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ANIMAL BEHAVIOR: CHICKENS ORIENTING TO THE GEOMAGNETIC FIELD

The following points are made by R. Freire et al (Current Biology 2005 15:R620):

1) Although behavioral experiments show that a wide range of animals use the Earth's magnetic field as a compass for orientation, evidence from conditioning experiments has proved elusive [1]. In birds, the only two successful attempts of operant conditioning to magnetic stimuli [2,3] both involved magnetic anomalies rather than changes in magnetic direction. By using the young domestic chick's motivation to locate a hidden social stimulus [4], the authors report they have demonstrated the first conditioned magnetic compass response in birds and show that the ability to orient using magnetic cues has been retained after thousands of years of domestication [5].

2) Eight layer-strain domestic chicks were imprinted on a red table tennis ball and subsequently trained to locate this ball hidden behind one of four screens in the north, east, south or west corners of a square arena. Each chick was released in the center of the arena to search for the ball that had been hidden behind one of the screens. After finding the ball and remaining with it for one minute (reward), the chick was returned to the home pen while the arena was rotated. The chick was re-introduced after approximately 2-5 minutes into the arena for the next trial to locate its reward. Training continued until the chick approached the ball without deviation in three consecutive training trials (criterion). Unrewarded tests -- no ball hidden behind screen -- followed, in which the authors recorded the direction of the first screen that the chick walked behind.

3) Chicks received five tests in each of three conditions: first, the local geomagnetic field (control tests; 56000 nT, -62 deg inclination); second, an experimental magnetic field with magnetic North shifted by 90 deg clockwise to geographic East (shifted-north tests); and third, a field with the vertical component inverted, resulting in an inclination of +62 deg (inclination tests). These tests were presented in a random order and separated by one successful training trial. Training and the 15 tests took 2-4 days for each chick; the chicks were subjected to this procedure twice, at 10-14 and again at 19-23 days post-hatching (hence age was a within-subject factor in the analysis). Chicks reached criterion in 10-22 training trials and required on average 2.0 +- 0.18 training trials between tests during the first testing period, and reached criterion in 5-11 training trials and required on average 1.7 +- 0.16 training trials between tests during the second testing period.

4) The two previous successful studies [2,3] used strong anomalies as stimuli, so that it remained unclear which magnetic parameter -- change in intensity, local gradients, or local changes in direction -- caused the conditioned response. By using a social reward rather than a food reward, we could induce a strong directional tendency and thus demonstrate the first conditioned magnetic compass response in an avian species. Domestic chickens belong to an ancient lineage of birds, separated from the more modern birds already in the cretaceous period. Their having a magnetic compass is of interest also from the phylogenetic point of view, in particular, as they are largely ground-living, normally not covering larger distances. At the same time, the persistence of this mechanism after thousands of years of domestication [5] is remarkable and emphasizes the important role of magnetic compass orientation even in non-migratory species.

References (abridged):

1. Wiltschko, R. and Wiltschko, W. (1995)

2. Bookman, M.A. (1977). Sensitivity of the homing pigeon to an Earth-strength magnetic field. Nature 267, 340-342

3. Mora, C.V., Davison, M., Wild, J.M., and Walker, M.M. (2004). Magnetoreception and its trigeminal mediation in the homing pigeon. Nature 432, 508-511

4. Vallortigara, G., Regolin, L., Rigoni, M., and Zanforlin, M. (1998). Delayed search for a concealed imprinted object in the domestic chick. Anim. Cogn. 1, 17-24

5. Fumihito, A., Miyake, T., Takada, M., Shingu, R., Endo, T., Gojobori, T., Knodo, N., and Ohno, S. (1996). Monophylectic origin and unique dispersal patterns of domestic fowls. Proc. Natl. Acad. Sci. USA 93, 6792-6795

Current Biology http://www.current-biology.com

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NATURAL HISTORY: ON THE MAGNETIC COMPASS OF SONGBIRDS

The following points are made by W.W. Cochran et al (Science 2004 304:405):

1) Billions of songbirds migrate between continents twice each year, but their orientation capabilities are almost exclusively studied in the laboratory. The authors presented birds with experimentally altered orientation cues and followed their subsequent migratory flights in the wild. Avian navigation capabilities are very precise (1), with many individuals returning to the same breeding sites year after year (1-3) after a voyage of up to 25,000 km (4, ).

2) Migratory songbirds can orient on the basis of compass information from the sun and its associated polarized light patterns, the stars, the earth's magnetic field, and the memorization of spatial cues en route. However, the interactions and relative importance of these cues remain unclear and a source of much debate. Our knowledge about the orientation mechanisms of songbirds relies almost exclusively on data from cue-manipulated captive migrants tested in various orientation cages, on vanishing bearings based on the first few hundred meters of flight, and to a much lesser degree on field data (ringing and radar and visual observations) from unmanipulated natural migrants.

