Deforestation is referred to as the removal of the natural environment particularly trees on an unsustainable rate, on large scales, without replacing said trees. Deforestation occurs in all regions of the world, from the tropical to the sub-tropical regions and to temperate regions, hence occurring in rainforests to tundra respectively. Deforestation occurs for a number of reasons, these include mainly for; (1) land used for development purposes, (2) the timber products use in building and furniture construction and fire wood in temperate regions, (3) the use in agricultural purposes e.g. clearing of forest in Brazil for production of soybeans and the removal of forests in Mexico for cattle rearing and (4) large and small scale mining operations. Deforestation has been documented to have a lasting impact on all organisms present in said area including plants. But the significant impact on wildlife whether it is on the population of the wildlife or the behavioral aspect of these organisms.
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In this essay the impact of deforestation on bird communications is assessed. When combined together, forest around the world hold majority of the approximately ten thousand species of birds known today. Forests whether it be rainforests or coniferous are essential to bird life, they are adapted to living in these particular habitat found in these forests.
Communication is essential and necessary in the everyday activities of these birds. Birds can engage in communication in two way, these include; (1) vocalization, which includes bird songs and bird calls and (2) signaling (display) which includes feather ruffling, elongating their necks, beak movements among other activities. Some birds even communicate by producing sound unique only to them during flight; known as flight noises one such example is the hummingbird produces a unique sound with their wings.
Vocalization includes song and calls. Songs are usually sex hormone(s) driven and can only be heard during breeding seasons. Birds have an auditory feedback system that birds develop from young. Birds are only capable of hearing songs and calls memorized from young. Songs are usually necessary for mating and are primarily hormone driven, it also aids in strengthening pair bonds and defending nesting territory. Songs are of two types; (1) primary songs, produced by males and are usually loud and (2) secondary songs, the purpose of these is not fully known. There is a link between deforestation and bird songs, hence its impact on bird communication. Birds as research has shown usually mate when conditions are favorable whether these conditions be environmental or otherwise, either beginning of the rainy seasons or the end of the rainy seasons or when there is an abundance of food, so chicks can easily fed whether altricial or precocial. This taking into consideration that many forests birds will be localized or specialized feeders or both, deforestation will have an impact on bird songs. Since songs are usually use in mating, when these birds habitats are disturbed or destroyed to the extent that any of the factor mentioned above dependant on mating will affect bird songs and hence communication.
By destroying the trees that specialized birds depend on feeding, there will be a dwindle in the abundance of food, therefore, these birds that depend on these tree will recognize this, sex hormones will not be triggered due to this, thus reproductive behavior will be affected directly related to songs not being produced and ultimately have a negative impact on bird communication. Birds will respond to the decrease in food which many use as an indicator for mating in a negative way, if there is only enough food for available for the bird on each day, energy conservation will be the number one priority and anything that requires energy will not be taken into consideration, hence, mating will be put off and the communication that necessary for this will be nullified, thus bird communication is therefore impacted.
Disturbance and destruction of these bird habitats will also eventually lead to birds relocating from a familiar to an unfamiliar territory, birds especially if they are specialized to a particular habitat will be affected in terms of mating. If relocated the type of environment may not be conducive for bird to commence mating, this may be due to several reasons including availability of food, type of food, mating and nesting sites, the type of trees necessary for nesting and the type of predators present in that particular new environment. Conditions again will not be favorable for mating, hence communication (song) necessary will be second natured, or the sex hormones necessary to start the imitation process of mating will not be triggered due to unfavorable conditions. Bird communication again will be impacted again. Dispersal of birds due to deforestation will also affect communication.
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Although it causes relocation, birds may be familiar with the new environment, food supply may be adequate, nesting and mating sites available and other conditions may be right, however, due to dispersal of birds, male and female birds may be relocated to different areas, so songs sang by male birds to initiate mating may go unanswered because the pitch of the songs might not be high enough for female birds to hear. Thus, hampering communication between the species. It has also been documented that, with creditable evidence that many birds especially ground dwelling birds usually mate depending on the time of the seasons, birds usually mate before and after the rainy seasons. It has been documented also that removal of trees on large scales, usually have an impact on the season, especially in rainforests, cutting down of trees usually have an impact on the hydrological cycle. Many processes of this cycle especially precipitation will be affected. Beginning or end of the rainy seasons usually serve as an indicator for mating, again sex hormones will not be triggered of be delayed since the indication necessary for mating will be hindered. Bird songs which are necessary for mating for many birds will be impacted and hence bird communication overall.
A study by Hans Slabbekkoorn and his colleague entitled 'HABITAT-DDEPENTENT SONG DIVERGENCE IN LITTLT GREENBUL: AN ANALYSIS OF ENVIRONMENTAL SELECTION PRESSUERS ON ACOUSTICS SIGNALS' found that Antropadus virens changes song depending on their environments, while this is a good trait to withstand environmental changes imposed by deforestation, the draw back is for those birds that change environment and songs cannot change their frequencies as suggested by the authors, the these birds will be at a disadvantage if mating is to occur in this new environment. The authors base that environmental conditions is responsible for changes in songs of the Greenbuls. This can ultimately lead to a disruption in communication if birds are continuously changing their locations due to deforestation. Trees are necessary for many song birds during mating seasons since the trees will provide singing posts for many specialized birds and nests are usually located near singing posts. Removal of trees will leave many specialized birds without the access of a proper singing post, thus affecting bird communication.
Another way that birds use vocalization to communicate is through calls. Unlike bird songs which are only heard during mating seasons, bird calls are heard throughout the year. They are short notes that may sound erratic at times but they are not haphazard. Calls are primarily functioning in location, identification (not necessarily sexual), feeding, coordination and alarm among other functions. Each bird call has two specific functions (1) threat calls and (2) alarm calls. Threat calls are usually "intended in the influence of the behaviour of other birds of the same species," (http://birdsahoy.org/birdsong/#toc), and alarms are used to indicate danger ((http://birdsahoy.org/birdsong/#toc). Deforestation will impact birds songs specifically if the birds are localized or in some cases endemic. Deforestation will cause dispersal and relocation of bird species to different environment as stated previously. By doing this, birds will generally go to areas with similar habitat, but the area may still be unfamiliar territory.
Birds along with being able to communicate with members of their species also learn to communicate with different organisms in their environment, especially predators and other organisms they form a symbiotic relationship with. By changing habitat, due to deforestation birds will lack the necessary skill to communicate the presence of predators to fellow birds of the same species, since method of predation may differ in the new environment. Birds will lack the necessary mechanism to identify the new predator and in this case since they will lack the ability to identify the new predator, alarms may not be an adequate response to deal with the new threat.
Again the link between birds communications in this case bird calls (alarm) and the effect that deforestation has on it is established. With bird threats, deforestation as stated previously will cause dispersal of the species and threat by birds to others members may be nullified or intensified for several reasons that may include: (1) abundance of food may vary thus intensifying bird threat, (2) nesting may be limited or (3) dispersal may cause bird numbers to dwindle thus reducing or even nullifying threats. Threat may also intensify food supply is limited in the new environment especially pre-mating seasons, when many forests birds will rely on best fruit for enhancing colour to maximize chances of attracting a mate also the most energy efficient foods to maximize singing abilities in terms of duration and amplitude of songs. For this particular reason deforestation may have both a positive and negative effect on bird communications.
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Display or visual communication is an important skill forests birds develop and is unique to many different species of birds. Again birds that are localized or endemic to a particular environment may be familiar with the type of threats they may encounter and thus have devised several display mechanisms that allow these threats to pass. However, since deforestation involves destruction of habitat, birds will relocate to different environments and as such new threat will emerge, tactics and other behavioral mechanisms which may have worked to nullify a familiar threat may not work against a new predator, since the mechanism of the display or behavior may not effectively work against the new threat. Again bird communication is therefore impacted by deforestation. Another aspect that birds rely on display as a form of communication is in mating. Many male forests birds use colour of their plumage to attract a female mate.
This usually involves birds with the best and brightest colour of their plumage to have mate, this require access to the best food available since colour would indicate which male will have access to he best food. Many birds as stated above are specialize feeders to a particular habitat or location, deforestation causes destruction of many of these habitat and the trees used by these specialized birds. Deforestation cases relocation of birds to unfamiliar territory and different types and abundance or food necessary for male birds to have the necessary plumage to use as display for mate attraction. Again deforestation impacts bird communications as related to the above. Poor access to food will lead to poor colour of the plumage which hinders mate choosing by females. Also there may not be any display at all due to the type of food present in that area, it may not be conjunctive for the bird to consume unfamiliar food just in order to have access to a better plumage necessary for mate attraction.
These are the possible way that deforestation can have an impact on bird communication whether it is a positive or a negative impact as stated in this essay. Deforestation has both an indirect and direct impact on bird communication as mentioned previously.
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- SLABBEKOORN, Hans, et al, HABITAT-DDEPENTENT SONG DIVERGENCE IN LITTLT GREENBUL: AN ANALYSIS OF ENVIRONMENTAL SELECTION PRESSUERS ON ACOUSTICS SIGNALS, 2002, date accessed 14/11/2009.