows. Each day, during early morning, the mirrors were adjusted to be as parallel as possible, generally to within less than 1' of arc of being coplanar. This meant adjusting the pairs of screws at three of the corners of M 2 until the train of multiple reflexions of a pair of taut strings (one vertical, the other horizontal) appeared as straight lines, receding back into each mirror. (Multiple sets of reflexions add twice the error between the mirrors to the image, each time they are reflected. Thus, if more than ten reflexions are visible, it is easy to see an error of lessthan 1' of arc.) After this setting, which corrected the apparatus each day for warp and other distortions of the wooden frame, the desired shift to be given to the sun was set into the adjusting screws. For instance, to raise the position of the sun's image by 60' of arc, it was only necessary to move the top of M 2 toward the loft so as to tilt it by 30' (since moving a mirror by 30' changes both angle of incidence and angle of reflexion by 30', the total angle from incidence to reflexion is changed 30 + 30
Frequent checks of the operation were made by measuring the apparent sun altitude through the mirrors with a bubble sextant placed in the pigeons' viewing port. In all
294 C. WALCOTT AND M. C. MICHENER
cases the measured sun altitude was found to be within ± 1-5' of that calculated—an error typical of the sextant itself (equivalent to a shift of the loft position 17 miles (3-8 km) in a north-south line.) It might also be noted that, although the sunlight viewed at the port passed through two rear-surface mirrors, multiple or distorted reflexions were not evident, even when viewing the sun directly through the niters in
Fig. 1. A diagram of the mirror box. A pigeon in the wire cage in the corner of the loft could view the southern horizon through the lower viewing port. The pigeon could see the sky 30-80° above the horizon through a periscope arrangement consisting of two mirrors M 1 and M 2. M 1 was rigidly fixed to the loft. The angle of M 2 could be adjusted by means of its mounting screws. Further details are in the text.
the sextant. Thus, there were no obvious visual clues that the sun was not being viewed directly. Pigeons were confined to the mirror box for 10-14 days, and it was interesting that most birds spent much of their time in the area where the patch of sunlight was reflected on to the floor of the loft by the mirrors. When the sun was not visible the pigeons seemed to show no preference for any place in their wire enclosure.
tried to have at least orie control release of a pigeon from the same point. Fig. 2 shows all the releases treated here. The proportion of experimentals and controls at each point is clear from the symbols.
B H No treatment
| | | Cloth box
| | 'Zero' shift I 5, 10,15,20,
Fig. 2. A map of all the release points used in this study. At each point the 10 mile vanishing point for each pigeon is indicated by a bar at the perimeter of a circle 5 miles in radius centred on the release point. This represents half the correct distance, thus the true position of the pigeon at 10 miles was twice as far from the release point as indicated on the map. The thin line at each point is directed at the loft. Each bar is coded to indicate the treatment that the pigeon had received before release, and the markings used are the same as those given in Fig. 4.
of change of altitude. It is clear that an accurate measurement of the rate of change of altitude will require more time than just the instantaneous measurement of the altitude. Regardless of how or in what form these sun coordinates are perceived by the bird, the information each contains will finally contribute to the estimation of the goal position in two orthogonal directions: the altitude (H) describes the component of the goal displacement measured toward or away from the sun, azimuth, i.e. up-sun or down-sun; the rate of change of the altitude (R) describes the component of dis-placement across the sun's azimuth, i.e. left or right of the up-sun direction. Penny-cuick's analysis showed simply how the errors in either measurement would contribute to errors in the bird's estimation of the direction to fly toward the goal. For displace-ments on the earth's surface of a few hundred miles (less than a few degrees on the sphere of the earth) it may be assumed, with little error in calculation, that the com-ponents of displacement (up-sun and across-sun) lie on a plane surface. They can, thereby, be combined by orthogonal vector addition, rather than requiring the solution to a three-dimensional problem. It is also expedient to consider the bird's displacement from its goal as being the vector sum of two 'errors' in the measurement of H and R. Thus, a bird displaced 60 nautical miles (69 statute miles, 111 km) to the south would see the sun at noon at the same time as at the loft, but the sun would appear 60' (1°) higher in the sky. Since H would be found to be too large, the bird should fly away from the sun, effectively lowering the sun in the sky by following the curvature of the earth away from the sun and approaching its loft. This relationship can be written as an error in the H direction, producing a component of 69 miles in the down-sun direction. The rate of change, R, at that time would be the same for both loft and release point, i.e. zero at noon, yielding a cross-sun component of zero. More completely
AH = Hiel-Hbome and SH = (69-09) (A/f) in statute miles. (1)
Ai? = i?rel -Rhome and SB = (2g6i)(Q)(AR) also in statute miles, (2)
where SH and SB are the sunward and cross-sunward components, respectively, of
the actual displacement in miles; Q is defined by Pennycuick as I cosH
where D is the declination of the sun; H and R refer to the altitude and its rate of change at the release point. In practice, as Pennycuick shows, Q varies with season and time of day, between o and about 2-0.
When released in unfamiliar territory a pigeon might first compute these two com-ponents, and then the resultant direction to the loft. Of course, no claim is intended that the pigeon manipulates symbols in the way the term ' compute' is normally used; all that the theory implies is that the behavioural equivalent of computation of the home direction would have to be based on the informative elements of the sun's position which we conveniently represent by H and R.
the entire track of the bird is shown. At the time of release the sun appeared at an
altitude of 51*20° (Hiel); its rate of rise was RTel = —o-38o°/degree of rotation
of the earth (i.e. the sun was descending, early afternoon); the azimuth (Z) was 210-8° (approximately SW.). The sun-navigation hypothesis postulates that the pigeon
com-pares Hiel and i?rel with the remembered-projected values at the loft at that time:
HL = 50-71°; RL = - 0-377. Thus the sun is higher at release by AH = +0-49° and
the pigeon should fly away from the sun (i.e. NE.) for SB = 33-8 miles (54-5 km).
