Magnetic inclination compass: A basis for the migratory orientation of birds in the Northern and Southern Hemisphere

We conducted orientation experiments with Silvereyes,Zosterops lateralis, Australian passerine migrants, to see whether birds living in the Southern Hemisphere in a magnetic field with an upward inclination orient in the same way as birds in the Northern Hemisphere that experience a downward inclination of the magnetic field. Tested indoors in the local geomagnetic field, the birds preferred southerly directions corresponding to their migratory direction in spring. In a magnetic field with a reversed vertical component, they reversed their directional tendencies. This shows that the magnetic compass of Silvereyes also functions as an inclination compass based on the inclination of the field lines instead of the polarity.     

Overcast tests with clock-shifted pigeons

In order to investigate the pigeon's compass mechanism, a series of overcast tests with clock-shifted birds were run at two familiar release sites. While controls were able to assume a correct homeward direction, the experimental birds' initial orientation cannot be explained either on the basis of a time-compensated sun compass or of a time-independent magnetic compass. Speculative explanations of our paradoxical results are attempted.     

The sun compass

Summary The sun compass was discovered by G. Kramer in caged birds showing migratory restlessness. Subsequent experiments with caged brids employing directional training and clock shifts, carried out by Hoffmann and by Schmidt-Koenig, showed that sun azimuth is used and sun altitude ignored. McDonald found the accuracy to be ±3^o–±5^o. According to Hoffmann and to Schmidt-Koenig, caged birds trained at medium northern latitudes were able to allow for the sun's apparent movement north of the arctic circle but not in equatorial and trans-equatorial latitudes.In homing experiments, and employing clock shifts, Schmidt-Koenig demonstrated that the sun compass is used by homing pigeons during initial orientation. This finding supports the existence of a map and compass navigational system. Pigeons living in equatorial latitudes utilize the sun compass even under the extreme solar conditions of equinox (Ranvaud, Schmidt-Koenig, Ganzhorn et al.). The use of the sun compass during zenith passage of the sun is being investigated.     

Ecological causes and consequences of bird orientation

Summary An advanced orientation capability offers possibilities for birds to optimize movement patterns in a wide variety of ecological situations. The adaptive significance of different patterns of angular dispersion and of orientation responses to topography and sociality are elucidated. The orientation capacity is characterized by flexibility, exemplified by reorientation promoting safety and restoration of fat reserves during migration. There are also limitations to the orientation process, leading to costs of migration through mis- or disorientation, and to constraints on the evolution of routes and timing of migratory flights. Young migrants may acquire an erroneous compass sense, and misorient several thousands of kilometers off their normal course. Widespread and dense fog of long duration causes disorientation and mortality among land birds migrating over the sea. Orientational constraints in the evolution of migration routes may be most easily disclosed at high geographic and magnetic latitudes. Here the birds are faced with special difficulties in using their celestial as well as their magnetic compasses. The sun compass could be used for great circle orientation, but observed spring flight trajectories of high arctic shorebirds and geese seem to conform with rhumbline routes.     

Magnetic orientation and celestial cues in migratory orientation

Summary Young birds on their first migration possess innate information on the direction of their migration route. It is present in two forms, using 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, 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.     

A magnetic pulse leads to a temporary deflection in the orientation of migratory birds

Migratory Australian Silvereyes were treated with a strong magnetic pulse designed to alter the magnetization of the small magnetite particles that are found in birds' heads. Prior to the treatment, the birds preferred the northeasterly migratory direction. The pulse initially resulted in a 90° clockwise shift of orientation; however, within about a week, the birds seemed to return to their original headings. These findings, which seem to suggest an involvement of magnetite in migratory orientation, are in contrast with previous findings which indicated that it is a light-dependent process. They are discussed in view of the current concepts on magnetoreception and on the role of magnetic information in avian orientation.     

Magnetic compass orientation in the subterranean rodentCryptomys hottentotus (Bathyergidae)

Summary To test whether mole-ratsCryptomys 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^o or by 180^o, the mole-rats changed their nest position accordingly. This clearly shows that they can use the magnetic field for direction finding.     

Conceptual approaches to avian navigation systems

Summary The general basis of migratory orientation in birds is most probably an endogenous time-and-direction program. Directions are selected with respect to celestial and geomagnetic clues. Using these clues, a bird may reach a large population-specific area; however, it will hardly be able to find a particular location, for instance its previous breeding site. Homing to a familiar site over several hundred kilometres of unfamiliar terrain appears to be based on the smelling of atmospheric trace compounds. Conceptual approaches to the mechanism of olfactory navigation have as yet only reached an early state of speculation.     

