Animal navigation 1: true navigation and maps Flashcards
What is the definition of True Navigation?
It is goal orientation from an unfamiliar place, over unfamiliar terrain, without direct sensory contact with the goal and without relying solely on path integration.
How does True Navigation differ from using a compass/vector navigation alone?
- A compass provides direction, it tells you which direction to go but doesn’t tell you where you currently are relative to goal. Won;t work if you are displaced
- but True Navigation also requires an internal sense of position (knowing where you are relative to the goal).
- true navigation tells you where you are, so you can know which direction to go even when unfamiliar
What is Path Integration?
- A navigational method where animals continuously update a homeward vector based on their own movements (often seen in ants).
Path Integration vs. True Navigation
- Path Integration relies on self-movement cues (egocentric),
- whereas True Navigation involves knowing your position in a larger spatial context, enabling compensation when displaced.
How do ants respond if they are displaced during foraging?
- when ants are displaced right before they go home (after they have completed summing for home vector)
- They continue following their homeward vector (based on path integration) leading to incorrect destination
- and then search in the wrong spot when they reach where they “think” home should be.
What experiment showed young starlings’ limitations in navigation?
- Displacement experiments found that young starlings on their first migration could not adjust their route when moved,
- they fly in the original direction as if they haven’t been displaced
- indicating reliance on a genetically encoded vector and use of compass
What did adult starlings do differently when displaced to Switzerland?
- Unlike young starlings, when adult starlings displaced they can find their way back home
- They adjusted their trajectory and managed to reach their original overwintering site (e.g., the UK), showing true navigation ability.
Geoffrey Mathews’ Manx Shearwater Experiment
- Shearwaters were displaced thousands of miles away
- They still oriented and returned home quickly.
- This demonstrated strong evidence of true navigation over unfamiliar terrain.
- even there initial orientation was correct and compensated for displacement
How do monarch butterflies navigate differently from birds with true navigation?
- Monarchs have an inbuilt vector orientation for migration but fail to compensate for large-scale displacements, indicating they do not exhibit true navigation.
What navigation strategy do ants primarily use?
Ants use path integration, continuously updating a homeward vector based on their travel distance and direction.
Spiny Lobsters’ True Navigation
- Experiments by Bowles & Lohmann showed lobsters displaced to unfamiliar sites still oriented back to their original capture locations.
- This indicates at least some invertebrates have true navigation capabilities.
What are the key findings from homing pigeon displacement experiments?
- Even if pigeons fail to return home, they often show an initial orientation toward the correct homeward direction (compensated for displacement even initially)
- hinting at an internal “map” system and that they know where they are
What is the Two-Step Navigation Model in birds?
Two step navigation for UNFAMILIAR (familiar also two step but different)
1) Map Step: Determining current position relative to home (internal map).
2) Compass Step: Using directional cues (e.g., sun compass) to find direction and head home
Who introduced the Two-Step Navigation Model?
Kramer introduced the model in 1952, describing a “map” step and a “compass” step for true navigation.
Why is True Navigation considered more complex than simple compass orientation?
- Because it requires an animal to determine its location independently
- then choose the correct direction (compass) to reach a distant goal, even from unfamiliar sites.
What are the main hypotheses for an animal’s “map” in navigation?
- Sun Arc Hypothesis,
- Gradient Map Hypothesis using two cues (e.g., magnetic, olfactory), and
- other potential global cues like infrasound or gravity.
what is a sun arc
- the sun’s altitude and horizontal angle
What does the Sun Arc Hypothesis propose?
- It suggests animals might use the sun’s changing arc across the sky, along with an internal clock, to gauge position (e.g., estimating longitude/latitude),
- but experiments with pigeons have not supported this. experiments show when displaced their orientation uses the time compensated sun compass, and manipulating sun’s horizontal angle artifically didn’t affect orientation
Gradient Map Approach
- gradient map or extrapolated map
- Involves learning the alignment and intensity of environmental gradients (based on cues such as., magnetic, olfactory) in familiar territory first
- Animals then extrapolate these gradients and cues to unfamiliar areas to find home.
