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Deforestation can lead to changes in the way birds communicated. Deforestation is the clearing of forest for human activities such as expansion of housing schemes, farming, mining, making pastures. Deforestation occur everyday as the expanding population of developing countries seeks the trees, the land itself or its minerals. The rain forest is being cleared at an alarming rate of 78 million acres per year. The removal of trees causes a multitude of negative effect on the natural environment. The habitats of many species of organisms are destroyed by the removal of trees. Since there exist interrelationships between organisms within an ecosystem, all are affected. This change in the environment can lead to changes in the behavior of birds. Some when possible migrate to other similar habitat. Extinction may occur but others might remain and seek to adapt to the changes. Adaptation to the new environment includes change in loudness and pitch of songs. These changes become necessary as a result of the changes in the physical environment.
Birds well developed sense of sight and hearing, along with vocalization are used for the transmission and receiving of signals between the birds. Bird's vocal sounds include songs and bird call. Bird calls are usually shorter than the 'musical' songs. Songs can also be distinguished by the difference of inflection, length and context. The songs of birds are usually longer and more complex. They are used during courtship and mating. However calls are used to signal alarm or keep member of a flock in contact as the move. When the classification of songs and calls are based on function, then shot vocalization like those of pigeons are considered songs. Under that method of distinction drumming of woodpeckers and sounds of the snipes wings are also considered songs.
While birds of the order Passeriformes are well developed in their ability to produce songs, others are voiceless but produce percussive and rhythmic sounds. The storks are great at clattering their bill, some manikins (Pipridae) produce mechanical sounds by stridulation - the way insects produce sounds. These 'instrumental sounds' are now called sonate. It is the act of producing non-vocal sounds to communicate using non-syringeal structures such as the bill, wings, tail, feet and body.
People who rare song birds in on the coast land Guyana can often be seen placing the caged bird next to road side or high ways. They often claim that they are taming the bird. It is very likely that certain aspects of the songs eventually changes as these birds are exposed to the openness of the landscape and noise of roadside traffic. This custom has passed on to other bird keepers. Other birds living freely on land cleared of forest such as on farms or in urban environment with buildings and urban noise would also change certain aspects of their song in order to be effective.
How birds vocalize
The syrinx is the vocal organ of birds. It is a bony structure at the bottom of the trachea. The syrinx and sometimes a surrounding air sac resonate to sound waves that are made membrane over which the bird forces air. Pitch of the sound can be controlled by changing the tension of the membrane. By changing force of exhalation both pitch and volume can be changed. The two side of the trachea can be controlled independently and this allows some species to produce two notes at once.
Reasons for producing sounds
Mainly the mail species are vocal. The quality of a bird's song can serve as a good indicator of its health and fitness. Diseases affect the characteristics songs such as how often they sing. Fitness can also be demonstrated by a male bird's ability to hold and advertise a territory by using songs. The songs therefore allow the female to select a health and fit male during mating season.
Bird call can be between the same species or across species. The mobbing call is transmitted across species to alert other of the intrusion of a predator such as an owl. The sound is characterized by broad frequency spectra which enables different species of birds to detect it. It also has sharp onset and termination and is repetitive. These characteristics allow the source of the sound to be easily traced to a specific location.
Birds are able to identify each other through their call. Birds that have monogamous mating are able can distinguish its mate form the others. Birds that nest in colonies are able to locate their chicks. Some sound so distinctive that some researchers are able to identify certain individual while carrying out ecological studies.
Some birds produce vocal mimics of other birds or even other animals. This may play a role in warding of predators, being able to forage with other species and can also pay a role in sexual selection.
The plumage of bird in communication
Birds are usually very colourful. Their visual system is highly developed. Apart form their role to aid flight feather also are used to communicate signals. Ultraviolet sensitive cones are found in the cone cells, as well as green red and blue ones. This make them able to perceive ultra violet light emitted form some feather which is important during courtship. To the human eye the sexes of bird may look similar in plumage but this because the human eye cannot detect the ultraviolet patches that distinguish male form female. The plumage of bird also can allow a blend into the environment this can be seen in the African Scoop Owls which has a colour similar to tree bark.
The arrangement of feather and the appearance also varies according to the age and social status. The juvenile may go through several molts before acquiring the breeding plumage at maturity. After the breed season birds the return to non-breeding plumage. Plumage can also be used to assert social dominance this can be seen in the King vulture. Ritualised display of feather may also signal dominance or submission. This is important during courtship and the formation of pair-bonds. Very elaborate display occurs during courtship.
Importance of forest to birds
The trees allow birds to perch when sleeping at night or resting during at interval during the day. Most birds are active in the early morning and seek shade during the mid-day. This pattern may be related to the availability of food and conservation of energy during when the temperature of the day is higher. The trees provide a place to build nest away from flooding and being away from some other animal which may seek the eggs or chicks. Plants also provide the materal needed to construct nest for some birds.
The tress provides food for fruit eating birds and nectar other birds. Birds are specialized to eat certain types of fruits and feed on certain types of flowers. Parrots can crack hard shell of nuts and toucans prefer fleshy fruits like mango and some other smaller fruits.
The dead leaves letter forest floors and provide suitable habitat for insects, there larva and other invertebrates. Some birds thrive on these high protein diets and are protected by the over growth of tall tress. Other insects may live on live on the trees themselves and these may be utilized by the woodpecker for example.
How the forest aids in bird communication
The sound frequency at which birds hear is from 50 Hz (infrasound) to above 20 kHz (ultrasound) they are most sensitive to sound between 1 and 5 kHz. Sounds are produce by the vibrations of air particles. It travels away from the source in the form of longitudinal waves. Like light, sound is subjected to refraction which is the spreading out waves as they pass through a narrow gap or changes speed. The waves of sound can change speed when the air is hotter. If the air is cooler close the ground the sounds waves will be bent up wards. In a deforested land the songs of bird will bend up as it reaches the hot raising air close the ground.
With tall tree shading the ground and trapping moisture the level of humidity be higher than that of open environment like on a farm land. Sound waves travel more swiftly and efficiently in water than in dry air therefore the quality of songs of bird is likely to be affect by dry air which is more common in deforested areas.
Sounds are governed by the law of reflection. On a smooth hard surface the angle of incidence is equal to the angle of reflection. Curved surface like parabola causes sound waves to bounce out in a straight line. An echo is heard when sound waves are reflected back to the ears. Everything absorbs some amount of sound energy. Material with holes absorbs the most amount of energy. In a forested area while birds are making sounds these phenomena will occur. The sound will be reflected by tree, some will be absorbed and there will also be echoes. Where the forest is removing the sound continues to travel in all direction.
Deforestation will impact the vocal communication of birds as well the plumage. The range of frequency birds calls in a forested land differs for that of open land or urban landscape. It can be suggested that narrow bandwidth, low-frequencies modulations, short elements and inte-elements would be found in habitat of complex vegetation which would absorb sounds. High frequencies, broad bandwidth, high frequency modulation (thrills) and shorter elements and inter-element would be found in deforested area. It has been observed that some birds sing louder at higher pitch in urban area, where there is low ambient low-frequency noise.
Birds that blend with the in natural environment will be outstanding which would affect the predator-prey relationship possibly leading to extinction.
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