Endogenous control as a possible basis for varying migratory habits in different bird populations

Summary In handraised experimental groups of 4 populations ofSylvia atricapilla, it was found that the development of migratory restlessness under constant conditions was a fairly good reflection of the different (typical, partial, and non-) migratory habits of the populations. Thus, the different migratory habits seem to be endogenously preprogrammed and genetic in origin. The results of a preliminary cross-breeding experiment are at least compatible with the assumption that partial migratory habit in the blackcap is due to polymorphism.Supported by the Deutsche Forschungsgemeinschaft; 25th paper of the warbler program of the institute.     

New theories for new instruments: Fabrizio Mordente's proportional compass and the genesis of Giordano Bruno's atomist geometry

The aim of this article is to shed light on an understudied aspect of Giordano Bruno's intellectual biography, namely, his career as a mathematical practitioner. Early interpreters, especially, have criticized Bruno's mathematics for being “outdated” or too “concrete”. However, thanks to developments in the study of early modern mathematics and the rediscovery of Bruno's first mathematical writings (four dialogues on Fabrizio's Mordente proportional compass), we are in a position to better understand Bruno's mathematics. In particular, this article aims to reopen the question of whether Bruno anticipated the concept of infinitesimal quantity. It does so by providing an analysis of the dialogues on Mordente's compass and of the historical circumstances under which those dialogues were written.     

The early history of ship magnetism: The Airy-Scoresby controversy

With the advent of iron-built ships in the early nineteenth century the problem of managing a magnetic compass on board presented considerable difficulty. Prominent among the early scientists who tackled the problem were George Biddell Airy and William Scoresby. Airy had provided a mechanical system, employing correctors in the form of steel magnets and wrought iron masses, by which the ship's magnetic field at the compass position is neutralized. He based his system on the concept that the magnetism acquired by an iron ship during her construction remained with the ship throughout her life. Scoresby, on the other hand, thought differently. After having conducted a thorough and systematic series of experiments on iron plates and bars, he concluded that the magnetic character of an iron ship is liable to sudden and unexpected change. Scoresby argued, therefore, that Airy's system was defective and, indeed, dangerous. The aim of this paper is to discuss the two views which brought Airy and Scoresby into a conflict which is documented in a series of letters to the editor of The Athenaeum.     

Sensory basis of bird orientation

Summary Sensory information which may be essential for the complex process of orientation of birds is described in this article. The use of vibrational, visual, chemical, olfactory, magnetic cues and their receptive mechanisms, as far as they are known, are explained. Special reference is given to the behavioral and physiological aspects of magnetic sensitivity.     

Sensory basis of bird orientation

Sensory information which may be essential for the complex process of orientation of birds is described in this article. The use of vibrational, visual, chemical, olfactory, magnetic cues and their receptive mechanisms, as far as they are known, are explained. Special reference is given to the behavioral and physiological aspects of magnetic sensitivity.     

Iron-sulfur proteins: Recent developments in the field

Summary Iron-sulfur clusters in proteins are now recognized as among the main types of electron-transferring groups in biological systems, besides heme and flavins. Recent developments have brought forth a better understanding about the ways the protein environment modulates the potential of the cluster by placing the cluster in a more or less hydrophobic surrounding. Refinement in models, extensive studies on the kinetics of electron transfer (e.g. by measurement of the electronic spin lattice relaxation time) and the introduction of novel spectroscopic methods (EXAFS, magnetic CD and others) in the elucidation of structures in various systems are among the main developments. Other advances include EPR studies of the spatial orientation of Fe−S centers in complex membraneous systems (e.g. in mitochondria) and the recent elucidation of the nature of center X in photosystem I by M?ssbauer-spectroscopy. M?ssbauer studies have also been described on a number of Fe−S proteins (nitrogenase, aconitase, some ferredoxins, etc.) and revealed the existence of novel structures that enlarged the number of known basic units of Fe−S centers. These advances include: 1. the discovery of a novel non-heme Fe-protein (called desulforedoxin) of the rebredoxin type, 2. the elucidation of the nitrogenase Fe−S centers and the nitrogenase cofactor and 3. the discovery of a three-iron cluster in several enzymes and some ferredoxins. The latter 3-Fe cluster seems capable of being converted into a classical 4-Fe cluster under appropriate conditions, a phenomenon that plays a role in activation-deactivation of some enzymes (e.g. aconitase). It is now recognized that some iron-sulfur clusters may be involved in systems devoided of any oxydation-reduction reaction and may act as sensors of the surrounding redox potential, triggering the activation/deactivation of an enzyme (cf. e.g. aconitase).     