The rate of increase in altitude is too negative at the release point by Ai? = 0-0034°/ degree of rotation, as compared with that at the loft, so the pigeon must fly right of
the up-sun direction (i.e. NW.) for SR = 9-3 miles (14-9 km). As Fig. 3 shows, the
vector addition, assuming the earth's surface to be a plane, produces a resultant 35*1 miles long (54-5 km), directed at the loft.
Fig. 3. The track of pigeon 1534 superimposed on a diagram of sun coordinates. The pigeon had been exposed to a 5 min clock shift before release. The dotted line indicates the pigeon's track which first crossed the 10 mile circle from the release point to the south-east. This gave a smaller training compass error than home error. From the map and diagram, it can be seen that there was little or no suggestion that the pigeon was following either of the vectors derived from sun coordinates or was orienting towards the false home.
this false home the sun's course is identical with that seen at the loft, but each point on the course occurs T minutes before or after that point as seen at the loft.
In the present case, shown in Fig. 3, the pigeon actually had been given a 5 min shift: the lights in its box went on exactly 5 min after sunrise, and off 5 min after sunset. This corresponds to a point exactly 5 min (1^° or, at this latitude, 63-8 miles, 102-6 km) west of the loft on the same line of latitude. The false home is also shown on Fig. 3, along with the sun-navigation components. £±H is very small, since the sun's altitude at release is nearly the same as that at the false home point, amounting to
SH = 2-o miles (3-2 km) displacement down-sun; R is large (—o-O239°/degree),
giving a right of up-sun component of SB = 64-6 miles (103-9 km).
However, as the track shows, the bird gave little evidence of flying towards the false home; it began flying SSE., in nearly its compass direction, then flew back past the release point and thence, semi-directly, to its loft. At no point in the track did it appear to orient toward the false home. This result is typical of all our releases; no clock-shifted pigeon ever flew to or investigated the false home area. Most were quite well oriented to the home loft when released in unfamiliar territory. Fig. 2 shows, as a composite map, the directions of the 10 mile bearings for all the tracks reported here. The 10 mile bearing is simply the bearing of that point at which a pigeon was 10 miles from the release point. At each release point, each 10 mile bearing is shown as a rectangle on the periphery of a circle. The rectangles contain symbols showing the sort of treatment given each bird, and are lumped to the nearest io° category. Owing to a lack of space between adjacent release points, the illustration shows the bearing points at a scale radius of about 4 miles, but the miles scale at the right can be used to indicate accurately the points 10 miles from the release points. For each release point a fine line indicates the direction to the loft (L). The release points were new to the pigeons in every case, so that the pigeons could not have been orienting by land-mark recognition. The map shows that, regardless of treatment, most of the pigeons started off in the homeward half of the circle for all release points around the loft.
Table 1. A summary of the results of the different treatments on homing performance (The means are followed by standard deviations; the terms are denned in the legend for the Appendix table. Home/compass ratio is the number of birds that had smaller home errors/to smaller compass errors. In three cases the home error was equal to the compass error; such cases are indicated by ?.)
Treatment No treatment Cloth box 0 shift 5 min shift 10 min shift 15-20 min shift 120 min shift 6 h shift Mirror box
Number of tracks
35 7 8 5 6 4
Homing speed 12-6 + 95 11-5+ 10-5 10-3 ± io-6 6-o±6-9 iS-8±n-3 I 6 - I ± 8-8 123+ 6-3 5-5 ± 6-6
Length ratio 1-785 + 1-14 i-8o9±i-i3 1-860 + 0-638 1-420 ±0237 1-790 + 0-933 i-756±o-577
1-506 + 0-550
i5-7± 6-o 2 i - 6 ± n - 6 19-8 + 9-9 2i-9±i4-4
7 0 + i-8 11-4+ 9-8 Only two of five birds returned
1-454 + 0-280 n - 9 ± 3-5
Home/ compass ratio
23:9 5 = 2 7 : 1 3 : 1 : ? 2 : 4 3 : 0 1 ? 7 : 2 1 ?
8 : 2
between controls and experimentals. Rather than publish all the tracks here, we have given the results of various measurements made on them in Appendix table, p. 313. Table 1 is a comparison of these measurements for all the different experimental treatments and for the controls.
To analyse the 10 mile bearings with respect to treatment, we subtracted each of several reference directions from each bearing and recorded the difference. For each 10 mile track bearing (see Fig. 3), the angle between it and the direction to the home loft is called the 'Home Error'; the difference between the 10 mile track bearing and the previous training direction is the ' Compass Error'; and the difference from the predicted false-home direction is the 'False Home Error'. Fig. 4 shows the same 10 mile bearings as in Fig. 2 but compiled with respect to the different treatments and with the 'errors' with respect to the three reference directions. The first column indicates, for that group of releases, the direction to home plotted as compass directions from the release point. This is included to show that we did not release the birds randomly around the loft for all treatments and thereby introduce a directional bias in some of the expected flight directions. The second column shows the 10 mile bearings, and, like the first, north (or o° of azimuth) is at the top of the diagram, as on a map. The next three columns to the right are distributions of 'errors', with zero error now at the top of the page. Thus, a 10 mile bearing directed in exactly the trained compass direction would be shown in column two as a rectangle pointing in that training direction (e.g. SE., 135° clockwise from north); in column three, it would show as a zero compass error, at the top of the diagram; in columns four and five it would appear at random with respect to the loft and the false home (each, o° of error at the top of the page), depending on the exact choice of release point and shift. For each diagram the Rayleigh test was employed (Batschelet, 1965) and an empirical formula (see note) was used to estimate P, the probability that the observed samples were drawn from a randomly scattered parent population. The estimate of P is shown inside each diagram. Also, for all diagrams with a P of less than o-i, the mean vector direction is shown as a heavy line projecting out of the circle.
