[Paleopsych] SW: On Animal Navigation

Premise Checker checker at panix.com
Tue Oct 11 23:56:48 UTC 2005

Animal Behavior: On Animal Navigation

    The following points are made by James L. Gould (Current Biology 2005
    1) Juvenile birds regularly migrate thousands of kilometers. Most fly
    at night, without their parents to guide them. The mystery of how
    birds manage this apparent impossibility inspires ever-more-heroic
    attempts to defeat them at this crucial task. New work [1] reports a
    dramatic new way to confound south-bound sparrows: take them along or
    above the Arctic Circle aboard an icebreaker; fly them to experimental
    sites by helicopter; and see what directions they choose. Only time
    will tell whether, once again, the birds have another layer of
    yet-to-be-deciphered finesse in their navigation repertoire, or if
    they finally have been driven to the computational wall and are
    responding in a consistent "does-not-compute" manner.
    2) Exactly what does a migrating species require? First, the birds
    need a compass to know which direction they are going, and they come
    supplied with several: the earth's magnetic field (indicating magnetic
    north); the celestial pole (indicating true north, about which the
    stars appear to rotate at night); and the Sun's location (as inferred
    from patterns of sun-centered polarization which, with a suitable time
    sense, also specifies true north). Second, they need to know at least
    roughly -- and in some instances quite precisely -- where they are
    relative to their goal. In the case of homing pigeons, this ability is
    known as a map sense, and has a resolution of a very few kilometers
    3) The map sounds quite mysterious compared to the compass, but they
    are both daunting challenges. Consider the problem from the bird's
    point of view. First of all, it is cloudy a lot, so much of the time
    you can forget about using celestial cues. But then, why not just use
    magnetic north? If you are born at a high latitude -- where large
    numbers of species breed -- there is often a large discrepancy between
    magnetic and true north -- the declination error, which arises in part
    from the 1400 kilometer separation of this point from the geographic
    pole. Worse, declination generally changes as you fly south. And even
    if the evening is clear, the stars and patterns of polarized light
    change with both latitude and date.
    4) Birds dispose of these problems by periodically calibrating one
    compass against the other [3;4]. Recent evidence has shown that when
    the sky is clear, the recalibration occurs daily, and takes only about
    an hour [5]. The accuracy and sensitivity of this system is
    astonishing: in tests performed near the conventional north magnetic
    pole -- where the earth's field lines plunge vertically into the
    planet, providing no directional information at all -- birds are well
    oriented just a few dozen kilometers away, where there is only a 1.1
    deg deviation from vertical. (There is another "pole", one of magnetic
    intensity, located about 2000 kilometers farther south near the
    western edge of Hudson's Bay, which is critically important in
    magnetic-map theories.)
    5) But how do the birds know which way to fly in the first place. Most
    species have an innate starting direction: put them as juveniles or
    adults in a cage during migration season, and they will all try to
    escape in roughly the direction they ought to fly to get to their
    wintering grounds. But there is a danger here in assuming that the
    birds know only as much as their behavior suggests: some species
    display accurate departure directions in cages, while others select a
    consistent but quite incorrect one (west into the sunset). But release
    the same "misguided" birds with tracking beacons, and they set off in
    the direction they ought to have chosen in the cage. The results of
    Åkesson et al. [1] take on more meaning in this light. They found that
    sparrows moved gradually east above the Arctic Circle completely
    altered their migration strategy after encountering the massive
    natural change in declination near the magnetic pole.
    References (abridged):
    1. Åkesson, S., Morin, J., Muheim, R., and Ottosson, U. (2005).
    Dramatic orientation shift of White-crowned Sparrows displaced across
    longitudes in the high arctic. Curr. Biol. 15:1591
    2. Gould, J.L. (1980). The case for magnetic sensitivity in birds and
    bees (such as it is). Am. Sci. 68, 256-267
    3. Able, K.P. and Able, M.A. (1990). Calibration of the magnetic
    compass of a migratory bird by celestial rotation. Nature 347, 378-380
    4. Able, K.P. and Able, M.A. (1995). Interactions in the flexible
    orientation system of a migratory bird. Nature 375, 230-232
    5. Åkesson, S., Morin, J., Muheim, R., and Ottosson, U. (2002). Avian
    orientation: effects of cue-conflict experiments with young migratory
    songbirds in the high Arctic. Anim. Behav. 64, 469-475
    Current Biology http://www.current-biology.com
    Related Material:
    The following points are made by W.W. Cochran et al (Science 2004
    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
    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
    4. D. C. Outlaw, et al., Auk 120, 299 (2003)
    5. W. L. Engels, Biol. Bull. 123, 94 (1962)
    Science http://www.sciencemag.org
    Related Material:
    The following points are made by James L. Gould (Current Biology 2004
    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
    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
    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)
    Able, K.P. and Able, M.A. (1995). Interactions in the flexible
    orientation system of a migratory bird. Nature 375, 230-232
    Gould, J.L. (1980). The case for magnetic-field sensitivity in birds
    and bees. Am. Sci. 68, 256-267
    Walker, M.M. (1998). On a wing and a vector. J. Theor. Biol. 192,
    Current Biology http://www.current-biology.com

More information about the paleopsych mailing list