William T. Keeton

The Orientational and Navigational Basis of Homing in Birds

Publisher Summary This chapter discusses the orientational and navigational basis of homing in birds. Modern-day homing pigeons that are the products of centuries of intense selection for the sort of behavior are considered. Review of the records of hundreds of pigeon races shows that the limitation on the distances from which pigeons can successfully home is primarily a function of the physical hardships involved rather than of orientation capabilities. Three different types of orientational ability are discussed. Type I, usually called piloting, is steering a course on the basis of familiar landmarks. Type II is the ability to head in a given compass direction without reference to landmarks. Type III, the most complex, is true navigation, which is the ability to orient toward a goal, regardless of its direction, by means other than recognition of landmarks. The possibility that the earths magnetic field may provides directional information to an orienting bird. Yeagleys hypothesis is discussed, which explains that the flying bird could detect the geographic variations in both the vertical component of the magnetic field and the strength of the Coriolis force. A hypothesis of complete navigation by the sun alone was suggested by Matthews according to which a displaced bird could determine its latitudinal displacement by observing the suns movement in arc and extrapolating that arc to its noon position; comparison of the suns noon altitude at the release site with its noon altitude at home would indicate whether the bird was north or south of home, and how far. Kramers Map-And-Compass Model is discussed, which shows many birds, including pigeons, can use the sun as a compass. The chapter also discusses the recent discoveries concerning possible orientational cues and shortcomings of the homing process.

Orientation by Pigeons: Is the Sun Necessary?

Although most recent hypotheses of pigeon homing have assigned an essential role to the sun, there has been some evidence suggesting that the sun is not essential. Two series of releases were designed to examine the question more carefully. Birds whose internal clocks had been shifted 6 hours were used in the critical tests. Under sun, the vanishing bearings of the clock-shifted birds were deflected in the direction predicted by a hypothesis of use of the sun as a simple compass. By contrast, under total overcast the bearings of both the clock-shifted and the control birds were homeward oriented and there was no difference between them, even at a release site the birds could never have seen previously. Therefore it is concluded that the sun is used as a compass when it is available, but that the pigeon navigation system contains sufficient redundancy to make accurate orientation possible in the absence of both the sun and familiar landmarks; the orientational cues used under such conditions do not require time compensation. This conclusion is in complete disagreement with the Matthews sun-arc hypothesis of pigeon navigation, and it makes necessary a major reformulation (at the very least) of the other principal hypothesis, that of Kramer.

Release-site bias as a possible guide to the “map” component in pigeon homing

SummaryIn an attempt to learn more about the so-called “map” component in pigeon navigation, nine series of tests comprising 34 test releases were performed at a release site, 89 miles NNE of Ithaca, New York, where Cornell pigeons regularly depart nonrandomly but with a large clockwise deviation from the true home direction. The tests included releases of: (1) experienced pigeons new to the site, under sun; (2) pigeons with previous experience at the site, under sun; (3) experienced pigeons new to the site, under total overcast; (4) pigeons with previous experience at the site, under total overcast; (5) first-flight youngsters, under sun; (6) directionally trained pigeons; (7) pigeons from two other Ithaca-area lofts; (8) pigeons from two more distant lofts; (9) Bank Swallows from an Ithaca colony; (10) clock-shifted pigeons; (11) radio- and airplane-tracked pigeons.The results of these tests indicate that the directional bias of the Cornell pigeons is, in general, not dependent on weather conditions or on the previous experience of the birds. Moreover, a similar bias is shown by both pigeons from other Ithacaarea lofts and Bank Swallows from Ithaca. And a similar bias from their respective home directions is shown by birds from other areas. Clock-shifted pigeons departing more directly toward home have poorer homing success than controls. It is concluded that some environmental factor basic to the avian homing process is rotated clockwise at this release site, that biologically the birds are not making an “error” but are probably reading correctly a distorted map.

Detection of polarized light by the homing pigeon,Columba livia

SummaryOf 12 homing pigeons tested, four could be trained to discriminate between a linearly polarized light source with a rotating axis of polarization and the same light source with a stationary axis of polarization. Initially, all 12 pigeons were trained to discriminate between rotating and nonrotating crosshairs. The crosshairs were gradually faded until only polarized light remained. The response was a classically conditioned increase in heart rate. An additional control series was performed using neutral density filters. This is the first evidence for polarized light detection in birds.

Detection of changes in atmospheric pressure by the homing pigeon,Columba livia

SummaryHoming pigeons were tested for their ability to detect air pressure changes in an otherwise constant environment chamber. Ten of 12 birds tested did respond to the pressure changes. The 50% threshold of detection was 10 mm H2O or less, which is approximately equivalent to a change in altitude of 10 m or less. Performance was better in a chamber with artificial background noise than in an abnormally quiet chamber.