Since for every treatment the same data are presented in each of several ways, it may help avoid confusion if we review the properties of a nearly perfect and conclusive experiment, in terms of the various diagrams. Ideally, the choice of release points should be such that the home directions for different birds released after a treatment should appear random (P large, nearly 1 -o). In addition, if there is no tendency for the birds to fly in a fixed direction, the 10 mile bearings should also appear random with respect to north as a reference. Then if the data show consistent orientation to only one reference direction, e.g. the home loft, the scatter of errors in this category should be reduced, with the points grouped tightly at the top of the circle and P very small. The other two 'error' diagrams should show the same wide scatter as the first two diagrams.
larger than o-2. Only the home errors show significant reduction in P, being approxi-mately equal to o-ooooi, shown to the nearest three digits. Not only is the scatter low, but the mean direction is oo6°, i.e. 6° right of home. Thus, the untreated birds were well oriented to the loft within i o miles of being released, and showed neither a tendency
Home directions from release
points Releases from new points, 4
off training line with V m
No treatment " 1 0-200 ZT
Ten-mile track bearings
•f 0-407 f
Ten-mile training com pass
J 0-903 •
Ten-mile home error
d 0-000 ]
5 min shift
15-20 min shift ( 0-192
120 min. shift
Six-hour shift ( 0-475
Mirror box- I 0003
to fly in a fixed compass direction nor a tendency to orient in their trained compass direction as had pigeons studied previously (Michener & Walcott, 1967).
In a similar way it is possible to analyse the two treatments originally regarded as controls. These were designed to assess the effect of the 1-2 week incarceration in a shift box. The 'cloth box' results are unclear. Only seven releases have been made and neither compass error nor home error show a scatter reduction that is significant,
although six of the seven home errors are less than 900, whereas only three of the
compass errors are less than 900. That is, the 10 mile bearings were closer to being
homeward orientated than to the direction of previous training.
The 'zero' shift refers to pigeons put in a clock-shift box in which the on and off times of the lights exactly matched almanac sunrise and sunset for the loft. There were only four birds which actually were released after this treatment, and the choice of release points was restricted to north and NW. of the loft. Thus, the 10 mile bearings show a significant tendency to head SE., yet there is no reason to believe that this treatment would favour a fixed direction tendency over the pigeons' already estab-lished tendency to head homeward. But here again the home errors are not significantly
clumped; they are all less than 900, and more closely grouped than the compass errors.
It can be said, then, that these two sets of data, small though they be in number, show that birds held in boxes for 8-14 days do orient to the loft almost as well as they do after merely having been released with no treatment other than the displacement.
Clock shifts of 5-120 min can be considered together on the basis of the scatter diagrams, as an examination of their home errors will indicate. Several points stand out: (1) the majority of 10 mile bearings were within 90° of the home direction, with the scatter of home errors, measured as a probability of randomness, all less than 0-06. (2) The mean directions of the home errors progress from 11 ° left of home (349°) with 5 min shifts, to 37° right of home with 2 h shifts. (3) In no case do the false home errors show a reduction in scatter over the raw data (10 mile bearings with respect to north) nor are they grouped in the false-home half of the circle. (4) The home errors are, in three of the four categories, less scattered than the compass errors, the exception being the bearings of birds given a 10 min shift. These points will be more fully discussed below.
The 6 h shifts, five in number, seem random with respect to all possible explanatory directions: neither compass, nor home, nor false-home errors show any scatter reduction.
The birds released after being given mirror-box shift were well oriented toward home. The calculation of the false-home direction for such shifts is as straightforward as that for the time-shifted birds. A pigeon watching the sun through the mirrors, which shift the noon position (and, proportionally, the rest of the sun's path as well) to an altitude 31' higher than normal at the loft, should home to a point on the earth's surface where noon occurs at the same time as at the loft (on the same north-south line) but where the sun appears 31' higher than that at the loft. This is exactly equivalent to tilting the horizon by 31', or to moving to a point 31' of latitude to the south of the loft (31' of latitude = 31 nautical miles = 36 statute miles = 57 km). The following shifts were given: five of 31' (three higher, two lower altitude); five of 70' (two higher, three lower); and one with no net shift up or down. As the last row of Fig. 4 shows, neither compass errors nor false-home errors were significantly clumped, while the
home errors showed very little scatter (P = 0-002) and a mean of 3320 or 280 left
The homing speeds and accuracy of the straight track segments shown in Appendix table (portions of tracks in unfamiliar territory which are at least 20 miles long yet deviate from a straight line by less than + 1 mile along their entire length) of all the groups were comparable to those published previously (Michener & Walcott, 1967) except for the 6 h shifted birds; only two of the five ever homed, and they averaged i-o5miles/h, as compared to 6-86miles/h for the 'zero' shifted birds. The poor returns made us reluctant to increase the number of 6 h shifts in our sample.
