Navigation How animals find their way How animals

Navigation How animals find their way

How animals find their way • Theoretically, there are three ways: 1. By pilotage – using visual cues, landmarks. Must involve previous experience. 2. Path integration (dead reckoning) – involves moving in a known direction at a known speed for a known period of time. Accumulates errors, only good for short distances. 3. By navigation – the ability to find its way over unfamiliar territory. The animal must know: the direction of home (must have a compass), and the position of all stages of the journey (must have a map).

Dead reckoning - Ants • Example – Cataglyphis fortis– an ant in the North African desert. Are able to forage covering 20 square metres in a single expedition. • They make many turns, but as soon as food is found, head back to the nest in a straight line. • To know where the nest is, they must keep a record of the change in direction (use sun and polarisation), and distance travelled at each direction (number of steps taken). • Ant experiments Ants can count

‘Step counting’ experiment • Ants legs were either shortened or lengthened to see if ants recorded distance using the numbers of steps taken. • Only the normal ants were able to navigate their way home. • https: //www. youtube. co m/watch? v=7 DDF 8 WZFno U

Animal compasses Solar compasses • Use the position of the Sun. • Sun always moves East to West. • Since the Sun moves in the sky, navigation by this means requires an internal clock ( a sense of timing). • What animals use the sun? fish, birds, sea-turtles, butterflies, bees, sandhoppers, reptiles, ants

Kramer’s experiment • Kramer experimented on starlings. • He was able to show that starlings use the sun as a compass. • Used ‘migratory restlessness’ – a caged bird shows a tendency to flutter in the direction of its migration. • Similar experiments have been done on pigeons.

Pigeon homing after a 6 h clock-shift Each dot represents the bearing chosen by a bird. Black dots are control birds, colour dots are experimentals. Dashed line is homeward. When the sun is out, clock-shifted birds go SE rather than SW. On a cloudy day, clockshifted birds do not change direction indicating that they are not using solar cues. So what if there’s no Sun? https: //www. youtube. com/watch? v=Wl 0 Ii 29 Xm. Nk

Polarisation – what is it? A light wave that is vibrating in more than one plane is referred to as unpolarised light. . Polarized light waves are light waves in which the vibrations occur in a single plane. Polarisation

How animals use polarisation to navigate • The sun is not always visible. Polarisation is used to navigate on cloudy days. • Birds/insects can locate the sun’s direction provided some of the sky is clear. • They do this by their ability to detect the plane of polarisation of the sun’s rays. • Light arriving at the top of the atmosphere is unpolarised (travels in all directions). • As it passes through the atmosphere, it becomes polarised in a plane that depends on the angle between the sun and the direction in which the observer is looking. • The animal can detect this plane of polarisation.

Honeybees – use the sun and polarisation • Polarisation - enables them to detect where the sun is even with the smallest patch of blue sky. • e. g. honeybees – keep the sun on one ommatidium of their compound eye during the outward journey and on a corresponding opposite ommatidium on the return journey. • Task: complete BZ pgs 18 -19 ‘Sun Compass Navigation’

The waggle dance • Bee indicates where a food source is to the hive, by doing one of two dances. • Round dance – points directly to a food source within 50 m • Waggle dance – bee traces a figure 8. The axis of the waggle (in regards to the vertical nature of the comb in the hive) indicates the direction of the food in relation to the direction of the sun. • The number of waggles indicates the distance. • Fewer, slower waggles the further away the food is. What's the waggle dance? Why do honeybees do it? The waggle dance of the honeybee

Using the stars • Animals that migrate at night can’t use the sun. • Presumably, birds can memorise some of the constellations. • Birds use the South Celestial Pole (the point in the southern night sky in which stars seem to rotate).

• The knowledge of the night sky is learned, not innate. • A stellar compass does not require an internal clock as the direction of the SCP does not change.

Experiments on Stellar Navigation • Caged birds were put inside a planetarium (mimics the apparent movement of the stars). • At the time of their normal migration, birds demonstrated fluttering in the direction of their normal migration. • When the planetarium was rotated 180 degrees, the direction of the fluttering also reversed. How do birds navigate?

Using the earth’s magnetic field • Animal magnetism • Earth has a liquid iron core which generates magnetic fields. It acts like a giant bar magnet. • Animals are able to use the magnetic field generated by the earth’s core to navigate. • Not only does the field provide a compass, allowing animals to orient themselves with regard to north and south; it seems that the Earth’s magnetism can also serve as a kind of map. • Animals that use this – mice, bats, pigeons, sea-turtles, hammerhead sharks, amphibians, crayfish, bees

• Birds’ compass sense is based not on the polarity of the Earth’s magnetic field, but on the angles at which the field lines intersect the planet’s surface, known as the inclination. • Depending on how the inclination of the field lines change as they fly, the birds perceive whether they are heading poleward or “equator-ward” and gauge their approximate distance between the magnetic equator and the nearest magnetic pole.

Anomolies • Magnetised rocks in the crust give rise to local variations called anomolies. • These can cause birds to go off course and whales to strand.

Magnetic field pigeon experiment • Bar magnets were placed on a group of pigeons heads, with no magnets on a group that were the control. • On a sunny day, the magnets made no difference to either group. • On a cloudy day, the group with magnets were less able to find their way home, with the control group being unaffected. • This suggests their ability to use the magnetic field was disrupted by the presence of the magnets.

Magnoreceptors • Magnetoreception (also magnetoception) is a sense which allows an organism to detect a magnetic field to perceive direction, altitude or location. • Any magnetic receptor must contain material sensitive to a magnetic field, eg magnetite. • Magnetite has been found in magnetotactic bacteria, honey bees, homing pigeons, rainbow trout, dolphins. • Human made problems with migration: Lost in migration

Chemical navigation • Dogs are able to follow scents to find home. • Ants leave chemical trails for other ants to follow. • 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). • There is a cocktail of chemicals in the freshwater streams that migratory animals recognise eg eels, salmon • Salmon experiment – salmon that had their noses blocked missed a crucial turn in the river.

Sound used as sonar • Echolocation is the use of sound waves and echoes to determine where objects are in space. Bats use echolocation to navigate and find food in the dark. To echolocate, bats send out sound waves from their mouth or nose. When the sound waves hit an object they produce echoes.