How do birds navigate?
The extraordinary ability of navigation possessed by birds has been a topic of discussion among historians since ancient times. This ability enables them to carry out the long distance migrations with precision. With a number of theories proposed over the subject, the one that proves that magnetism is the most crucial factor in the navigation process of birds is more plausible. The theory that birds use smell to navigate does not make for a strong argument since birds does not have good sense of smell unlike mamals.
It has been found through research that birds acquire their most of the information through the magnetic compass or through their magnetic sensory system. Other points out, the role of the traces of atmospheric gases that the birds detect by using their olfactory system (Wallraff and Meinrat). Given that the historical findings over the subject have had less of an empirical data to conclude anything convincingly, the modern theory such as that of “lagana” as being an important factor in the navigation of birds makes more sense.
During the period of migration of birds, they use cues gathered from the celestial sources, magnetic compass and endogenous migration program (Wehner). The magnetic sensory system of the birds has been observed and researched to be controlled by the lagenal organ which seems to play a crucial role in a magnetic sensory system of the birds. The lagena helps in the detection of the magnetic sensory signals from the earth’s magnetic field which helps them to return to their homes.
Researches confirm this postulation of magnetic sensory compasses which the birds use to detect their direction and for navigation. Any of the disruptions in the magnetic sensory system of birds can cause problems in migration or their returning back home.
This proves the important role of the magnetic sensory system in helping the birds navigate. The use of the olfactory cues for navigation is still a debate able issue and does not hold strong grounds. Researchers tried to prove it through different experimentations but are not able to develop strong relationships of olfactory cues to navigate. though, it may be used for the purpose other than navigation by the birds.
Besides this it has been also proposed that the birds possess the spatial ability of creating visual landmarks and the magnetic field of the earth. But after decades of study, this mystery of how birds navigate continues to remain elusive.
In this paper I shall expand my arguments on the topic on the four statements;
The theory that birds use their magnetic sensory system through an inbuilt organ ‘lagena’ is more plausible as compared to the other theories proposed over the subject.
It is essential for almost all animals to polarize through space within the framework of some direction. This enables them to maintain their movement in a specific direction in relation to their environment. The birds navigators possess an internal biological compass which might be sensitive to the position of the sun, or the stars or the magnetic field of the earth. Out of these the sensitivity of the birds biological compass to the magnetic field of the earth seems to be more plausible and is now well established by the researchers ((Bingman, Jechura & Kahn).
The experiments conducted on homing pigeons and homing pigeons show that they possess the geomagnetic orientation, when a shift in the changes in the ambient magnetic field lines takes place in the conditions when they have to rely on the non-visual cues for orientation (Wiltschko & Wiltschko).
Another study proves that the lagenal nerves play a role and interact with the magnetic field of the earth for navigation in birds. The results of the experiment showed that the homing pigeons whose lagenal nerves or lagena organ was interfered through the magnet were either lost or a significant delay occurred in their return while those in the control group returned to their destination almost within 30 minutes after they were released from their location (Harada). This speaks in the favour of the role played by lagena in the magnetic sensory system of the birds.
Another study supported the magnetic orientation in birds. According to the study, animals and birds make use of the magnetic field of the earth in different ways. The study indicated that the birds and other such animals use the magnetic receptors supported by the earth’s magnetic field to navigate. The available evidence from different studies suggest that birds use the chemical compass which has a basis in a radical pair mechanism along with magnetite particles to navigate (Wiltschko & Wiltschko ).
Besides these studies other supporting evidence for the magnetic orientation in birds comes from the study of Wiltschko & Wiltschko (1996). The study had been conducted on almost 18 species of migrating birds with respect to the properties of their functions. They were found to posses the compass of inclination. This inclination compass provides them with any information from the earth’s magnetic field lines and gives them an ability to distinguish between pole ward or equator ward navigation.
There has also been an evidence in favour of the presence of the sensitivity of the geomagnetic field which is used by birds for navigation (Beason). The majority of studies conducted during the period of migration, confirmed that the magnetic field holds the position of primary orientation cues as compared to the celestial or astronomical cues (Able, Åkesson , Wiltschko , Wiltschko & Wiltschko).