Discussions of shifts
The results reported here do not agree with the tentative summary we gave in our previous paper (Walcott & Michener, 1967). The numbers of tracks and experiments were, at that time, quite small, and evidently the sample was not representative. Taken as a whole, the results reported here, like those of the longer shifting experiments of Schmidt-Koenig (1961), argue strongly against the sun-navigation hypothesis. There is no evidence that shifts of 5-120 min were disorienting to pigeons released in unknown territory. The only treatment that affected homing speeds was the 6 h shift treatment It could be argued that, with so large a shift in the sun compass, the birds' courses did not converge on the loft; and it is well known from the work of Schmidt-Koenig (1961), Keeton (1969) and others that birds with 6 h shifts home poorly.
being active each day than under the conditions of the normal loft. The sun-navigation hypothesis would suggest that a pigeon confined under conditions of shorter days during the north temperate summer time would conclude it was at a point well south of the loft (if the bird held the season to be a constant), or that the incarceration at the loft was further south (in sun coordinates) than normal, and refer the sun coordinates of the release point to that southerly location of the projected loft (if the bird held the place of incarceration to be constant). In the first case the pigeon might fly nearly due north from any release point within 100 miles of the true loft; in the second case the bird would orient in a predominantly southerly direction, calculated to bring it back to an area to the south of the real loft, where the summer days are shorter and the nights are longer. These two interpretations are mutually exclusive, but, as can be seen from Fig. 4, second row, second column, the 10 mile track bearings were neither all northerly nor all southerly. Here again, the results are in conflict with the various possible interpretations of the sun-navigation hypothesis. We think it probable that the effect on the initial orientation may be the spurious effect of so small a sample,
especially since six of the seven home errors lie at less than 900 from zero, indicating
a homeward tendency, even if rather scattered.
There is a suggestion from the data that the clock shifts only affected the initial orientation via predictable disruption of the sun compass. If one looks (Fig. 4) from the 'zero' shift down the home error column to the 120 min shift, there is a noticeable progression from the left of the home direction to the right, as predicted from the direction of the shift. For the shifts of less than 20 min this compass shift would not be noticeable in the data, with the orientation diagrams as scattered as they are, since the change in the sun's azimuth during 20 min varies with the time of day, but usually
amounts to approximately 5—120 clockwise. In order to analyse this problem accurately
the sun azimuth was calculated for all shifts for each release point and time. This was subtracted from a similar calculation made for the sun at the loft at the effective shifted time. This difference (AZ) gives the actual azimuthal shift expected for each 10 mile bearing, since it compares the birds' best estimate of the sun azimuth at the true loft at the exact shifted time, with the actual sun azimuth as seen at the release point. The 10 mile bearing errors for the 120 min and 6 h shifts are shown in Fig. 5, corrected in each case for this shift in sun azimuth (AZ). If the shifts affected only the sun-azimuth compass, such a correction applied to each home error datum should both narrow the scatter of the home errors and pull the mean vector closer to the true home direction. As Fig. 5 shows, the results of these individual corrections produce exactly this effect for the 2 h shifts (compare with Fig. 4, 120 min shift row). The compass errors and false-home errors still appear largely random, but the home errors are less scattered (P = 0-004 instead of 0-012) and directed more nearly toward home (mean direction
50 left instead of 370 right). The 6 h shifts still, after the subtraction of AZ from the
initial bearings, appear random in every respect. Here again, the 6 h shifts appear to be disruptive in their effects on our birds.
regard the experience as evidence of its having been transported several miles in a westerly direction. During its stay in the shift box the bird might remember this apparent transportation, and, if and when it was able to escape from the box, it should fly east. The predicted false home, then, might well be to the east of the release point, rather than the west.
120 min shift
Ten-mile training compass .error
Ten-mile home error
Ten-mile false home
6 h shift 0 628
Fig. 5. The 10 mile bearings of birds with 2 and 6 h shifts corrected for actual change of sun azimuth. Only the birds with 120 min shifts showed a decrease in their home errors, from 37° to the right of the loft in the uncorrected figure to 5° to the left when the change in apparent sun azimuth caused by the shift was taken into account. The results from the few birds given 6 h shifts were too scattered to reveal any difference.
The whole issue hinges upon the pigeon's believing that the shift box is a place close to the loft. This consideration would lead to an entirely different set of false homes than are shown in Fig. 4. We have repeated the analysis with our short-time shifts considering this point, and we find that the orientation toward the home loft still shows the best orientation; there is no statistical difference between the errors to the two false homes.
The mirror-box results seem less subject to the ambiguity of the two false homes since the pigeons were, in this case, confined in one corner of the actual loft, in full sight and hearing of the other birds. Nevertheless, we have also checked each mirror-box result, and reversing the direction of the false home leads, if anything, to more widely scattered false-home errors.
It may also be possible that, as Pennycuick (i960) points out, pigeons may selectively
use one set of sun coordinates at a time (e.g. RH, SH) because they are easier to evaluate
more accurately at a particular time of day than the others (SR). Thus some birds
any part of the information in any consistent way. There was no correlation of any aspect of the sun's coordinates with any aspect of any pigeon's track.
Matthews (1955) has suggested that pigeons' chronometers might be unaffected by regular light-dark regimes, while their activity rhythms and sun-compass clocks might show entrainment. Our time-shifting results, even though involving longer periods of exposure to the shifted regime than normally employed (8—14 days instead of, e.g., Schmidt-Koenig, 1961, 4—7 days) are still open to this criticism. A similar argument might be found against the results with the mirrors—perhaps birds as old as the ones we used (1-3 years) had already worked out the sun's course at the loft so well that the mirrors were simply not believed. In an attempt to clarify these remaining diffi-culties, we performed one more shifting experiment which combined several treatments at the same time.
If a pigeon is navigating by using the sun, it must have a memory of the solar co-ordinates at a given time of day at the home loft. In the shift experiments reported above, the pigeon was isolated in an enclosed box (for as long as 14 days) under artificial lights, without an opportunity to see the sun. Yet, such birds homed as well as controls. It has been commonly reported in the pigeon-racing literature, that birds displaced from the home loft and held for substantial periods of time, even up to a year or more, home rapidly to the original loft when released. That such birds could have a clock accurately entrained to solar time at the home loft seems unlikely. Yet, it would be helpful in evaluating the theory of sun navigation if one could unequivocally destroy a bird's recollection of time at the home loft and then assay its ability to navigate. While there is no way of being certain that the bird's clock is completely uncoupled from time at the home loft, there are techniques that should make such coupling less probable. We have used two techniques: random light-dark intervals
and giving pigeons 30% D2O in their drinking water.