3) On clear evenings, the authors fitted Catharus thrushes with radio transmitters and placed them in outdoor cages in an artificial eastward-turned magnetic field from about sunset until the sun was 11 deg or more below the horizon when they were set free. The authors then radio-tracked the birds in flight to obtain heading data. Because Catharus thrushes do not compensate for wind drift but individuals maintain nearly constant preferred headings from night to night, the authors used measured headings for orientation analyses.

4) In summary: Night migratory songbirds can use stars, sun, geomagnetic field, and polarized light for orientation when tested in captivity. The authors studied the interaction of magnetic, stellar, and twilight orientation cues in free-flying songbirds. The authors exposed Catharus thrushes to eastward-turned magnetic fields during the twilight period before takeoff and then followed them for up to 1100 kilometers. Instead of heading north, experimental birds flew westward. On subsequent nights, the same individuals migrated northward again. The authors suggest that birds orient with a magnetic compass calibrated daily from twilight cues, and that this could explain how birds cross the magnetic equator and deal with declination.

References (abridged):

1. P. Berthold, E. Gwinner, E. Sonnenschein, Eds., Avian Migration (Springer, Berlin, 2003)

2. J. P. Hoover, Ecology 84, 416 (2003)

3. P. O. Dunn, D. W. Winkler, Proc. R. Soc. London Ser. B. 266, 2487 (1999)

4. D. C. Outlaw, et al., Auk 120, 299 (2003)

5. W. L. Engels, Biol. Bull. 123, 94 (1962)

Science http://www.sciencemag.org

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ZOOLOGY: ON ANIMAL NAVIGATION

The following points are made by James L. Gould (Current Biology 2004 14:R221):

1) Nearly all animals move in an oriented way, but navigation is something more: the directed movement toward a goal, as opposed to steering toward or away from, say, light or gravity. Navigation involves the neural processing of sensory inputs to determine a direction and perhaps distance. For instance, if a honey bee were to seek food south of its hive, it would depart from home with the sun to its left in the morning, but to its right in the afternoon.

2) Several trends reflecting favorably on natural selection and poorly on human imagination characterized early studies of navigation. One tendency was the assumption that animals sense at most the same cues as we do. Thus, being blind to our own blindness, it came as a total surprise when honey bees and many other species were found to be able to see UV light. As navigation depends on the processing of such cues, the number of "new" senses uncovered in the past fifty years has greatly expanded our thinking about what may be going on in the minds of animals -- and there is no reason to assume the list is complete. To UV must be added polarized light, infra-red light, special odors (pheromones), magnetic fields, electric fields, ultrasonic sounds and infrasonic sounds.

3) The second crippling propensity is what navigation pioneer Donald Griffin called our innate "simplicity filter": the desire to believe that animals do things in the least complex way possible. Experience, however, tells us that animals whose lives depend on accurate navigation are uniformly overengineered. Not only do they frequently wring more information out of the cues that surround them than we can, or use more exotic or weaker cues than we find conceivable, they usually come equipped with alternative strategies -- a series of backups between which they switch depending on which is providing the most reliable information.

4) A honey bee, for instance, may set off for a goal using its time-compensated sun compass. When a cloud covers the sun, it may change to inferring the sun's position from UV patterns in the sky and opt a minute later for a map-like strategy when it encounters a distinctive landmark. Lastly, it may ignore all of these cues as it gets close enough to its goal to detect the odors or visual cues provided by the flowers. This is not to say that animals do not often rely on approximations and neural shortcuts to simplify these daunting tasks.

5) A third stumbling block has been our presumption that because the earliest cases studied involved "imprinting" (irreversible one-trial learning), animals must have simple navigation programs, which need merely to be calibrated to the local contingencies. This is just what at least some relatively short-lived animals do -- like honey bees for instance, who rarely forage for more than three weeks. But most animals live longer, and in consequence many need to recalibrate themselves.

6) Finally, most researchers deliberately ignored or denigrated the evidence for cognitive processing in navigating animals. This legacy of behaviorism (the school of psychology that denied instinct) puts a ceiling on the maximum level of mental activity subject to legitimate investigation. There are many navigating animals whose behavior lacks any hint of cognitive intervention. However, the obvious abilities of hunting spiders and honey bees to plan novel routes make it equally clear that phylogenetic distance to humans is no sure guide to the sophistication of a species' orientation strategies.(1-3)

References:

1. Able, K.P. and Able, M.A. (1995). Interactions in the flexible orientation system of a migratory bird. Nature 375, 230-232

2. Gould, J.L. (1980). The case for magnetic-field sensitivity in birds and bees. Am. Sci. 68, 256-267

3. Walker, M.M. (1998). On a wing and a vector. J. Theor. Biol. 192, 341-349

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