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Biomedical subjects

R Wiltschko

Publications and source records attributed to R Wiltschko.

17 recordsLinked to original sources
PubMed1999

Staying in plastic containers interferes with the orientation of clock-shifted homing pigeons.

Staying in plastic containers ventilated with natural air during transport and while waiting at the release site was found to affect the initial orientation of pigeons, Columba livia f. domestica, that were exposed to a 6-h clock-shift. The deflection from the mean direction of controls was significantly smaller, and the mean vector length was significantly shorter, than that of clock-shifted pigeons transported in conventional wooden cages. This effect was most pronounced when the birds stayed in plastic containers for the first and second time. Nonshifted control birds seemed to be largely unaffected by plastic containers. There was no influence on homing performance, which suggests a transient nature of the effect. Since the clock-shifted birds had access to the same orientational cues as the controls, we suggest that their sun compass was impaired by stress. We discuss general implications of this container effect, particularly in relation to some cases of olfactory deprivation where containers have been used and stress-induced side-effects cannot be excluded. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Effect of a magnetic pulse on the orientation of silvereyes, zosterops l. lateralis, during spring migration

The orientation behaviour of Australian silvereyes, Zosterops l. lateralis, was tested during their spring migration, when they head southward to their Tasmanian breeding grounds. With only the local geomagnetic field as a cue, the birds significantly preferred their normal southerly migratory direction. Treatment with a short, strong magnetic pulse designed to alter the magnetization of single-domain magnetite led to a significant deflection towards the east for the next 4 days. This was followed by a period of non-oriented behaviour. From day 10 onwards, the birds returned to their original southerly headings. Together with previous findings, these data suggest that the navigational 'map' of these birds includes magnetic parameters and that a magnetite-based receptor provides them with information about their position. The transient nature of the effect is not easily explained on the basis of single-domain magnetite.

Journal Article↗
PubMed1996

Magnetoreception: why is conditioning so seldom successful?

Conditioning is a highly successful method for analyzing the sensory capacities of animals. With magnetic stimuli, however, it does not seem to work: negative results by far outnumber the positive ones. This is true for cardiac and operant conditioning as well as for directional training. The reasons for these failures are largely unclear. They may stem from the function of the magnetic field as orientation cue and from the fact that the magnetic field never undergoes a rapid change in nature, which means that animals might not be adapted to respond to such changes. Moreover, since the magnetic field contains directional information, animals might evade the problems arising from self-produced movements by calling on magnetic information only when needed for orientation. In view of this, conditioning does not appear to be a suitable technique for testing magnetic sensitivity.

Animals↗
PubMed1996

The function of olfactory input in pigeon orientation: does it provide navigational information or play another role?

In 1972, Papi and his colleagues reported that anosmic pigeons were severely impaired in orientation and homing performance. This observation was followed up in a series of experiments involving numerous elaborate experimental manipulations. On the basis of their results, the hypothesis of olfactory navigation was proposed. Attempts to replicate these findings at other lofts produced widely differing effects, which suggested a highly variable role of olfaction. However, meteorological data, as well as certain other aspects of the findings, throw doubt on the role of odours as navigational cues. (1) Odours of the required characteristics and distribution do not seem to exist. (2) Some effects of 'olfactory' manipulations do not seem to depend on the availability of odours. (3) Olfactory treatments proved mostly effective, but often the effect was not as predicted. In view of these findings, explanations other than olfactory orientation cannot be excluded; accepting olfactory input as navigational information seems premature. Some of the findings are in agreement with the assumption that olfactory manipulations impair the birds' general processing and integration of information in some unknown way.

Journal Article↗
PubMed1996

Magnetic orientation in birds

The magnetic field of the earth is an omnipresent, reliable source of orientational information. A magnetic compass has been demonstrated in 18 species of migrating birds. In all species studied with regard to its functional properties, it was found to be an 'inclination compass', i.e. the birds derive directional information from the inclination of the field lines, and thus distinguish between 'poleward' and 'equatorward' rather than 'north' and 'south'. Such a mechanism means that birds from the northern and southern hemisphere may rely on the same migratory programme. Long-distance migrants, however, face the problem that their magnetic compass gives bimodal information at the magnetic equator. Transfers of information between the magnetic field and celestial sources of directional information have been demonstrated; the two systems interact in a complex way. The data on the use of magnetic parameters for position finding are less clear. The experiments involve releases of homing pigeons; correlations of their orientation with natural variations in the magnetic field and the effects of magnetic manipulation reveal an enormous variability. The role of magnetic parameters in the multifactorial navigational system is poorly understood.

Journal Article↗
PubMed1991

Orientation in birds. Magnetic orientation and celestial cues in migratory orientation.