Matthews (1953) has shown that the chronometers of pigeons could be thoroughly upset by treating them for 4 or 5 days with very irregular light-dark cycles. In addition
Suter & Rawson (1968) have shown that D2O slows down the circadian activity rhythm
in the deer mouse (Peromyscus) and L. R. G. Snyder (in preparation) has shown the same effect in homing pigeons. Snyder reports that pigeons, in constant dim light
and given 30 % D2O in their drinking water, slow their free-running activity rhythms
by 3-5 %. This amounts to a change of 45-75 min/day. The full effect appears within
5-7 days after the pigeons have begun drinking the D2O.
Birds, whose previous homing performance was well known, were exposed to
irregular light-dark cycles while being given 30 % D2O in their drinking water. The
homing performance of such birds was compared with that of birds taken directly from the loft. Mere time disruption, however, would affect both sun compass and sun navigation leading to a scattered pattern of initial orientation. It was somehow neces-sary to allow the pigeons to re-synchronize their clocks to a time reference sufficiently close to loft time that the sun compass would not show any appreciable error, but with enough time difference so that sun navigation would be predictably upset.
3 August 1969, six were put into two shift boxes with a random light schedule identical
to that used by Matthews (1953) to disrupt their chronometers. Food and 30% D2O
drinking water were available at all times. The treatment was maintained for 9 days. The remaining three were left in the loft.
On 12 August the six pigeons were put into a covered cage and flown to Ithaca, New York, where they were held for us by Dr William T. Keeton and Mr Andre Gobert in an outdoor flight cage. This allowed them full view of the terrain, sky and sun for an additional 6-9 days. Food and normal drinking water were available for this time. Each- bird was then provided with a transmitter, placed again in a covered cage and flown east to Orange, Massachusetts, and together with the three taken on that date directly from the home loft were released and individually tracked by ground stations and aeroplane. This release point is 52 miles (84 km) west of the loft and 213 miles (343 km) east of the Ithaca holding cage. In a north-south direction, the holding point at Ithaca lies 2-8 miles (4-5 km) north of the line of latitude of the home loft, and the release point at Orange Airport lies n-o miles (17-7 km) north of this same line. In terms of sun navigation, the progress of the sun at the holding point and release point appears identical to that at the home loft within 10' of arc (about one-third the diameter of the sun's disk) except that they occur at different times of day. The differ-ence in local time, therefore, is the only reliable basis by which an observer using celestial navigation could tell apart these three points. Pigeons transported to Ithaca
after 9 days of disrupting lights and D2O treatment should, at the very least, have no
accurate evaluation of the time difference between the loft and the holding point (amounting to about a 20 min time shift).
No treatment D2O, disrupting lights,
holding 260 miles west of the loft
Loft 104° \ 7 5 ^ Loft 104° 113°, mean vector Y\
133°, mean vector
Fig. 6. The results of the disruption experiment. Birds taken from the loft with no treatment showed an average orientation 290 to the right of the direction to the loft; birds which had been
treated with DaO, random light schedules and being held 260 miles west of the loft showed
an average orientation of only 9° to the right of the loft. Both groups were well oriented at 10 miles from release with very little scatter
An exact prediction of the pigeons' behaviour after this treatment is impossible to make because so many variables have been introduced. We can imagine three possi-bilities: (1) the birds might fly west and return to the Ithaca loft. This might be the outcome if the navigational clock had been entrained to Ithaca time. (2) The pigeons might fly randomly in any direction. This might be the result for a number of reasons,
including some specific effect of D2O, or the effect of irregular photoperiod. This
seemed the most likely result since so many factors might combine to produce it. (3) The pigeons might simply return to the home loft indicating that their navigation had been unaffected by our treatments.
birds exposed to the disruption and holding, as well as the bearings of the three birds with similar training taken directly from the loft to Orange Airport and tracked on the same days as the experimentals. To these three tracks were added three 'no treatment' track bearings from Orange taken from the first part of this paper (see Fig. 2, release point' ORG', the three black rectangles), bringing the number of birds in each group to six. All 12 were unfamiliar with Orange Airport. It is clear that the initial orientation of the treated birds was, if anything, slightly better than that of the controls: P = 0-004
as opposed to P = 0-008 for the controls, mean vector 90 right of home as opposed to
29° right of home for the controls. Since complete tracks were made of the six treated birds and of four of the control birds, a further analysis was made. The two groups differed in only one noticeable respect: the treated birds tended to perch longer and fly less than the controls, and thus averaged 10-9 m.p.h. homing speed as compared to 22-8 m.p.h. for the controls. This might well be expected for pigeons carrying transmitters which had not flown freely for 15-18 days. It also might have been due
to a weakening effect from the dosage of D2O, but this point was not investigated
further. It should be said, however, that all the birds treated with D2O are still alive
and well in our loft at the time of writing.
The fact that both the control and experimental pigeons homed equally well from Orange is surprising. It suggests that either (1) the disruptive treatment was without effect upon their navigational clock or that (2) if the clock had been upset it was in some way reset at Ithaca to loft time or that (3) the pigeon's navigation does not depend upon an accurate sense of time.