Other such theories related to the use of astronomical or celestial cues do not provide enough support and experimental evidence to prove their standpoint scientifically. They have a weak basis in their support.
Another proposition is that,Birds use magnetic earth signals to return to their homes and the organ lagena plays a crucial role for that matter.Many experiments have been done to find out the behaviour of homing and navigational abilities in birds. There has been a substantial support in favour of the existence of the magnetic receptors in the different organs of the birds which are activated by magnetic stimulations from the earth’s magnetic field.
The studies also suggest that there is an organ called lagena which is the part of the inner ear plays an important role in the electromagnetic orientation of the birds ( Wu & Dickman). Another experimental study supported the role of the lagenal organ in the spatial orientation of birds. Behavioural experiments were conducted on the pigeons to find out their homing abilities. The experiment was done by sectioning the lagenal nerves of the pigeons or by interfering the lagenal functioning by using the magnet. A total of 51 pigeons of the same race were used out of which 21 were placed in the experimental group while 30 were used as a control group. The group of treated birds either unable to find their way back or there was a significant delay in their returning as compared to the control group who managed to return back just after 30 minutes from the time they were released.
The results of this experiment clearly demonstrate the magnetic influence on the function of the laguna in connection to the navigational ability of the birds (Harada). This showed that lagena significantly plays a crucial role in the magnetic sensory system of the birds.
There has been experimental analysis which rightly proves that once there is any interruption or disturbance in the magnetic sensory system of birds, it becomes difficult for them to migrate to other places or come back home.Experiments conducted on homing pigeons with the magnets attached on their back resulted in the disruptions in the ability of the birds to detect the magnetic field of the earth and it leads them towards the loss of proper behaviour of orientation under the conditions of overcast (Keeton).
In a test, conducted to check the magnetic sensory system of the birds, a tunnel was created and birds were trained to jump on the platform on the other side of the tunnel in the absence of the magnetic field and also to jump on another platform in the presence of a magnetic field. They were also given reward in the form of food and punishment in the form of time penalty. The birds were able to make the choice correctly for almost 55-65% of the times which is quite high if they had simply been guessing. It has also been found that if the magnetic sensory system of the birds have been impaired using the lignocaine, it leads towards disorientation of navigation in birds (Mouritsen & Ritz).
In addition to this, a study was conducted on homing pigeons in which the magnetic domains in the head region of the birds were altered by demagnetizing the birds, magnetizing them by using a strong magnetic field and also by exposing them to the strong magnetic gradient. The results which were obtained during the overcast sky suggested that the birds whose magnetic sensory system were demagnetized were unable to locate their bearings properly ( Walcott, Gould & Lednor).
Another theory propose that birds make use of the olfactory cues detected through special olfactory receptors, for navigation cannot be substantiated with tenable argument . The fact remains that birds do not have that good sense of smell as mammals.
The sense of smell is referred to as the olfactory perception. The olfactory perception in most of the bird species has been found to be poorly developed and they cannot use it for proper navigation. In some other cases, the sense of smell is used by birds for any other purposes such as for mating by Drake Mallard and Starling which uses his smell sense to find a material for its nest which disinfects it ( Smell).
Though there has been some evidences that odour is partly used by pigeons and doves for the purpose of navigation but this is not strong enough to prove the point. The studies on this subject shows that most of the birds use olfactory receptors for the other purposes rather than for navigation. The visual, magnetic and other sensory cues are more important in the navigation of birds as compared to olfactory cues. The birds do have sense of smell but it’s not as developed as that of mammals. There is not enough supporting evidence available to prove that the birds make use of the olfactory perception in their navigation.
Taking into consideration, all the presented information and researches in the above discussion it stands proved that the birds rely to a significant extent on their magnetic receptors for the purpose of navigating through space and the lagenal organ plays an important part in this navigation.
The magnetic field of the earth provides the electromagnetic cues to the birds which they detect through their magnetic receptors present in their physiology. Any damage to their magnetic receptors can cause problems in their navigation ability.Magnetic navigational system is one of the great and fascinating mystery of nature. Most of the species of the birds do have olfactory perception but it’s do not play a significant part in their navigation. In fact, it is used more for the purposes other than navigation.
There is a need for more research and study in the field of olfactory perception of birds to develop its experimental relation to the bird’s navigation ability.