Young birds on their first migration possess innate information on the direction of their migration route. It is represented twice, using both celestial rotation and the geomagnetic field as references. These two systems, together with information provided by factors associated with sunset, interact in a complex way to establish the migratory direction. During ontogeny, celestial rotation appears to be dominant; during migration, however, celestial cues appear to be controlled by the magnetic field.--The factors associated with sunset--the view of the setting sun and the characteristic pattern of polarized light--are important secondary cues which seem to derive their directional significance from the magnetic field. Their role appears to be more variable, with possible species-specific differences. During spring migration and later autumn migrations, flying in the migratory direction is complemented by navigational processes which enable the birds to return to a specific home site known from previous stays.

Animals↗
PubMed1990

Magnetic compass orientation in the subterranean rodent Cryptomys hottentotus (Bathyergidae).

To test whether mole-rats Cryptomys hottentotus were able to use the magnetic field for orientation, laboratory experiments were conducted which were based on the animals' spontaneous tendency to build their nests at the same position in a circular arena. In the local geomagnetic field, the animals preferred the SE-sector. When magnetic north was turned by 120 degrees or by 180 degrees, the mole-rats changed their nest position accordingly. This clearly shows that they can use the magnetic field for direction finding.

Animals↗
PubMed1985

Pigeon homing: does initial orientation include a 'preferred compass direction'?

To find out whether the initial orientation of pigeons is affected by a spontaneous directional tendency, as postulated by Wallraff's (1974, 1978, 1982) hypothesis, experienced birds were released at test sites distributed symmetrically around their loft. The length of the mean vectors of the single releases, the deviations from the home direction, the homeward components as well as the homing speed did not show a correlation with the geographic position of the home direction. Summarizing four sites each on 21 experimental circles, we frequently obtained significant compass vectors, but they varied in direction between 115 degrees ESE and 351 degrees N, depending on what sites had been used, and did not indicate a uniform trend. A 'preferred compass direction' as an integrated part of pigeon navigation, being the reason for the frequently observed deviations from the home direction, could not be confirmed. The problematic nature of simply pooling the data of several symmetrically distributed test sites and calling any resulting significant vector a 'preferred compass direction' is discussed, together with other possible reasons for asymmetrical distributions of release site biases.

Age Factors↗
PubMed1981

Pigeons with a deficient sun compass use the magnetic compass.

Homing pigeons that had never seen the sun before noon could not use the sun compass in the morning; nevertheless they were homeward oriented. When such birds carried magnets, however, they were disoriented, suggesting they were using a magnetic compass. These findings indicate that the magnetic compass is available to pigeons whether or not the sun compass has been established and that the magnetic compass is apparently the first source of compass information.

Animals↗
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↗
PubMed1975

The interaction of stars and magnetic field in the orientation system of night migrating birds. I. Autumn experiments with European Warblers (gen. Sylvia).

In the autumn migration periods of 1971, 1972, and 1973 the orientation behavior in registration cages of Sylvia communis, S. borin and S. cantillans was analyzed to find out what relative importance the birds assign to information from the stars and from the magnetic field for direction finding. We obtained the following results: 1. Under clear sky in the local earth's magnetic field (Control) the warblers showed directional preferences that corresponded to their expected migratory direction based on ringing recoveries. 2. When magnetic north was turned by 120 degrees to ESE (Test), all three species preferred on clear nights their migratory direction according to the magnetic field, in spite of contradicting information from the stars. 3. In a partly compensated magnetic field, which could not be used for orientation any more, no significant directional preference could be observed, although the stars were visible. Dividing these data into two groups according to whether the birds had been tested in Control or Test previously, we found a tendency for the directions selected here to depend upon the north direction of the magnetic field during the bird's previous tests. From this and from the observation that the concentration of orientation behavior decreases in the absence of stars, we derive the following orientational model: The magnetic field provides the primary directional information for migrating birds. The stars do not contain directional information in themselves, but they can become secondary sources of orientation when information from the magnetic field has been transferred to them previously. The importance of this mechanism lies in making it easier for the birds to maintain their migratory direction. The ecological advantages of such a system are discussed and critically compared to the other models of star orientation.

Animals↗
PubMed1975

The interaction of stars and magnetic field in the orientation system of night migrating birds. II. Spring experiments with european robins (Erithacus rubecula).

To investigate the relative importance of stellar and magnetic cues for the compass orientation of night migrating birds, 45 European robins (Erithacus rubecula) were tested in automatically registering cages with view of the clear natural night sky. One group was tested in the natural local geomagnetic field, the other group in a field pointing to 120 degrees ESE; birds from both groups were additionally tested in a magnetic field the horizontal component of which was compensated. The observed orientation behavior leads to the conclusion that star compass and magnetic compass are not independent, but that they are interlinked in the way that the star compass is established by information from the magnetic compass.

Animals↗