How do animals use multiple gradients for navigation?
- By learning at least two independent gradients (e.g., dip angle and intensity in the Earth’s magnetic field, or chemical cues),
- they can form a bicoordinate “map” to determine their position relative to home, forming a vector
- by summing the direction information from the coordinates, they can know where they are relative to their home ven in unfamlliar locations
what are poetntial navigation and environmental cues used for the gradient map?
requires at least 2 environmental cues for bicoordinates
* geomagnetic field gradients
* olfactory gradients
* gravity
* infrasound
* visual
what is the geomagnetic cues in gradient map
- Vigo 1882
- animals might detect variation in earth’s magnetic field
- using 2 cues: the dip angle and total intensity
- these 2 act as bicoordinates and provide 2 different cues which allow animals to infer about its spatial location
- dip angle varies systematically from equator to pole and globally present
- intensity vaires systematically globally too
- However no clear evidence and unlikely to be the case
What evidence challenges the idea of an Earth Magnetic Grid Map for Green Turtles?
- Turtles fitted with magnets swam home from unfamiliar environments just as effectively as controls,
- suggesting magnetic cues alone are not essential for their long-distance navigation (possibly chemical cues are used).
What evidence supprts the magnetic cues for gradient map: Loggerhead Turtle Experiment
- Hatchlings placed in a Helmholtz coil to alter magnetic intensities (52,000 vs. 43,000 nT).
- They reversed swimming direction in response, helping them stay in the favorable currents of the North Atlantic Gyre.
- when they manipulated the magnetic intensities using helmoltz coil, the turtles would always reverse their directions when encoutering 52000nT and 43000nT, indicating they do use magnetic intensities to switch directions
- Unsure if it’s a true “map” or just a signpost system.
How do Spiny Lobsters demonstrate true navigation with magnetic cues?
- When exposed to artificial magnetic fields mimicking unfamiliar locations, the lobsters responded appropraitely follong the magnetic cues as if it was a gradient map
- E.g when induced artifical magnetic fields from north, it induced lobsters to orient south
Do pigeons rely on a magnetic grid map?
- Early studies hinted that magnets disrupted pigeon homing on cloudy days but not sunny days, but replications failed to confirm this.
- Current evidence suggests pigeons likely do not use a magnetic grid map.
Why might wandering albatrosses not use a dip-intensity magnetic grid?
- Around nesting islands, inclination and intensity vary together, giving only one gradient rather than two, hence not forming bicoordinate map and can’t be used effectively
- Experiments with magnets also did not affect their foraging or navigation patterns.
What does “multimodal navigation” imply?
Many species combine multiple cues—magnetic, visual, chemical, infrasound—to navigate effectively over large distances, especially when one cue is unreliable.
Which navigational cues lack clear evidence or have evidence for gradient map hypothesis in many bird species?
- Earths magnetic field: no clear evidence in birds, yet possible in lobsters and turtles
- Sun arc hypothesis: no evidence
- Visual landscape: no enidence
- Infrasound and gravity: no evidence, except recent study showing albatross may be sensitive to infrasound across oceans
- Olfactory hypothesis: Good evidence from Papi 1975
Example in disorientation experiment in pigeons which support olfactory cue as gradient map
- Studies indicate that birds like pigeons can be anosmic (deprived of smell) after being sprayed with anesthesia fail to home properly from unfamilliar sites
- suggesting smell-based gradient maps may exist.
what were some problems with this disorientation experiment on olfactory cues?
