and NaviRO

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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 anddocumented their migration through354 recaptures.

Adults move NW from releasesite 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 programtermed Vector Navigation

Blotting PaperFunnel

Orientation Cage – for quantifying the intensity and direction of Migratory Restlessness

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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

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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 byGustav Kramer in 1951 working withstarlings in orientation chambers.

To use a sun compass birds must be able to compensate for the changingposition of the sun – time compensation.It turns out the sun compass is tied to abird’s circadian clock and if their clock isreadjusted 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 azimuthdirection.

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 nightwhen 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 planetariumwith 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 constellationsto 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 positionsinstead they would not

When Emlen used Betelgeuseas 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 ormanipulated 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 tovary the magnetic field of the birds in cages and birds predictablyVary 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 dippoints N dips N NE NE

points S dips S SW SW

points S dips N SW NE

points N dips S NE SW

points N none NE random

Unnaturaloccurrence

SouthernHemisphere

Prediction if using:

“N” = compass directionN = true direction

• The magnetic compass seems to develop spontaneously in juvenile birds ifthey 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: