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Results for “Stars, Celestial”

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27 records · Page 2Linked to original sources

PubMed1980

The effect of celestial cues on the ontogeny of non-visual orientation in the garden warbler (Sylvia borin).

It was the aim of this study to find out whether additional information from the sun and the stars during early development leads to an improvement in the young birds' non-visual orientation performance during their first autumn migration period. The results indicate that the birds' ability to determine their migratory direction can mature independently of celestial information. Celestial cues, however, appear to be involved in the normal maturation process of migratory orientation, since the availability of celestial information during ontogeny tends to impair the birds' non-visual orientation.

Age Factors↗

PubMed2001

Ancient chronology. Astronomical orientation of the pyramids.

Spence speculates that Egypt's pyramid builders found true north by using a plumb line: when the stars Kochab and Mizar were seen on the same vertical, one was facing north. As evidence in support of this hypothesis, she points to the proposed interstar-line precession past the north celestial pole at a rate of 27' per century (cy). We argue that a mathematical error affects this result, which when corrected points more strongly to a different pair of stars. This suggests that the conventional ancient chronology, instead of being compressed, may actually have to be expanded slightly.

Journal Article↗

PubMed2006

Calibration of magnetic and celestial compass cues in migratory birds--a review of cue-conflict experiments.

Migratory birds use multiple sources of compass information for orientation, including the geomagnetic field, the sun, skylight polarization patterns and star patterns. In this paper we review the results of cue-conflict experiments designed to determine the relative importance of the different compass mechanisms, and how directional information from these compass mechanisms is integrated. We focus on cue-conflict experiments in which the magnetic field was shifted in alignment relative to natural celestial cues. Consistent with the conclusions of earlier authors, our analyses suggest that during the premigratory season, celestial information is given the greatest salience and used to recalibrate the magnetic compass by both juvenile and adult birds. Sunset polarized light patterns from the region of the sky near the horizon appear to provide the calibration reference for the magnetic compass. In contrast, during migration, a majority of experiments suggest that birds rely on the magnetic field as the primary source of compass information and use it to calibrate celestial compass cues, i.e. the relative saliency of magnetic and celestial cues is reversed. An alternative possibility, however, is suggested by several experiments in which birds exposed to a cue conflict during migration appear to have recalibrated the magnetic compass, i.e. their response is similar to that of birds exposed to cue conflicts during the premigratory season. The general pattern to emerge from these analyses is that birds exposed to the cue conflict with a view of the entire sunset sky tended to recalibrate the magnetic compass, regardless of whether the cue conflict occurred during the premigratory or migratory period. In contrast, birds exposed to the cue conflict in orientation funnels and registration cages that restricted their view of the region of sky near the horizon (as was generally the case in experiments carried out during the migratory season) did not recalibrate the magnetic compass but, instead, used the magnetic compass to calibrate the other celestial compass systems. If access to critical celestial cues, rather than the timing of exposure to the cue conflict (i.e. premigratory vs migratory), determines whether recalibration of the magnetic compass occurs, this suggests that under natural conditions there may be a single calibration reference for all of the compass systems of migratory birds that is derived from sunset (and possibly also sunrise) polarized light cues from the region of sky near the horizon. In cue-conflict experiments carried out during the migratory season, there was also an interesting asymmetry in the birds' response to magnetic fields shifted clockwise and counterclockwise relative to celestial cues. We discuss two possible explanations for these differences: (1) lateral asymmetry in the role of the right and left eye in mediating light-dependent magnetic compass orientation and (2) interference from the spectral and intensity distribution of skylight at sunset with the response of the light-dependent magnetic compass.

Animal Migration↗

PubMed1997

The direction of celestial rotation influences the development of stellar orientation in young garden warblers (Sylvia borin)

The study presented here was conducted in order to analyze the role of the direction of celestial rotation in the development of stellar orientation in young migratory birds. The test birds were garden warblers, Sylvla borin, which leave their breeding ground on a southwesterly compass course. The birds were hand-raised and, during the premigratory period, exposed to an artificial 'sky' in the local geomagnetic field. For the control group C, the star pattern was rotating in the natural direction, with the centre of rotation and magnetic North coinciding. For the three experimental groups, the star pattern was rotating in the opposite direction; for group E1, the centre of rotation coincided with magnetic North, for group E2 the centre of rotation was at magnetic West and for group E3 it was at magnetic East. During autumn migration, the birds were tested without magnetic information under the same, now stationary, sky. All four groups were able to use stellar information for orientation, but only the control group preferred the normal southwesterly course. The three experimental groups, in contrast, all oriented towards a significantly different direction, preferring due south. The results for group E1 showed less scatter than those for the other two experimental groups. These results indicate that the direction of celestial rotation is crucial for the development of the normal migratory course with respect to the stars in young garden warblers. Establishing the species-specific southwesterly migratory course requires an interaction between celestial rotation and magnetic cues; this interaction appears to depend on the natural direction of celestial rotation. Rotation in the reverse direction allowed the birds to respond only in a manner that oriented them away from the centre of rotation.

Journal Article↗

PubMed1991

The development of migratory orientation mechanisms.

Recent experimental studies (since ca. 1985) on the ontogeny of orientation mechanisms in migratory birds are reviewed. The processes and interactions are synthesized into a framework that may help identify critical research questions. Birds that grow up in the earth's magnetic field develop the ability to perform appropriate migratory orientation, even in the absence of any experience with relevant visual cues. In two species, large changes in direction during the course of migration seem to be controlled by an endogenous time program. In one of these, the Pied Flycatcher (Ficedula hypoleuca), the correct magnetic orientation seems to occur only when the magnetic fields appropriate to the latitudes encountered en route were experienced at the proper seasonal time. The magnetic compass may be modified by visual experience with either the day or night sky. Celestial rotation may be the calibrating reference in this case, as it is in the development of the star compass. Young Savannah Sparrows (Passerculus sandwichensis) learn to perform compass orientation at sunset based on polarized skylight. This compass capability seems to be calibrated by magnetic directions. Some problems of experimental design and the interpretation of results from experiments on development are discussed.

Animals↗

PubMed1989

The registered distance of the celestial sphere: some historical cross-cultural data.

Estimates of the diameters of the sun and moon expressed in centimetres have been reported by several authors in the past. These estimates imply that the sizes of the sun and moon are perceived as if these bodies are only some tens of metres distant. In this study five units of length that were used by ancient astronomers to estimate arcs on the celestial sphere were investigated. The purpose was to determine whether the lengths and angles represented by these units imply a specific registered distance of the star sphere. The sizes of the Babylonian cubit, Arab fitr and shibr, Greek eclipse digit, and Chinese chang support the conclusion that the registered distance of the stars was about 10 to 40 metres in these four cultures over the last two millennia.

Astronomy↗

PubMed2001

Migrating songbirds tested in computer-controlled Emlen funnels use stellar cues for a time-independent compass.

This paper investigates how young pied flycatchers, Ficedula hypoleuca, and blackcaps, Sylvia atricapilla, interpret and use celestial cues. In order to record these data, we developed a computer-controlled version of the Emlen funnel, which enabled us to make detailed temporal analyses. First, we showed that the birds use a star compass. Then, we tested the birds under a stationary planetarium sky, which simulated the star pattern of the local sky at 02:35 h for 11 consecutive hours of the night, and compared the birds' directional choices as a function of time with the predictions from five alternative stellar orientation hypotheses. The results supported the hypothesis suggesting that birds use a time-independent star compass based on learned geometrical star configurations to pinpoint the rotational point of the starry sky (north). In contrast, neither hypotheses suggesting that birds use the stars for establishing their global position and then perform true star navigation nor those suggesting the use of a time-compensated star compass were supported.

Animal Migration↗

PubMed1996

The geographical scale factor in orientation of migrating birds

Migration routes of birds throw light on orientation performance at different geographic scales, over distances ranging from a few kilometres to more than 104 km. Detailed knowledge about the flight routes may be used to test predictions about optimal orientation according to theoretical principles and about the use of compasses based on celestial or magnetic cues. Ringing recoveries demonstrate that the migratory journey of many species, such as the wheatear and willow warbler, is divided into successive legs with different main orientation. Autumn and spring migration routes are often different, sometimes diverging on a continental scale. Aerial radiotracking of whooping cranes in North America and satellite tracking of brent geese migrating from Iceland across the Greenland ice cap point to the significant role of large-scale topography for the shaping of migration routes. Compass and position control are also required, e.g. during long passages across featureless sea or ice, but how these elements are integrated into the birds' orientation system remains unclear. Radar studies from the Arctic Ocean illustrate the importance of map projections for interpreting flight paths and suggest that birds accomplish approximate great circle orientation. Gradual course changes shown by migrating knots monitored by radar in Scandinavia are at variance with expected changes if the birds were to use a star, sun or magnetic compass over longer distances. Accurate recording of short flight segments shows how flying birds respond to visual, audible and electromagnetic cues, and also documents orientation precision and capacity to integrate rapidly shifting courses into a consistent resulting orientation. Analyses of flight patterns are crucial for understanding how birds find and follow their migration routes over different ranges of geographical scale.

Journal Article↗

PubMed2000

Magnetic information calibrates celestial cues during migration.

Migratory birds use celestial and geomagnetic directional information to orient on their way between breeding and wintering areas. Cue-conflict experiments involving these two orientation cue systems have shown that directional information can be transferred from one system to the other by calibration. We designed experiments with four species of North American songbirds to: (1) examine whether these species calibrate orientation information from one system to the other; and (2) determine whether there are species-specific differences in calibration. Migratory orientation was recorded with two different techniques, cage tests and free-flight release tests, during autumn migration. Cage tests at dusk in the local geomagnetic field revealed species-specific differences: red-eyed vireo, Vireo olivaceus, and northern waterthrush, Seiurus noveboracensis, selected seasonally appropriate southerly directions whereas indigo bunting, Passerina cyanea, and grey catbird, Dumetella carolinensis, oriented towards the sunset direction. When tested in deflected magnetic fields, vireos and waterthrushes responded by shifting their orientation according to the deflection of the magnetic field, but buntings and catbirds failed to show any response to the treatment. In release tests, all four species showed that they had recalibrated their star compass on the basis of the magnetic field they had just experienced in the cage tests. Since release tests were done in the local geomagnetic field it seems clear that once the migratory direction is determined, most likely during the twilight period, the birds use their recalibrated star compass for orientation at departure. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