METHODS OF NAVIGATION
HOMING & MIGRATION
=Methods of Navigation= Regardless of whether the organism is travelling a shorter distance or extremely long distances, in order to find its way back it must have some method of navigation. These methods of navigation include: * '''Visual Cues / Landmarks''' * '''Magnetic Fields''' * '''Solar Navigation''' * '''Star Navigation''' * '''Chemical Navigation''' [image:http://i.imgur.com/g8iUup8.jpg?1] '''Visual Cues / Landmarks:''' This is where organisms remember '''visual cues / landmarks'''. Birds will often follow the topography (shape) of a coastline to their nesting sites. Certain wasps will recognise landmarks around their nest, if their nest is moved they will still return to its original location. If the landmarks are removed and placed nearby, or a similar arrangement of landmarks are placed nearby the wasps will look for their nests here (this is an example of homing as the wasps return each day to the same nest). . '''Magnetic Fields:''' This '''requires an organ capable of detecting the earth’s magnetic field'''. Iron-rich magnetite crystals which orient themselves according to the earth’s magnetic field are often found in specialised brain cells of animals that use the earth’s magnetic field as a compass for navigation. We have them too!!! And some research has shown that we too may have a limited ability to orient ourselves according to the earth’s magnetic field! The stranding of whales is thought to be caused by confusion with iron bearing land masses which interfere with this compass. [image:http://i.imgur.com/xdvFZHH.png?1] Experiments have shown that Monarch butterflies use a magnetic compass to navigate, when placed in a magnetic field that has been reversed they will go the wrong way. In autumn, monarch butterflies migrate from North America to forests in Central Mexico, where they ‘overwinter’ in extraordinary aggregations of millions of individuals. Many studies have demonstrated that these forests in Mexico are key to the monarchs' winter survival. The forest provides a unique microclimate which promote monarch survival in freezing temperatures, slows desiccation (drying out), and allows the butterflies to conserve energy stores until the spring remigration. [image:http://i.imgur.com/u3Evxxk.png?1] '''Solar Navigation (the birds & bees):''' Using the position of the sun as a compass also requires a sense of timing, as the sun will move throughout the day and the organism will need to adjust its path accordingly. Polarised light at sunrise and sunset may play an important role especially in calibrating organisms’ compasses. It is believed that the Bar-tailed godwits rely mostly on a sun-compass to navigate their journey from Alaska to New Zealand, the longest non-stop migration known, taking about one week. The godwits fly to the Alaskan tundra to breed, probably because of its abundant food supply (clams) and lack of predators. However, to avoid the harsh Alaskan winter the godwits fly all the way back down to NZ to winter there. To prepare for the flight, the godwits almost double in weight, storing fat for the journey across in which they do not stop, even to feed. Those birds that are too weak to make the journey will not get a chance to breed and as a result their genes are removed from the gene pool. Bees leave the hive each day in search of food (homing); but not only can they navigate back to the hive, they can also pass on instructions to other bees, allowing them to navigate to a food source. Bees actually communicate to each-other through dance! [image:http://i.imgur.com/9oFZv6m.gif] If a bee finds a food source (nectar) nearby (less than 50m), it will do ‘the round dance’ and this does not indicate direction, only that food is nearby. However, if a food source is a little further afield, a bee might do the ‘waggle dance’. This is a figure of eight dance in which the speed and number of waggle in the straight run between the two loops indicates the distance to the food source. The angle of this straight run (where it does its ‘waggles’) and the vertical corresponds to the angle between the sun and the food source. As if that were not hard enough the whole dance is done in the dark! This is truly a remarkable feat for such small creatures. [image:http://i.imgur.com/9TIBrKQ.png?1] '''Star Navigation''' (also known as a Star Compass) involves using the position of the stars as a compass and a sense of timing to navigate. A sense of timing is required as the stars will move throughout the night so that the organism needs to be able to adjust its path accordingly. Birds such as the Indigo Bunting use stars to navigate. This was shown in an experiment in which the birds were placed in large cages consisting of large blotting paper cones with an ink pad floor. Whenever the birds tried to escape, their intended direction could be seen on the sides of the cone. The cages were placed inside a planetarium and researchers found that the birds always oriented themselves to what they thought was “south” based on the stars projected overhead. [image:http://i.imgur.com/14FLJIF.png?2] '''Chemical Navigation:''' This is a sensitivity to a chemical or chemical gradient that allows an organism to find it way back to nesting sites. It often requires a heightened sense of smell toward a ''chemical pheromone'' (a chemical substance released by an animal that serves to influence the behaviour of other members of the same species). Ants will leave a chemical trail (pheromone) for other ants to follow, but also to help them find their way back to the nest. This is why ants are often seen in trails, following each other to a feeding site. The pheromone secreted by an ant only lasts for about 2mins. This ensures that only fresh trails to nearby food sources will be detected by other ants. Once a suitable food source has been found, the increased number of ants walking along a trail means that a larger amount of pheromone is secreted and the trail will last much longer. Ants can also use an alternative pheromone to mark out territories and more permanent trails to reliable food sources. The funny smell and taste of ants is actually the acidic pheromone they secrete.
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