Birds (Lecture 9) Flashcards
Orientation vs navigation
Orientation: ability to identify compass directions and acquire an internal representation of them
Navigation: ability to identify current position and move to a new one (knowing where you are and where you want to go)
Navigation/Orientation cues (X6)
Geomagnetic cues, olfactory cues (i.e. gradients), sun position, star positions, local landmarks, polarized sky light
Difficult to research because animals are likely to use multiple strategies
Premigratory restlessness and the cues birds use/how they have been shown
Key research tool. Measured with Emlen’s Funnel. Key experiments by Merkel, Wiltschko and Fromme with robin.
Robins generally orient in appropriate migratory direction, even without external visual cues - must be able to sense compass directions.
Use MAGNETIC FIELDS: Bird on ink pad, blotting paper on sides, number of marks counted, in spring –> N, in autumn –> S, no magnetic field –> random. Both direction and angle (further from earth = more angular) of magnetic field of the earth is used. Vectors are calculated to locate themselves within the magnetic field.
Use the position of the SUN: Always tries to go in opposite direction to sun i.e. same direction as the sunlight travels (mirrors used to change apparent position of sun).
Use the position of the STARS: sky rotates around Polaris, birds use the patterns of rotation. Has been tested in planetariums.
Cochran et al (night migrants)
Used 2 types of thrush (night migrants) to research how they determine the direction of flight - gray-cheeked and swainson
Manipulated magnetic field at twilight, before release. Tracked their flight paths. Started off in wrong direction.
Found they use combination of sun position and magnetic field. At twilight, use cues to calibrate compass (position of setting sun in relation to magnetic field). Recalibrate next night to alter direction –> corrected.
Do birds have magnetic receptor? (X3 theories)
Ferromagnetic (iron, cobalt, nickel - strongly attracted by mag. field)
Paramagnetic (aluminium, platinum - weakly attracted)
Diamagnetic (copper, silver - repelled)
Most evidence for the first: All minerals containing iron are attracted by magnets. When there are magnetic domains, magnetic moments align (and when unmagnetized, they don’t align). Magnetite exists naturally (Fe3O4), which has been shown to align with Earth’s magnetic field. Has been shown to exist in animals including salmon and chiton (mollusc) and bacteria.
Could be attached to mechanically gated ion channel.
Behavioural test for magnetoreception
Pigeons (Mora et al): contained within apparatus, food appears at either end. Trained to collect food based on magnetic field alone.
Where is the magnetoreceptor (X3 ideas)
Same experiment with pigeon trained to collect food (mora et al): put magnet on the cere of the pigeon (protrusion on the beak). Couldn’t complete task - blocked magnetoreception. Magnetoreceptor could be in the beak? (Also blocked if ophthalmic branch of trigeminal nerve cut - must be located somewhere connected via this?)
Other experiment (Fleissner et al) showed chains of magnetite exist in pigeon’s beak, localised to particular points.
Other experiment applied magnetic field to this area and recorded increase in response of trigeminal ganglion.
Not straightforward - Treiber et al disproved: found that magnetite-containing cells in the beak are macrophages rather than neurons and that they’re distributed throughout the beak.
Wiltschko showed robins can’t orient to geomagnetic cues when right eye covered - sense must be in right eye?
Wu & Dickman suggest magnereceptor also in inner ear. Used pigeons and c-fos (marker for cellular metabolism). Magnetic pulse induced c-fos in vestibular nuclei. Reduced by lesioning inner ear (lagena). Also found cells in VN that were responsive and unresponsive to magnetic stimuli - can code direction and intensity of magnetic field (have direction preference). They suggest that ions channels in the otolithic membrane respond to tension of the membrane. Magnetite crystals in the membrane are twisted by external magnetic forces, which alters the tension.
Olfaction for navigation (2 studies)
Study showed impairing olfaction (by bilateral sectioning of olfactory nerve) in birds impairs their navigation. Used inexperienced homing pigeons, released from 4 different sites. Controls could almost always fly home, anosmic birds never returned home.
Also showed that impairment was more apparent with more distant release sites.
Similar study showed that pigeons oriented towards home upon release. BUT filtered air –> no preferred direction.
Pigeons use landmarks
Lipp et al: used GPS-tracked pigeons released from various locations. Release from NW –> most followed roads/railways rather than direct beeline. Often used the road junctions even if it added distance to their journey. Size of road partly influences following.
Seemed that local area had “traffic nodes” where pigeons would be seen circling to make decisions of direction - seem to serve as beacons, which the pigeons hop between.
Routes shifted with experience - follow roads more (more reliable method).
Why follow man-made landmarks? (X3)
- Avoid the unknown?
- Familiarity could reinforce road-following?
- Free up brain resources (easier than using compass directions)?
Evidence for continental map in birds
Study using white crowned sparrows. Captured birds just before they migrated and moved then from the West side of the USA to the East. Birds that had migrated before compensated, whereas juveniles who had never migrated did not.