Spatiotemporal programs and genetics of orientation

Summary A number of migratory bird species have endogenous annual rhythms that regulate the entire annual cycle including the migratory portion. Moreover, captive migrants display inherited migratory activity; this could theoretically also be used by free-living migrants as a time-program for migration. Finally, this heritable migratory activity is oriented in a seasonally appropriate direction even in naive birds. These, characteristics should enable inexperienced migrants isolated from contact with experienced conspecifics to utilize a heritable vector-navigation program to migrate from the breeding grounds to the winter quarters. That is, migrants should reach goal areas they have never experienced by migrating in programmed directions, for as long a period as the genetically fixed time-program for migratory activity induces them to do so. The time-course of migration as established by trapping stations, theoretical influences of environmental variables on migratory programs, and also compensatory behavior and migratory backup measures, are discussed. The present evidence supports the view that a large number of migrants are essentially brought to their wintering areas by vector-navigation systems.     

Evolutionary aspects of orientation and migration in birds

Summary Evolutionary aspects of avian migratory orientation and navigation are reviewed. A theoretical approach to the evolution of complex (endogenously programmed) migratory behavior is presented using the comparative method of ordering a progression in existing behavioral characteristics from dispersal, to facultative migration, to obligate migration.     

Biological responses inCaenorhabditis elegans to high magnetic fields

Here we describe a device for testing possible influences of high magnetic fields on biological processes, by which alternating-current magnetic stimuli as high as 1.7 T can be administered. Experiments with a simple multicellular organism, the nematodeCaenorhabditis elegans, revealed that intermittent exposure to the magnetic fields modestly inhibited the animal's reproduction as well as its post-embryonic development, and caused a marked but transient derangement in its locomotory behavior. Available evidence indicates that alternating high magnetic fields can elicit both chronic and acute biological effects, but that the effects may be well tolerated or compensated for by the living organism.     

Advanced optical imaging in living embryos

Developmental biology investigations have evolved from static studies of embryo anatomy and into dynamic studies of the genetic and cellular mechanisms responsible for shaping the embryo anatomy. With the advancement of fluorescent protein fusions, the ability to visualize and comprehend how thousands to millions of cells interact with one another to form tissues and organs in three dimensions (xyz) over time (t) is just beginning to be realized and exploited. In this review, we explore recent advances utilizing confocal and multi-photon time-lapse microscopy to capture gene expression, cell behavior, and embryo development. From choosing the appropriate fluorophore, to labeling strategy, to experimental set-up, and data pipeline handling, this review covers the various aspects related to acquiring and analyzing multi-dimensional data sets. These innovative techniques in multi-dimensional imaging and analysis can be applied across a number of fields in time and space including protein dynamics to cell biology to morphogenesis.     

Selection of biting sites on man by two malaria mosquito species

While searching for blood, female mosquitoes pass through a behavioural process involving responses to visual, physical and chemical properties of the host. Temperature and humidity are thought to dominate mosquito orientation near the host. We observed that biting of two malaria mosquito species, i.e.Anopheles atroparvus (van Thiel) andAnopheles gambiae s.s. (Giles) preferentially occurs on different body regions of a naked motionless human host. Their preference for the head and foot regions respectively correlated with particular combinations of skin temperature and eccrine sweat gland density. Subsequent modification of the host's odour profile by removing exhaled breath and washing feet results in significant changes of these preferences.     

Vues actuelles sur les migrations des Poissons

Summary Mr.Fontaine points to the internal physiologic conditions imposing upon certain species of migratory fishes an amphibiotic character. He mentions the facts suggesting that hyperfunction of the dynamogenic endocrine glands is doubtless one of these conditions, and this interpretation leads him to the question of the permanence of the migratory character of a given species. But according to him this latter seems to be a point in the evolution of a phylum corresponding to the apogee of an orthogenese, itself connected with the evolution of an endocrine activity reaching its culminating point in the species under view. Mr.Fontaine considers then the development of these species: return to holobiose and sedentarity or vanishment. Considering the facts actually known, the two destinies seem possible and in certain cases perhaps successive.