Human caused deforestation

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Introduction

Deforestation - is defined as "Deforestation is the loss or continual degradation of forest habit due to either natural or human related causes. Agriculture, urban sprawl, unsustainable forestry practices, mining, and petroleum exploration all contribute to human caused deforestation. Natural deforestation can be linked to tsunamis, forest fires, volcanic eruptions, glaciation and desertification" [www.experiencefestival.com ]

Forests provide habitat for wide variety of birds therefore it structure and degradation has a major effect on information transfer between individuals .[Nicolas Matevon et al...]

Communication, i.e. signal-based information transfer between individuals, supports social relationships in animals. In a classical view, a communication process can be described as follows: the signal, supporting information, is produced by an emitter and received by a receiver following propagation through a transmission channel. However, in most natural situations, animals belong to a communication network where any individual can act both as an emitter and a receiver at any time and where any information exchange between two interacting individuals can potentially be subject to eavesdropping by other members of the network . .[Nicolas Matevon et al...]

Birds communicate in a variety of ways, They produce meaningful communications by their facial expressions, beak movements, feather ruffling, elongating their necks, crouching, bouncing, and flapping their wings. Although each species has its own body language, many different species interpret movements in the same way. For example, various species interpret an upward thrust of the beak as expressing the intention to fly, and the lowering of the breast as a warning of danger. Also, several species perceive raising the tail feathers as a threat, or displaying bright colors atop of the head as a declaration of the intent to attack. Via facial expression, birds can convey a variety of messages to those around them-negative feelings such as dislike and resentment, as well as positive ones like pleasure, enthusiasm and curiosity. [www.harunyahya.com/articles/language_of_birds.php]

Besides communicating by means of body language, birds produce a great variety of sounds to communicate with other members of their flock, neighbors, or family members. These range from short, simple calls to songs that are surprisingly long and complex. Sometimes birds such as the green woodpecker use different instruments or, like the American woodpecker, use special feathers to produce sound. Usually, birdsong is not composed of randomly produced sounds. Songs are exceptionally diverse melodies of specific meaning, sung for a purpose, and are much more complex than the calls used for signaling. They are generally used by males to advertise and defend a territory, or in courtship. It is also believed that songs serve a social function. When a pair is building their nest, they also establish communication by song. Experiments on caged birds have also demonstrated that birds find it easier to learn songs if another bird is present, but out of sight, in another cage. [www.harunyahya.com/articles/language_of_birds.php ]

Birds also communicate through scents, although since their sense of smell is poor, their communication is based mainly on sound and sight. At times of poor visibility, as at night or in dense foliage, sound is most advantageous, and is also the ideal method for long-distance communication. If conditions are right, birdsong can be heard for up to a few kilometers.

[www.harunyahya.com/articles/language_of_birds.php ]

In addition to song, birds also have conceptualization and communication skills. In certain circumstances, they demonstrate talents equivalent to those of children of primary-school age, learning series of words and other means of human communication through social interaction. When alone, these parrots play vocalization games and when in the company of people, they join vocalizations together to produce new assemblages from existing sequences of speech. [www.harunyahya.com/articles/language_of_birds.php ]

For this communication to be effective birds require excellent vision and if this is impaired excellent hearing. [www.harunyahya.com/articles/language_of_birds.php ]

Habitat structure and bird song acoustics

Habitat structure has been considered as a main factor shaping the evolution of bird song acoustics. [G. Boncoraglio et al...].According to the ''acoustic adaptation hypothesis'', the general structure of animal signals will differ dependingon general features of the habitat .[Nicolas Matevon et al...]Based on the different patterns of degradation in relation to habitat structure , the AAH predicts that songs with low frequencies, narrow bandwidths, low frequency modulations (whistles), long elements and interelement intervals should be prevalent in habitats with complex vegetational structure, while high frequencies, broad bandwidths, high frequency modulations (trills),short elements and inter-element are expected in habitats with herbaceous coverage. [G. Boncoraglio et al...].

