and Navi R O E I N AT T O I N gation

Orientation: The state of knowing your location Navigation: The state of knowing how to move from your present location to a specified destination Its useful to consider an inexperienced individual migrating for the first time, and doesn’t migrate with more experienced adults w/whom they might learn from

In the 1950s Perdeck banded and translocated 10,000 starling from The Netherlands to Switzerland and documented their migration through 354 recaptures. Adults move NW from release site toward the correct over- wintering site Juveniles (first-time migrants) moved SW the correct direction if traveling from the captured site These results demonstrate that adults shown true navigation (they “home”), whereas Juveniles execute a migratory program termed Vector Navigation

Blotting Paper Funnel Orientation Cage – for quantifying the intensity and direction of Migratory Restlessness N S WE

Garden Warbler - Warbler held at constant 12:12 light regime - Not exposed to the night sky, but exposed to the Earth’s normal magnetic field

** * But adult birds possess truly amazing homing abilities – how do they do it??

Consider one of the following mechanisms: (1)Maintain direct sensory contact with the site (see, hear, smell your goal) (2)Use some sort of random or patterned search in an attempt to encounter something familiar (3) Inertial Navigation – your return trip is the opposite of route of the way out; log turns, distances, etc. (4) Use a learned mental map to localize your position relying on familiar landmarks (5) Possess a mental map based not on familiar landmarks but of extensive gradients that act as analogs of latitude and longitude

Wallraff (1980) – transported pigeons under tightly controlled conditions to prevent them from perceiving any navigational info: Airtight cylinders with bottled air Light turned on and off at random Loud white noise played Cylinders enclosed in magnetic coils that provided a randomly changing field Placed on a tilting turntable hooked to a computer that varied tilt and rotation randomly Pigeons made it back – True Navigation Currently almost all research is focused on the map and compass model of navigation. Homing is a two-step process involving a mechanism to identify a spatial position (map) and another to identify directions (compass). Sun Star Magnetic Polarized light

Sun Compass – first discovered by Gustav Kramer in 1951 working with starlings in orientation chambers. To use a sun compass birds must be able to compensate for the changing position of the sun – time compensation. It turns out the sun compass is tied to a bird’s circadian clock and if their clock is readjusted they make predictable mistakes

These experiments have been done many times and indicate some peculiarities: When a clock is shifted in a certain way, they mistake a noon sun for sunrise!! Animals ignore differences in the sun’s elevation, but consider only its azimuth direction. The sun is also the first choice in homing pigeons. Finally, to use as a compass, pigeons must learn the sun’s path (i.e., rises in the E, sets in the W). They may use a magnetic compass to assign directions to the sun’s azimuth

A sun compass is obviously ineffective at night when many birds migrate. Star Compass – first discovered by Sauer (1957) who believed birds were born with a genetically encoded stellar map Steve Emlen later working in a planetarium with indigo buntings in orientation cages showed this was not true. Instead, young buntings observe the rotation of the night sky (Earth's rotation) and learn the center of the axis of celestial rotation – Polaris – North Star Emlen exposing birds to normal and manipulated skies and changing the Axis (rotate around Betelgeuse) 

Apparently birds memorize the position of the stars in the circumpolar constellations to select the proper direction The figure shows that when birds are exposed to the night sky offset from the true time of night they still migrate the proper direction – if they used the rotational positions instead they would not

When Emlen used Betelgeuse as the polestar, birds migrated the correct directions when tested under a normal night sky in fall migration All birds grew up w/o see a point source of light Groups b and c where exposed every other night to normal or manipulated night sky for two mos.

Magnetic Compass – first discovered by Merkel and Wilschko in the 60s by putting birds in orientation cages w/o sun, light, or star cues. Helmholtz coils – were used to vary the magnetic field of the birds in cages and birds predictably Vary there pattern of migratory restlessness At least 18 spp of birds, including homing pigeons have shown magnetic orientation

Unlike our compasses however, birds do not sense magnetic polarity but rather sense the Earth’s magnetic field. We don’t know how (SEE NEXT SLIDE). At the poles the magnetic field is strongest and intersects the Earth perpendicular At the equator the magnetic field is weakest and magnetic field lines intersects the Earth at 0 degrees

Field Dip N/S dip points N dips NNENE points S dips S SWSW points S dips NSW NE points N dips S NESW points N noneNErandom Unnatural occurrence Southern Hemisphere Prediction if using: “N” = compass direction N = true direction

The magnetic compass seems to develop spontaneously in juvenile birds if they grow up in the proper magnetic field. It appears to serve as the back-up compass for many migrants when the sun is not visible And it serves to assign directions to the sun’s azimuth (i.e., provides the standard reference compass)

Compasses (and probably maps) are redundant Their use is flexible based upon info available, but there would appear to be a hierarchy of use For instance, many birds appear to rely on the magnetic compass, but not pigeons, which prefer the sun and use it to over-ride information based on the former when the sun is exposed Compasses also act to (re)set each other in ways that we don’t understand We also do not understand navigation to migratory destinations: is it mostly vector navigation til the bird recognizes (odor, magnetic field, visual cues?) its destination? We do not have the answers. A few summarizing generalizations: