Navigation and Migration Finding One’s Way About
Focus on the Hippocampus• The hippocampus is a part of the forebrain, located in the medial temporal lobe. It belongs to the limbic system and plays major roles in short-term memory and spatial navigation (see Alcock, Chapter 4, pages 130-133).• Humans and other mammals have two hippocampi, one in each side (hemisphere) of the brain. In rodents, where it has been studied most extensively, the hippocampus is shaped something like a banana. In humans it has a curved and convoluted shape that reminded early anatomists of a seahorse. The name, in fact, derives from the Greek word for seahorse (hippos [horse] + kampos [sea monster]).
Hippocampus (Cont’d)• The results of a large number of studies on the vertebrate hippocampus suggest that this area of the brain is linked to the ability of the individual to utilize spatial information.• Neurobiological studies indicate that specific areas or cells of the organ provide very specific information about the location of an individual.• Lesion studies reveal that damage to the hippocampus results in impaired spatial ability.
Hippocampus (Cont’d)• Information collected via electrodes from individual cells within the hippocampus of free-moving rats has revealed a class of cells now called “place cells.”• Experimenters have discovered the each of these cells is sporadically active as the rat navigates its environment.• However the cells’ activity is far from random: each cell fires maximally when the rat reaches a particular location.• The cells don’t appear to respond to location in space, but to particular landmarks, or combinations of landmarks that have a particular spatial relationship to the current position of the animal.
Hippocampus (Cont’d)• In Alzheimer’s disease the hippocampus is one of the first regions of the brain to suffer damage; memory problems and disorientation appear among the first symptoms.
Enlarged Hippocampi (Alcock, p. 131-132• Prediction: human brains, as well as those of food-storing birds, should possess and enlarged hippocampus that give them the spatial memory needed to survive.• London taxi drivers: the average posterior hippocampal size was larger than in a comparable group of non-taxi-driving men. The more years of taxi driving (the more navigational experience), the larger the posterior hippocampus.
The Hippocampal Complex in Food-Storing Birds (D.F. Sherry, A.L. Vaccarino, K.Buckenham, R. Her, 1989)• Three families of North American passerines - chickadees, nuthatches and jays - store food. Previous research has shown that memory for the spatial locations of caches is the principal mechanism of cache recovery.• It has also been shown that the hippocampal complex (hippocampus and area parahippocampalis) plays an important role in memory for cache sites.• The hippocampal complex is larger in food-storing birds than in non-food-storing birds. This difference is greater than expected.• Natural selection has led to a larger hippocampal complex in birds that rely on memory to recover spatially dispersed food caches.
Enlarged Hippocampus• European marsh tits (Parus palustris) are avid food hoarding birds that might store 50-100 seeds in a single morning. These birds can remember where a food item was hidden, what kind of food it was, and whether or not the cache has been used.• The closely related blue tit (P. caeruleus) does not hoard food and so presumably does not have the same spatial memory needs (tits are related to chickadees & titmice).• Juvenile marsh tits and blue tits have similar hippocampal volumes (as neither stored seeds), but adult marsh tits have much greater volumes—indicating that hippocampal enlargement does not happen util the birds begin to experience food-storing behavior.
Hippocampal Injury Disrupts Navigation• Rats subjected to hippocampal damage lose the ability to solve mazes.• Homing pigeons subjected to such damage also have disrupted spatial ability.---Lesioned pigeons released 30+ km from their home loft were unable to home even if they were familiar with the release site;---but the pigeons did set off in the right direction, so the hippocampus doesn’t seem to be involved in their compass sense.---Such results suggest that the hippocampus is involved in both the acquisition, storage and retrieval of spatial information.
digger wasp Navigation• Navigation: the science of getting…from place to place; esp: the method of determining position, course, and distance traveled. (Merriam-Webster, 1987)• Niko Tinbergen’s classic experiment involving the digger wasp:---the female wasp is able to return directly to her tiny nest burrow in the ground after a provisioning flight because she first memorizes the relative positions of landmark objects;---NT surrounded a wasp nest burrow with pine cones; then, after the wasp had emerged from the entrance and flown away, he moved the ring of cones a short distance away so that the entrance now was outside the ring.
Digger Wasp Experiment (Cont’d)---The returning wasp flew directlyto the center of the cone ring, not tothe entrance of the burrow only afew feet away.---She searched in vain for theopening in the middle of the ring.
Digger Wasp Experiment (Cont’d)• Wasps of the genus Sphex (commonly known as digger wasps) are predators that sting and paralyze prey insects. There are over 130 known digger wasp species.• In preparation for egg laying they construct a protected "nest" (some species dig nests in the ground, while others use pre-existing holes) and then stock it with captured insects.• Typically the prey are left alive, but paralyzed by wasp toxins. The wasps lay their eggs in the provisioned nest. When the wasp larvae hatch, they feed on the paralyzed insects.
Trail Laying• Trail laying and trail following as a navigational method are common throughout the animal kingdom.• Ants use pheromone trails as a method by which many foragers can efficiently exploit a new food source.• When it finds a food source too large to exploit alone, a foraging ant returns quickly, and by a very direct route to its nest; as it does so it deposits a pheromone trail on the ground behind it.• At the nest the returning individual performs stereotype behaviors designed to recruit others to the food source.
Ants Trail Laying• By following the pheromone trail these recruits are able to go directly to the food source, and, as each of them returns, they too deposit pheromones and the trail is reinforced.• As the food source is exhausted the ants will stop returning and no trail reinforcement will take place; the trail quickly disappears so no ants waste time following it to no reward.
Dead Reckoning• Dead reckoning. 1: the determination without the aid of celestial observations of the position of a ship or aircraft from the record of the courses sailed or flown, the distance made, and the known or estimated drift. 2: GUESSWORK (Merriam Webster, 1987).• Dead reckoning. A corruption of the term “deduced reckoning” and refers to an individual’s ability to deduce its current position in relation to another location by taking into account the direction(s) and the distance that it has traveled between the two (G. Scott, 2005).
Deduced Direction & Distance• Ants, in common with a number of other species, rely upon external cues to guide them to their ultimate destination.• Desert ants appear to use global environmental cues rather than local landmarks by which to navigate—they use the sun, or more precisely, the angle between the direction of movement and the position of the sun relative to the horizontal plane; they take into account the movement of the sun across the sky as the day progresses (a kind of built-in computer system).
Japanese Wood Ants• Japanese wood ants, on the other hand, use visual landmarks in preference to chemical trails or celestial cues.• Researchers, employing various kinds of visual barriers blocking landmarks, have demonstrated that Japanese wood ants use features of the skyline (prominent tree tops, for example) as navigational guides.• The ants in the experiments wandered until they could reach a position whereby they could see once again the cueing landmarks.
Ant Visual Landmarks• Ants will regularly stop, turn, and stare at a prominent landmark feature as they move away from it during a foraging trip.• It is thought that during these “learning walks” the ants commit to memory key objects in their visual field; on subsequent trips they can compare these snapshot memories with actual views.• In this way they are able to deduce information about the distance and direction of their goal.
Japanese Ant Path Directions: With and Without Obstructions X = release point N = nest• X------------------------------------------- N• X-----------------------<E [obstr. on ground]• X------<E [obstr. just off ground]E>--N E------4. X--<E--------E>[obstr. higher----------N E------/ off ground]
Cognitive Maps• The ability of an animal to define various locations within its environment and then integrate this information is the basis of a cognitive map.• Cognitive maps enable animals to plot routes through their surroundings based upon information they have stored in the mental map.
Rat Cognitive Map (R. Morris’ Experiment)• Rats can be trained to swim through opaque water to the safety of a platform that is invisible to them because its surface is just a fraction below water level.• When a rat is introduced to the water at a novel location, but the platform is in the same location, it swims directly to the platform--it has used its cognitive map to deduce where the platform is still located.• When the platform is relocated, however, the rat carries out an exhaustive, wandering search of the area where it expected to find the platform, before swimming elsewhere and actually finding it.
Homing and Racing Pigeons• Homing and racing pigeons are regularly taken by their owners to release sites hundreds of miles from their home lofts, and, and, amazingly, the vast majority of the birds are able to quickly return home without any prior experience of the journey they undertake (see Alcock, Chapter 4, pages 133-134, esp. Fig. 4.40).• To do this they need to determine their current position and their position relative to home (an internal map sense).• Next they need to know in which direction to fly and how far to fly; for this they need an internal compass sense and a means of measuring distance.
Homing & Racing Pigeons (Cont’d)• Evidence points to the fact that the position of the sun is used by pigeons as a compass.• The birds relate the position of the sun in the sky to their internal body clock and find the compass bearing that takes them home.• On cloudy days or at night pigeons are able to use a magnetic sense by which to orient.• Attaching a magnet to a pigeon on a cloudy day is sufficient to disrupt its homing ability (but not on a sunny day).
Homing & Racing Pigeons (Cont’d)• Regarding the map, pigeons are able to make use of visual features in the landscape to guide them home, especially if they are in the vicinity of their loft.• There is some evidence that pigeons can hear ultra-low frequency cues radiating from steep-sided topographic features.• The most convincing evidence for the basis of the pigeon map relates to the birds’ sense of smell.• Pigeons that have be “smell-blinded” are unable to navigate home over a large distance. Similarly, birds raised in a loft with air funneled in from a 90 degree direction from the normal, natural flow learn an inappropriate olfactory map and are unable to navigate correctly away from home.
Atlantic Salmon Migration (Reliance on the Sense of Smell)
Salmon Life Cycle• The salmon life cycle involves traveling 1000s of miles, from breeding rivers and fresh water to saltwater ocean maturation areas and back again. Salmon are known for their sense of smell to home in on their spawning grounds.
Green Sea Turtles (see Alcock, p. 137-139, esp. Figs. 4.45 and 4.46)• Green sea turtles range throughout the tropical and subtropical seas around the world, with two distinct populations in the Atlantic and Pacific Oceans.• Green sea turtles travel thousands of miles from their nesting beaches to feeding areas on their annual migrations.• One population that nests in the middle of the Atlantic, on Ascension Island, travels westward to feeding zones along the Brazilian coasts, then back again to Ascension.
Green Sea Turtle Migration (Cont’d)• Scientists hypothesized that green sea turtles may be using cues from the earth’s magnetic field.• Lines of magnetic force could in theory be used by turtles to construct an internal map.• Experimental manipulation of the magnetic field did affect green sea turtle navigation; the turtles adjusted in a predictable fashion to realignments of the magnetic field• Conclusion: green sea turtles are indeed geomagnetic map navigators.
Navigation in Short• The ability of individuals to navigate over long distances, including migratory movements, involves using the same cues as they do during other forms of navigation.• It is known that the sun, stars, polarized light fields are used as compasses by birds.• Salmon employ a keen sense of smell; monarch butterflies use ultraviolet radiation as well as polarized light.• Landmark recognition is crucial for many species.• So, depending on the species, one cue may be predominant over another in one circumstance, but not another.• And integration of cues must occur for decisions to be made on the direction of movement.
Genetics of Migration• The European blackcap warbler experiments indicate that there are innate components to migratory navigation.• Southwest German blackcaps southwest migratory orientation is toward Spain.• Austrian blackcaps migrate southeast through the Balkans and Turkey.• Individual from these two populations were bred together to produce hybrids: the hybrids migratory orientation favored a more due south direction, not southwest as in the case of one set of parents, or southeast in the case of the other set.
European Blackcap Warbler• Via breeding hybrids by crossing S.W. German with Austrian warblers, Peter Berthold and Andreas Helbig demonstrated a genetic preference to migratory direction
Genetics of Migration (Cont’d)• During the period of their migration birds exhibit migratory restlessness or zugenrhue.• Under confinement some species of birds will attempt to fly in the direction of their preferred migratory route if they are kept in funnel shaped cages with wide tops that provide a view of the night sky (the starry map by which the birds use to determine direction).