Migration and navigation 1 Flashcards
Why do animals need to navigate?
Local movements within familiar area
Local spatial responses to unfavourable conditions
Dispersal to new habitat
Regular, predictable movements to new areas; usually long-distance relative to home range (migration?)
Homing: return to a locality after intended movement or unintended movement (displacement / translocation)
Key definitions
Capacity to move: drift, muscle-powered locomotion, selective tidal stream transport
Directional cues:
-Orientation: is maintenance of the body position/alignment relative to an external cue
- Piloting: use of local landmarks and spatial memory to reach a site (goal)
- Navigation: ability to head towards and locate goal in unfamiliar territory, after moving in anew and unfamiliar direction
Simple orientation cues
Many animals show simple orientation responses that are fundamental to them remaining in or locating appropriate conditions
Kinesis – animal’s response proportional to intensity of stimulation
Orthokinesis – Increased stimulation results in increased speed of locomotion
Klinokinesis – Rate of direction changing increases as stimulus increases
Taxis – movement towards or away from stimulus– more useful for directed movements, and potentially used for finding suitable areas
Taxis
Example: Water Boatmen are positively phototaxic when they need air and negatively phototaxic once air is replenished
Many river fish are positively rheotactic – align and swim against the flow. This helps to retain position against current, but is also important for directing upriver migration, e.g. by adult salmon
Orientation mechanisms
Local movements and migrations may use an integration of appropriate orientation mechanisms
e.g. Orientation mechanisms demonstrated to occur in different life cycle stages of Oncorhynchus Pacific salmon
(see notes for diagram)
Is large-scale motor performance necessary for long-distance migration?
Not necessarily, it may be passive movement – Long distance migrations may be achieved by passive drift, with sensory capability and local orientation, especially ‘on arrival’
Example:
Migration of European and American eel leptocephali larvae achieved mostly passively on the Gulf Stream currents
Orientation and navigation cues
Landmarks
Celestial cues
Electromagnetic fields
Chemical cues
Landmarks
Heliconias butterfly return to the same roosts each night
Dragonflies hawk for prey and return to a number of selected resting sites
Rockpool fishes able to find their way around pool and relocate it based on rock positions etc.
Retinotopic cues - Many animals are adept at piloting
Animal moves until the viewed image of a landmark falls on the same retinal locations memorized during a previous visits.
Short distances: Digger wasps circle the nest surveying the nest entrance in relation to local landmarks. Tinbergen removed pine cones placed around digger wasp nest and noticed that they then found it hard to find the nest entrance.
Longer distances: Landmarks for example, wood ants use retinotopic learning over long distances; they memorize & walk parallel to a distant edge. When the wall’s height was changed, the ants’ paths consistently shifted toward a lowered wall and away from a raised wall.
Celestial cues
Sun and moon (and other stars)
Used by wide variety of animals; relative position of sun (or moon / star map), in some cases also direction of polarised light (still works in cloudy weather)
Many tests based on homing and displacement
e.g.Arthur Hasler’s experiments on homing by displaced white bass in Lake Mendota, USA showed strong homing to breeding site after experimental displacement when sunny, poor when cloudy.
Celestial cues: Sun compass: orientation in White Bass
White bass homed using sun compass orientation (with time correction), but orientation poorer when cloudy
Sun rises predictably in east, is at its azimuth at noon, sets in west
Body clock enables animals to take account of position and adjust bearing relative to sun
Note: orientation is not highly accurate, but is enough – piloting can then take over
Celestial cues: Sun compass: bee waggle dance
Karl von Frisch (1886-1982) showed bees can adjust their flight using a sun compass;
Bees are able to perfectly orientate with <1% of blue sky;
They use UV light -although it is dim, it is resistant to interference.
Number of waggles important for distance
Shape of dance important for altitude
Celestial cues: star compass: many bird species
Many birds migrate at night
Emlen worked on indigo buntings (migrate N in spring, S in autumn) and stellar orientation.
Designed Emlen funnel to measure migratory restlessness directionality at dusk
Celestial cues: Star compass: Dung beetles
Dung beetles use stellar orientation, especially light from the milky way, to orientate and roll their dung balls back to their burrows.
Equally able on moonless nights.
Lose orientation ability on cloudy nights.
Electromagnetic fields: geomagnetic cues
Major cue for large-scale spatial movements, especially important for long-distance navigation.
Flowing metal (esp. Fe) in Earth’s core creates electric currents –Earth’s rotation generates magnetic field
3 main potential magnetic cues :
1) Polarity –S to N (currently)
2) Angle of inclination (dip) of magnetic field lines –steeper near poles
3)Intensity of field –strongest at poles
Response to alteration of geomagnetic field demonstrated in many inverts & verts
Electromagnetic fields: build your own compass
Biogenic magnetite & maghemite (biologically secreted iron crystals - widely found in animals + some bacteria) – research by Kirschvink, Diebel etc on wide range of taxa. In specialised cells which link directly to nerve endings (= trigeminal nerves in vertebrates) passing to brain.
The brain builds a magnetic map used in subsequent navigation