Attempts to condition homing pigeons to magnetic stimuli

SummaryNinety-seven homing pigeons were tested for their ability to detect small changes in magnetic fields. The tests, which were intended to corroborate and extend those reported by Reille (1968), were performed in uniform magnetic fields using 2 m diameter Helmholtz coils (series I), and also in non-uniform fields using 24 cm diameter coils (series II). There were no significant differences between responses to magnetic fields and control tests, though significant responses to a light flash demonstrated the overall viability of the test method, which was a classically conditioned increase in heart rate. In series I there were indications of a difference between two magnet treatments, steady fields vs. alternating fields, but in a more sensitive test for the same effect in series II no differences were observed.

Growing up in an altered magnetic field affects the initial orientation of young homing pigeons

SummaryTo test whether the sun compass of pigeons is calibrated by the magnetic field, a group of young pigeons was raised in an altered magnetic field in which magnetic north was turned ca. 65o (in 1974 and 1975) and 120o (in 1980) clockwise. They could see the sun only in an abnormal relation to the magnetic field, since they were released for exercise flights or training flock tosses only when the sky was totally overcast.On their first flight in sunshine these experimental birds deviated clockwise from the mean of their controls; the amount of this deviation was, however, only about half of the shift in magnetic north. On their second flight in sunshine the clock-wise deviation changed to counterclockwise. This change occurred after an exercise flight in sunshine as well as after a homing flight. On later flights in sunshine the differences in orientation between experimentals and controls seemed to disappear.These findings indicate that the magnetic compass is involved in the learning process to establish the sun compass, but the relation between the two systems is more complex than the calibration hypothesis assumed.

Effect of Outward Journey in an Altered Magnetic Field on the Orientation of Young Homing Pigeons

To test whether magnetic directional information gained during the outward journey is incorporated in determining the home direction after displacement, young homing pigeons were transported to the release site in an artificially altered magnetic field. Controls were transported in a separate vehicle; a third group of birds was transported together with the controls, but after arriving at the release site, they were placed in the altered field for a period equal to the duration of the journey.

The effect of a “permanent” clock-shift on the orientation of experienced homing pigeons

SummaryA group of experienced homing pigeons vas subjected to a 6 h slow shift of their internal clock and kept under these conditions for more than 2 months. During the overlap time between the natural and artificial photoperiods they were released for training flights to familiarize them with an area while living in a “permanent shift”.Tested outside the permanent shift training range, the experimentals always deviated about 30° clockwise from the mean of their controls, markedly less than in a regular 6 h slow shift. Inside the permanent shift training range, however, they oriented like the controls (Fig. 2). When their internal clock was returned to normal, the birds showed a larger counterclockwise deflection on their first flight, which was roughly comparable to the effect of a regular 6 h fast shift (Fig. 3). On later flights after normalization, this large shift was no longer found; instead we observed a roughly 30° counterclockwise deflection when they were released inside the permanent shift training range in the morning. This deflection did not seem to occur in the afternoon or outside the permanent shift training range (Figs. 4, 5), and it disappeared when the birds were repeatedly released from the same site (Fig. 6).The occurrence or non-occurrence of the deflection was independent of the duration of the shift or the time passed after normalization; it seemed to depend solely on whether the birds had become familiar with a given site in the situation of the “permanent” shift. This argues against an effect based on the sun compass. We tend to assume that the still unknown navigational “map” is involved. In this case, however, as the deflection is independent of the home direction and the type of release site bias, the factors in question would act very differently from the gradients on which the traditional concepts of the navigational “map” are based. The processes establishing and updating the “map” and their possible differences are discussed.

Distance effect in pigeon orientation: an evaluation.

1. Matthews (1955, 1963), Schmidt-Koenig (1964, 1966, 1968), and Wallraff (1967) have reported that pigeons orient toward home best when released close to the loft or at a long distance from it; they report poor orientation at intermediate distances, and suggest that this has important implications for the nature of the navigational system used by birds.2. We have failed to detect any such distance effect in 172 test releases utilizing 2525 single-tossed pigeons from the Cornell lofts. When the homeward component is plotted against distance, we obtain dissimilar curves for the four cardinal directions. Furthermore, the values of the homeward component may be quite different at two release sites approximately the same distance and direction from the loft.3. We obtained particularly good orientation at the intermediate distances where, according to the distance effect, it should be poorest. This was true not only of experienced birds but also of first-flight youngsters.4. Analysis of our data, as well as re...