It is possible, but unlikely, that neither the D2O nor the irregular light-dark cycles
had an effect upon the pigeon's navigational clock. It has been shown by Miselis & Walcott (1970) that the activity rhythms of pigeons behave like the activity rhythms that have been described for a variety of other animals. Both the onset and cessation of activity seem to be keyed to the absolute light intensity rather than to either sunrise or sunset, leading to a system whose accuracy is probably closer to + £ h than it is to + 1 min. Such an accuracy is perfectly appropriate for a sun compass but would lead to disastrous errors in a sun-navigation system. The hypothesis tested here is whether there might be another clock which was much more accurate and was rigidly fixed to solar time at the home loft. This suggestion was made by Hoffman (1965), but he cautioned that there was no direct evidence for the existence of such a stable,
loft-time clock. If such a stable clock did exist, it might also be affected by the D2O
since D2O has such a profound effect upon a wide variety of biochemical reactions
(see Thompson, 1963). Whether the effects of D2O are due to a slowing down of the
basic clock mechanism or to a delay in the expression of the clock is not clear from the literature, but it is important to note the widespread nature of its effects. It seems
to us unlikely that any biological time-keeping mechanism would be unaffected by D2O,
especially one required to maintain an accuracy of 1 or 2 min over a period of 2-3 weeks. Assuming that the navigational clock was upset by our treatment, is there any chance that the pigeon could have reset it while being held at Ithaca ? It is quite clear that the pigeons could and presumably did reset their compass clocks to Ithaca time.
But, if they had reset their navigational clock to local Ithaca time, they should have flown west from Orange rather than east. The only remaining possibility is for them to have set their navigational clock to some sort of universal Zeitgeber. But, as Snyder (1970) has pointed out, even a pigeon with access to a universal time cue will have trouble using a clock set in this way for sun navigation, because the information necessary to navigate by the sun must be referred to the constantly changing solar day at the home loft. Taking all of these factors into account then, it seems unlikely that the demonstrable system of bi-coordinate navigation used by our pigeons depends upon an accurate knowledge of time at the home loft. This conclusion is supported, in part, by Keeton's (1969) demonstration of accurate initial orientation in pigeons after 6 h clock shifts as long as the sky was overcast and the sun not visible.
Snyder (1970) has also used D2O in a pigeon-navigation experiment. He argued
that a pigeon, held in a loft, given D2O for several days, then released at a new release
point, should be, at best, unable to accurately measure the sun's rate of change of altitude at the release point. If the bird then compared this erroneous value of R with that remembered at the loft, it would orient in the wrong direction. The experi-ment was made at a place and time when the sun's altitude alone held little or no information about the direction to the loft (loft and release point lay on approximately the same Sumner circle of position). Snyder showed that the pigeons watered with
30% D2O homed as well as the controls from the unfamiliar territory. Here again,
the exact nature of the predicted errors could take a variety of different forms, depending
on how, exactly, the D2O affected the presumed chronometer; but, once again, the D2O
seemed to have no effect on the pigeons' navigation.
Since the early nineteen-fifties it has been clear that many pigeons return to their lofts from unfamiliar territory too quickly to be explained completely by their having used landmarks to pilot home. Matthews (1953) and Kramer & St Paul (1952) at first, then WallrafF (1959) and Schmidt-Koenig (1963) showed conclusively that pigeons oriented to the loft itself, as a goal, without reference to a fixed compass direction, previous training, or known landmarks. Michener & Walcott (1967) showed that individual pigeons could orient toward the loft under sunny conditions with a high degree of accuracy, again apparently without reference to known landmarks, from distances of up to 100 miles. In this study no pigeon was ever observed to fly in unfamiliar territory for more than a few miles when the sun was not visible as a disk in the sky, even though other authors have reported homing under total overcast from unfamiliar territory (e.g., most recently, Keeton, 1969).
the release point can, unknown to the observer, have breaks large enough for pigeons to get a sight of the sun somewhere along the homeward track. Instead, the sun navigation theory has been extensively considered and argued because it seemed not only the most plausible theory, but one that was predictive enough to test.
The only direct evidence for the use of the sun as a navigational reference comes from two reports by Matthews (1953, 1955)- He performed two sorts of experiments: 3 h clock shifts and preventing the birds from seeing the sun during the autumnal equinox. These experiments have been extensively repeated and discussed by several authors (Rawson & Rawson, 1955; Kramer, 1955, 1957; Hoffman, 1958; Schmidt-Koenig, 1961) who obtained results which conflict with those of Matthews. The clock-shifting results of Schmidt-Koenig (1961) and those reported here do not seem to have affected the birds' navigation. Their effect can be explained solely in terms of a sun compass. The experiments depriving the pigeon of a view of the sun during the equinox have not been successfully repeated.
The most conclusive evidence that some pigeons do not need the sun to exhibit apparent goal-directed orientation in unknown territory comes from the recent report of Keeton (1969), where pigeons oriented initially very quickly and relatively accurately under heavy overcast. Keeton also reports that pigeons with 6 h clock shifts oriented homeward more accurately under overcast than under sunny con-ditions. The use of pigeons with 6 h clock shifts effectively disposes of the possibility that his pigeons were in some way able to view the sun's disk through the clouds. These data all suggest that Keeton's pigeons have some alternative compass to use in place of the sun compass, and that it is unaffected by time errors introduced by the clock shifts. It also suggests, at the very least, that the bi-coordinate navigation, which must precede the compass orientation in new territory, is not only time independent, but also sun independent. These data, of course, show that Keeton's pigeons could and did use something other than the sun for navigation, when the sun was not visible.
The clock-shifting results, including those presented here, as well as the D2O
dis-ruption experiments show that pigeons apparently did not use the sun for navigational purposes when it was visible to them, except as azimuthal compass reference. To show that pigeons cannot use the sun as a bi-coordinate reference is clearly impossible, but the evidence against the sun's providing a coordinate system now heavily outweighs that adduced for the system. Kramer (1953) showed quite rapid homeward orientation
(apparently) by pigeons when SH was nearly zero, and the choice of homeward direction
based on sun coordinates could only be made by an accurate evaluation of SR, which
All points considered, sun navigation probably does not account for any of the observed goal orientation frequently reported in homing pigeons. What guidance system, then, could provide navigational information to these artificially transported birds, to allow them to orient routinely within ±45° of the loft direction ? This question is made the more difficult because other theories based on inertial summation by the birds or geophysical measurements have been widely discounted (see Schmidt-Koenig, 1965; Matthews, 1968). Whatever is found to provide the 'map sense' for pigeons must, apparently, have the following qualifications, as a partial list: (1) it must not depend on a view of any celestial body; (2) it must not depend on an accurate time reference to local loft time; (3) it must be independent of local or distant land-marks (since it works over the open ocean, see Fig. 2); (4) it must be operative and accurate after a period of many days of imprisonment away from the home loft, either in a darkened box or a widely removed flight cage (as in our disruption experiment). We know of no theory, yet proposed, based on known sensory processes which fully meets these qualifications.