- non-specific effects of the anesthesia (such as loss of motivation or interference with the magnetic sense) could theoretically cause disorientation,
- However, subsequent experiments in familiar areas showed that anesthetized birds could orient properly when relying on learned landmarks – supporting that they can orient using other navigation methods, linking disabled olfactory system to true navigation in unfamilliar environments
why are disorientation experiments less robust that re-orientation experiments
- disorientation experiment is less robust than an reorientation experiment because reorientation experiment allows predictable manipulation of the cue (reduces non-specific effects),
- instead of just abolishing it in disorientation experiments (more potential non-specific effects)
what is the reorientation experiment that also supports olfactory cues used for true navigation
- false site release experiment
- birds were exposed to the smell at a false site which would orient them south
- they were released at an unfamiliar real release site where they smelled filtered air with no olfactory cues
- they orient southwards as if they were released from false site and orient southwards, when in fact they should orient north from real site to home
what is the comparative study showing use of magnetic and olfactory cues in birds for true navigation
- manx shearwater
- one group was anosmic, and one group had magnets attached to heads to disrupt magnetic cues, one group was control
- all equipped w GPS
- contral and magnetically manipulated birds were able to direct homing trajectories
- anosmic birds showed significant disorientation, slower progress home, and inconsistent orientations
- suggests that in manx shearwater they rely on olfactory cues, and magnetic cues are not significant
What are some key “take-home” points about True Navigation?
- True Navigation requires 2 step processL an internal map plus a compass.
- Displacement experiments confirm some species (birds and lobsters) can compensate for being moved to unfamiliar places, whereas other invertebrates dont show true navigation
- The exact nature of the “map” varies by species and may involve multiple cues.
integration of 2 step true navigation process
- step 1: map component: map cues (mostly olfactory) determine where they are relative to the target in unfamiliar environments
- step 2: compass component: after determining where they are, animals use compass (often time compensated sun compass or magnetic compass) to establish direction for homeward travel
what do birds have to learn in order for true navigation?
- for the map component to work, birds must learn the pattern of envrionmental cue gradients around home
- then extrapolate this pattern to unfamiliar environments
Disorientation Experiments Using Olfactory Disruption
- Pigeons’ nasal mucosa was sprayed with anesthetic to block smell.
- These birds became disoriented at unfamiliar release sites.
- Control birds oriented correctly, implying smell is vital for their map step.
How do we rule out non-specific effects in olfactory disruption experiments?
By showing that anesthetized pigeons still orient well in familiar areas (using landmarks), confirming the disorientation in unfamiliar sites is tied to the loss of smell rather than general impairment.
How do reorientation experiments strengthen the case for olfactory navigation?
By predictably manipulating odors (rather than just removing them), researchers can show that pigeons follow the false olfactory cues, ruling out alternative explanations like lack of motivation.
What did Corrie’s Shearwaters experiment reveal about magnetic vs. olfactory navigation?
Birds with magnets still homed effectively, but anosmic birds showed disorientation and slower homing, indicating olfactory cues are critical while magnetic cues are less important for these seabirds.
Why do anosmic shearwaters take longer to find their way home?
Without smell, they lack essential map information, leading to poor initial orientation and slower progress, despite eventually finding home after several days.
Integrating the Two-Step Process in True Navigation
- Step 1 (Map): Determine position relative to home (often via olfaction in birds, magnetic cues in turtles/lobsters).
- Step 2 (Compass): Use a directional reference (e.g., time-compensated sun compass) to travel home.
How do clock-shift experiments confirm the compass step in navigation?
By altering birds’ internal clocks, their sun compass reading is shifted, causing predictable deviations in flight direction, thus confirming a time-compensated compass.
Why might lobsters and loggerhead turtles rely more on magnetic cues than birds?
Their life history (e.g., open-ocean or seafloor migration) may make local odors less reliable, while Earth’s magnetic gradients remain more consistent over large areas.
How do detailed local/familiar maps reduce reliance on long-distance navigation cues?
As animals learn familiar landmarks and local cues, they no longer need to rely solely on global gradients or olfactory maps for orientation within their home range, instead relying on landmarks and visual cues
What are the key findings about olfactory navigation across species?
- Birds like pigeons and shearwaters strongly depend on olfaction in unfamiliar areas.
- Magnetic cues are important for some turtles and invertebrates.
What is the main conclusion of these experiments on True Navigation?
True Navigation requires both a map (positional sense) and a compass, and for many bird species, olfactory cues play a dominant role in determining where they are before orienting home.
