Navigation and celestial imprinting

In many organisms the celestial bodies beyond Earth's atmosphere are used in navigation and many bird's use them when migrating during nighttime. During daytime many bird's also use the position of the sun to orientate themselves and ascertain direction of travel. Many experiments have been performed where the celestial bodies or relative position of the sun have been manipulated to assess the bird's ability to navigate. These manipulations cause predictable changes that highlight the processes which the bird's utilise when migration urges are expressed. 

Keeton (1974) showed how homing pigeons were able to navigate utilising the earth's magnetic field in combination with the suns position in the sky. Also, pigeons (figure 1) can use visual cues such as landmark references to remember well used paths and places of interest (food, water, safety). 

Landmark recognition: 

Figure 1. Homing pigeon.

Mammals, bird's, reptiles and insects use landmarks to recognise locations of interest (burrows, nests, water sources, food sources etc.). Learning these landmarks can occur as soon as a juvenile gains their vision or olfactory abilities where landmarks can be imprinted on the young just as their parents are (Collett & Graham, 2004).



Solar orientation:
Celestial cues like the sun are a dominating influence on the biological sphere. For humans the position of the sun is the basis of how we determine time and all the basic time-tables of our life-long behaviours. Solar orientation is utilised by a large diversity of organisms even plants! 

Figure 2. Manx shearwater. 

Manx shearwaters (figure 2) showed that they depended heavily on the position of the sun when placed in an unfamiliar location. If released on a clear-sky day they were able to orientate themselves with the sun and then return to their nests in the correct direction. However, if released on an overcast day they cannot orientate themselves and so were observed to fly around in circles until they could establish a correct direction (Lockley, 1967).

Figure 3. European starling.

The sun acts as a compass, if the organism is able to ascertain a time of day or circadian rhythm aka and internal clock. Starlings (figure 3) exhibit such an internal clock and are able to demonstrate and reproduce constant compass directions using the suns position (Kramer, 1952; Rawson, 1954). 

Figure 4. The Emlen funnel was invented by S.T. and J.T. Emlen (1966) to study bird behaviour and migratory instincts. 

Night sky (celestial) orientation: 
Lockley (1967) also discovered that warblers of many species, including blackcap warblers, utilised the constellation of stars to navigate during nighttime migration. Lockley (1967) used Emlen funnels (figure 4) (Emlen & Emlen, 1966) with a planetarium sky to investigate the bird's ability to orientate with stars. By adjusting the location of stars or speed of rotation, the experimenter was able to alter the direction of travel relative to the celestial positions. Lockley (1967) suggested that the bird's would have to have some kind of internal "chronometer and sextant" which enables the warblers to assess star patterns and travel by them; this is heavily related to the circadian rhythm just as in starlings. 

Magnetic orientation (magnetoreception):
Sensitivity to the earth's magnetic field has been observed in mammals and bird's. Fin whales have been found to respond to the geomagnetic field during migration (Walker et al., 1992). In homing pigeons (figure 1) utilise the magnetic field in conjunction with other navigational techniques, however, it is not a preferred technique, when the sun is not visible the pigeon can orientate magnetically but has been shown to be disrupted with magnets experimentally (Keeton, 1974).   


References: 

Figure 1. http://www.audubon.org/news/in-homing-pigeon-flocks-bad-bosses-quickly-get-demoted

Figure 2. http://www.animalspot.net/european-starling.html

Collett, T.S., & Graham, P. (2004). Animal Navigation: Path Integration, Visual Landmarks and Cognitive Maps" Current Biology, Vol. 14, R475–R477, June 22, 2004. doi:10.1016/j.cub.2004.06.013

Emlen, S.T. & Emlen, J.T. (1966). A technique for recording migratory orientation of captive bird's. The Auk. 83: 361-367.

Keeton, W. (1974). The orientational and navigational basis of homing in bird's. pages 47–132 in Advances in the Study of Behavior, Vol. 5. Academic Press.

Kramer, G. (1952). Experiments on bird orientation. Internation Journal of Avian Science. 94(2): 265-285. 

Lockley, R., M. (1967). Animal Navigation. Pan Books.

Rawson, K.S. (1954). Sun compass orientation and endogenous activity rhythms of the starling: (Sturnus vulgaris L.). Ethology. 11(3): 446-452.

Walker, M.M., Kirschvink, J.L., Ahmed, G. & Diction, A.E. (1992). Evidence that fin whales respond to the geomagnetic field during migration. Journal of Experimental Biology. 171: 67-78.