In order to speed the calculation of P (the probability that the observed sample population was drawn from a random parent population of unit vectors) tabulated values of P (Batschelet, 1965) were used empirically to derive a computation equation of reasonable accuracy. For convenience the equation was formulated in terms of n, the number of vectors in the sample, and z, the square of the resultant vector divided by n(z = R^jn):
This equation was used throughout to estimate P. It produces a minimum error in the estimation at P = 0-05 and P = o-oi for n = 10 and for n = 00. The error at these two values of P never exceeds + o-ooi from n = 7 to 00, so the values of P shown in this report can be considered to match the tabulated values to within a few per cent of the values, if P lies between o-io and o-oi. Most important, even for values of P outside this range, the equation provides a continuous method of comparing P values for different samples, as opposed to the tabular interpolation often used. The equation can also be simply converted into a computing program to be used with many desk calculators.
1. Small time errors in the biological clocks of pigeons appear to have no effect on their navigation.
2. An error of 2 h seems to shift the pigeons' orientation as predicted by a sun-compass hypothesis, but 6 h shifts gave initial orientation that was too scattered to analyse.
3. Alteration of the apparent sun altitude with mirrors at the loft was without effect on navigation.
4. The administration of 30 % D20 in the pigeon's drinking water combined with
5. We conclude that the pigeon's navigation is probably not based on either the sun or on accurate sense of time at the home loft.
We are grateful to the many students and colleagues who have assisted in this work. Particularly we thank Norman Budnitz, Alexander Davis, Jerome Hunsaker III, Donald Maclver, Richard Miselis, Douglas Smith, Lee Snyder and Neil Tractman who assisted with the training and tracking and all other aspects of the study. Professor William T. Keeton, Jr., and Mr Andre Gobert generously cared for our experimental pigeons at Cornell. Professor Donald Griffin kindly read and criticized this paper. The research was supported in part by grants from the Committee on Research and Exploration, the National Geographic Society, the National Science Foundation, Grant GB 6777 and the National Institutes of Health, Division of Neurological Diseases and Stroke, Grant Number 5 Roi NS 08708-01.
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HOFFMAN, K. (1958). Repetition of an experiment on bird orientation. Nature, Lond. 181, 1435—7. HOFFMAN, K. (1965). Clock-mechanisms in celestial orientation of animals. In Orcadian Clocks (ed.
J. Aschoff), Amsterdam.
KEETON, W. T. (1969). Orientation by pigeons: is the sun necessary ? Science, N. Y. 165, 922-8. KRAMER, G. (1953). Wird die Sonnenhohe bei der Heimfindeorientierung verwertet ? J. Orn. Lpz.
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APPENDI X TABL E Al l th e release s discusse d i n th e first portio n o f th e pape r ar e tabulate d here . Eac h bir d i s identifie d b y a ban d numbe r an d colou r o f th e band . Th e trac k numbe r refer s t o th e numbe r o f track s afte r training . Th e dat e o f releas e i s give n nex t wit h th e las t digi t o f th e year , i.e . 5 refer s to 1965 . Releas e tim e i s give n i n Easter n Standar d Time . Th e 1 0 mil e bearin g i s th e directio n fro m th e releas e poin t whe n th e pigeo n wa s a t 1 0 mile s fro m th e releas e point . Th e traine d com -pas s bearin g i s th e directio n fro m th e trainin g poin t t o th e hom e loft , an d th e compas s erro r i s th e differenc e betwee n thi s bearin g an d th e 1 0 mil e bearin g fro m th e release . Th e hom e bearin g i s th e directio n o f th e hom e lof t fro m th e releas e point , an d th e hom e erro r i s th e differenc e betwee n thi s bearin g an d th e 1 0 mil e bearin g fro m th e releas e point . Th e nex t colum n indicate s whethe r th e pigeo n a t 1 0 mile s fro m releas e wa s mor e nearl y oriente d towar d th e hom e lof t (H ) o r i n it s traine d compas s directio n (C) . Th e homin g spee d i s give n i n statut e miles/h , an d i s base d o n th e tim e betwee n releas e an d arriva l a t th e loft . Th e lengt h rati o i s th e lengt h o f th e pigeon' s trac k divide d b y th e straigh t lin e distanc e fro m releas e t o home . Th e deviatio n i s a measur e o f ho w fa r th e pigeon' s trac k deviate s fro m a