Bird Navigation Tony Ludlow tony ludlowmodelresearch com www

Bird Navigation Tony Ludlow tony. ludlow@modelresearch. com www. modelresearch. com 12 th Jan 2006

Aims of lecture • Show what birds achieve • Discuss views about how they do it • Illustrate the way various systems interact and how birds calibrate one system from another • Review mistakes in the progress of research

Types of navigation • Piloting • Compass sense • True navigation

Piloting • Difficult to rule out, given height at which birds fly • Not possible for Bronze-winged cuckoos • Other methods can be demonstrated

Compass v true navigation • Perdeck’s experiments • Tracking birds

Perdeck (1958)

Michener and Wallcott's pigeon harness

Combination of methods Michener and Wallcott (1967) tracked single pigeons and found 1. A phase of straight flight, not usually towards home: compass sense 2. Flight heading accurately towards home: true navigation 3. Use of landmarks within 10 miles of loft.

Michener and Wallcott (1967) tracks

Sensory cues: problems in research • Circular statistics • Redundancy not understood (Pennycuick, Matthews) • Vanishing direction • Piloting cues not eliminated

Kramer (1957) • • • Starlings --- day migrants Circular cage – recorded from each perch Birds showed migratory direction Confused by overcast Adjusted for sun movement (90 degrees in 6 hr)

Sun compass: Kramer (1957)

Kramer (1957) a) Compensated for normal sun movement b) Followed sun when it was shifted by mirrors (so not magnetism, etc. ) c) 6 hr clock shift caused 90 deg shift d) `Sun’ kept stationary; birds changed their angle to it.

Stellar compass • Sauer and Sauer (1955) showed blackcaps chose correct autumn directions under a planetarium and reversed direction in spring • Emlen (1970) showed that indigo buntings respond to celestial rotation; they were taught to use other constellations as `north’ star • Bellrose (1967) used radar to show that migrants were well oriented at night, even in overcast • May be they see glimpses and keep straight using the direction of wind gusts (Nisbett, 1955)

Magnetic compass • Rejected in 1960 s • Evidence in bees (eg. Lindauer and Martin, 1972) • Keeton (1971) showed magnets confused pigeons under overcast (could act on compass or true navigation) • Wiltschko and Wiltshcko (1972) showed that robins responded to the angle of dip if strength of field similar to earth's • Wallcott and Green used electric coils on pigeons. NUP disoriented, SUP did not.

Polarised light • Brines (1980) demonstrated that rotation of polarised light was used during day • Seems to be this rather than the sun which is used • Birds use rotation of stars to find north • Using rotation, they don’t need a clock

True navigation • Perdeck's adult starlings showed true navigation • So did Michener and Wallcott's tracks • The vanishing direction is easy to measure but very often wrong.

Theories of true navigation • Every twist and turn is integrated (spider, millipedes, Walraff (2000)) • Celestial cues could be used to find home direction (Board of longitude prize) • Magnetic variation across earth's surface • Odours

Celestial navigation? • Requires astonishing accuracy of time sense • Requires astonishing accuracy of visual discrimination (frosted glass contact lenses) • Keeton showed that pigeons home when they cannot see the sun • After a time shift, pigeons show compass errors not errors in home direction.

A magnetic map? • Pattern of magnetism over earth's surface could be used in principle • Wiltschko and Wiltschko (1996) showed this would require minute discrimination: 0. 03%. Daily variations are of same order. • It is not clear how the map would work: Angle of dip; Boles & Lohmann (2003) lobsters

Home direction from odours Wallraff (1967) reared pigeons in screened lofts: • Those which could see the sun but not feel the wind got lost • Those which felt the wind but never saw the sun were fine • Odour hypothesis From 1972 Papi and colleagues did many experiments on anosmic pigeons • There is a debate in the Navigation symposium. See Wallraff (1996); Wiltschko (1996) and Able (1996) • Odetti et al (2003) effects of flight experience on orientation performance

Calibrating the systems • Birds are not born with a star map • Magnetic compass (angle of dip) reverses at the equator, so needs to be recalibrated • Savannah sparrows are born with a response to magnetic field • Helbig (1996) Genetics of response • Migratory song birds also respond to celestial rotation • Celestial compass updates the magnetic one during migration • But Sandberg et al (2000), 4 species calibrate star map with magnetic cues.

Redundancy and balance between systems • • Keeton: sun or magnets Multiple systems How much weight does a bird put on each Learning two cues could mean less weight to each • Individuals may differ, based on their experience. That would make experiments hard to interpret