straigh t line . I t i s measure d b y determinin g th e distanc e o f th e trac k fro m a straigh t lin e a t te n equall y space d points . Thes e distance s ar e the n average d an d expresse d a s a percentag e o f th e straigh t lin e distanc e fro m th e releas e poin t t o th e loft . Th e weathe r i s give n i n standar d symbols : O , clear ; ® , scattere d clouds ; OD , broke n clouds ; © , over -cast . Th e C i refer s t o thi n cirrifor m overcas t throug h whic h th e su n wa s visible . Th e visibilit y is i n statut e mile s fro m th e releas e point . Th e win d directio n i s th e directio n fro m whic h th e win d wa s blowing , an d th e velocit y i s i n statut e miles/h . Th e numbe r o f straigh t trac k segment s (STS ) refer s t o th e numbe r o f segment s o f track , 2 0 mile s (3 2 km ) o r mor e long , tha t woul d fit withi n a rectangl e onl y 2 mile s wid e mad e b y eac h pigeo n i n territor y whic h wa s a t leas t 1 0 mile s fro m al l previou s tracks . Th e lengt h o f eac h ST S i s give n i n statut e miles , th e bearin g o f it s lon g axi s an d th e bearin g t o th e hom e lof t a t th e star t o f eac h segment . Th e differenc e betwee n th e bearin g o f th e ST S an d th e directio n t o th e hom e lof t a t th e beginnin g o f th e ST S i s give n a s a 'hom e error' ; th e compas s erro r compare s th e bearin g o f th e ST S wit h th e pigeon' s trainin g direction . Finall y fo r shifte d birds , th e false-hom e erro r expresse s th e differenc e betwee n th e observe d bearin g fro m th e releas e poin t a t 1 0 mile s an d th e bearin g fro m th e releas e poin t t o th e fals e home . Th e lette r a afte r a figure i n th e tabl e mean s tha t th e figure i s a n estimat e base d o n onl y a partia l track . N O TREATMEN T Bird Y 3 ib Y3i b 108 s W Y W Y W Y B7 7 0
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7 10 4 —OO 5 H 26 0 7 09.5 3 1 6 8 +00 3 10 4 +06 7 C 18 7 8-6 2 cf . e n C . o * -O j • < 30 3 19 1 C D 1-2 3 2 7 CD-d 15 5 18 7 £ 2-8 © 1 0 2 19 3 18 3 0 )
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Compass error Home error
Home bearing start of STS
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Home error ' S> ' ~ o o ' o 8 8 o ' J S § ' " o 8 ' o 2 o 81
I I I II
Home bearing i oo i oo oo •* i o o •+ oo i N N O* r *O OO r^ I N -a- I-* o j start of STS t - i o o o o •£ » » ' M o n ' o » n ' r> o« N 2 2
•D • CTC N O | N 0 0 ^ - | N + + O I C ©« O I I - »« O« I ««
B e a r i n g b i b I o t*- «*• m m i ^ oo N NO CO IO N « CO <O _ , _ _ . . . .
O H I C O C O O MHIHI H I 0<O CO«n CO MHI M O O
T e n t r t h S T S I N I O C O M I I O O »« I^* I O r t n i r ^ r ^ c o i c ^ •+ *"* • ) • < $ >
-N O . S T S O H. O M M Q •"! M Ht M O »-• MWQ '- 'H. MO '- ' HI N Q | H "
mt.) « _ • BL E <; H X Q .PPEN ] Wind velocity Wind direction Visibility Sky Deviation Length ratio Homing speed m.p.h. Sra error Home error Home bearing Compass error Trained io mile bearing Release time E.S.T. Year Month Day o o tn e o in Si z
1 "Q o 1
100 o 1 o NO g 11.0 5 «« vi i Lt . 1 Var . b e I.1 Z m O ON NO O CO 0 1
ti n O N d vii i 0 0 m N e I.* I 0 a; Uo 0 0 N ZZ-E l vii i CO S 2 O N e o.t z 0 m O 8 CO NO N 09-3 7 t ^ N m
Ao-NO CO ).Zz % N >n O ° 11 2 0 N CO CO d 0 0 vii i N M NO O O m CO cS 0 Q N §. N * a; zi o ji o NO NO N % 10.5 9 00 IT A O 1 0 O O 0 E. S zV o NO N 02 1 & 6* 0 2 >5 5 1 10.1 2 -.a 8 1 0 ® © * i " a? So o ? 0 3" 10 O 0 0 V 0 0 8 1 O a CO CO 0 0 00 0 60 0 2 m 0 Ez-i o 0 0 • > t n 0 CO w O-C D CO CO <3 CO a; m O Cr it i zn CO M d 0 0 • > 0 CO i n N e Inc . N 1 Inc . Inc . N [nc . : 11.4 9 CO IT A M O O NO CO £ 0 § a N as NO O 12 -CO N $ d-0 CO vii i CO 5 mi n shif t o1 ozt < m 0 0 0 CO N aj Sz o 0
1M CO 09-5 3 CO vi i 0 co O > 20 0 e In c OO O 0 CO e m
1o> 0 a; CO O CO 0 00 0 )4 9 1 So-o i CO vi i N O £fr i « m CO O O 0 0 III A CO 0 0 CO e CO CO 0 N £fo 0 2 CO 10.0 2 0 0 vii i
CO 0 0 0 0 © E.6 E -zV o N O N NO N 09-3 7 UI A CO Ft to 0 0 e 00 io N
1O O NO O O NO oo-E l r-•H t o O O •n O 0 0 0 9" liu a; Ez o 0 Lzi 00 NO _, LvLo x N 0
a0 O -O 1 to CO NO CO NO CO CO 0
.a0 0 n 0 e OZ.E E
*c 0 1 0 0 £* o
10 1 & N SS-o i 10 > N N ? oi z < 00 0 NO * 0 1 i n OI O & 8. CO NO O I O
> > NO M O O NO CO M e Sz.z i i n 0 6* 0
1I I O — j >9 3 i 10.2 1 NO > CO 1 1 1 1 1 1 In c O 0 ** o 0 0 m 00 d 11 1 > -oi z i e
1CO N O 1
JCO 0 1 2 CO 0 00 d NO tn > 0 0 N e i-i Ezi . — 02 0 S-0
i1 ? 0 10.5 3 00 > 0 N Release po
ase J » O H J f e b . O O O O Z ^ > 1 11 1 h fl ft 5 5 = J _ E
-M m -rj- NO NO
APPENDI X TABL E (coitt.) t o u