In their study captioned "Habitat structure and the evolution of bird song: a meta-analysis of the evidence for the acoustic adaptation hypothesis" Giuseppe Boncoraglio and Nicola Saino indicated results consistent with the hypothesis.The main result of the meta-analysis is that all the four song frequency features we considered and tested showed differences between open and closed habitats that were consistent with the predictions of the AAH, as populations or species from closed habitats were found to sing at lower frequencies and frequency ranges than those from open habitats. Only peak frequency was found to differ between habitats in the direction predicted by the AAH when the analysis was restricted to the Oscines. . [G. Boncoraglio et al...]. Susceptibility to degradation is larger for high frequency songs and, other things being equal, habitats with structurally complex vegetation determine larger degradation and thus selection for less degradable, low frequency songs. The fact that the strength of the effect of habitat on song is most clear for peak frequency compared with other frequency features is consistent with the general idea that selection for broadcast maximization has played a major role in shaping the evolution of song with respect to habitat. Peak song frequency represents the frequency at which most energy is discharged and therefore directly affects song broadcast range because intensity at peak frequency will be larger than intensity at other song frequencies at any given distance from the utterer. Song at peak frequency will thus be audible at larger distances from the sources than song at other frequencies. Thus, closed-habitat species may have evolved low peak frequency songs because low frequencies are less attenuated than high frequencies in closed habitats and therefore allow for song being broadcast farther. [G. Boncoraglio et al...]

Biologist Elizabeth Derryberry found as part of her dissertation research at Duke University, that as vegetation reclaimed formerly cleared land in California, Oregon and Washington over the last 35 years, male white-crowned sparrows have lowered their pitch and slowed down their singing so that their love songs would carry better through heavier foliage.

She compared recordings of individual birds in 15 different areas with some nearly forgotten recordings made at the same spots in the 1970s by a California Academy of Sciences researcher, and found that the musical pitch and speed of the trill portion of the sparrows' short songs had dropped considerably. She then used archival aerial photography to see how the foliage had changed in a subset of those spots, and found that the one population whose song hadn't slowed down lived in an area where the foliage hadn't changed either.

The results add to a growing body of evidence that the acoustic and visual communications of animals change with their habitat.

The physics is clear, but the biology is a little less certain. A lower, slower song suffers less reverberation in denser foliage and will be heard more accurately. In turn, that means it is more likely to be copied by young males who are choosing which song they will learn. Over generations, that should cause the song to slow down and drop in pitch as the foliage changes.

[www.sciencedaily.com­]

Further research by Amanda Jobbins into bird song has found that lower frequencies travel the farthest regardless of habitat (Wiley and Richards 1982) and higher frequencies have a greater tendency to be scattered by foliage in comparison to lower frequencies (Wiley 1991). These characteristics imply that high frequencies may be constrained by habitat (Wiley 1991). Furthermore, higher frequencies are affected by different levels of background (ambient) noise (Ryan and Brenowitz 1985). In terms of habitat, closed habitats may cause greater attenuation (reduction) in songs, and reverberation is thought to influence the length of notes and the amount of time between notes (Tubaro and Segura 1995). Therefore, birds that live in habitats with numerous scattering surfaces (e.g. leaves, branches) may adopt the following strategies: avoid using rapidly modulated (vary amplitude or frequency) signals; use shorter notes; and put more space between notes to mitigate reverberations []

Conclusion

Some of the major functions of bird song include mate attraction, species recognition, and the establishment and defense of territory. Bird song is also closely linked to individual fitness; therefore, songs that maximize effective communication of signals should increase the fitness of that individual.[ Amanda Jobbins ]

The AAH is the only comprehensive hypothesis that relates song features to habitat structure, based on the assumption that songs are shaped by habitat-driven selection so to enhance sound propagation and inalterability under the constraints imposed by physical structure of the habitats. However, it neglects any evolutionary trade-off between signal transmission and energetic costs of signalling, and the role of other biotic selection factors, such as predation and parasitism, on bird song evolution. In their meta-analysis, Giuseppe Boncoraglio and Nicola Saino supports the AAH, but states that habitat structure only weakly predicts the acoustical properties of bird songs. Thus, other potentially relevant factors should be included in realistic models of the evolution of bird song acoustics.

Keep the afore mentioned information dealing with "habitat structure and bird song acoustics" in mind it would be safe to assume that in deforested areas birds songs would be less subject to degradation and reverberation , hence communication will be subject fewer constraints, also communication via visual displays should occur with increased frequency. Whereas In the dense vegetation of temperate or tropical forests, communication processes are constrained by propagation-induced modifications of the transmitted sounds. The presence of leaves, trunks and branches induces important sound reverberation and absorption leading to diminution of the signal energy as well as qualitative modifications.

Reference

  • Author unknown. A Miracle of the Living World: Communication and Signaling in the Language of Birds. Retrieved November 3, 2009, from http://www.harunyahya.com/articles/language_of_birds.php
  • Elizabeth Derryberry. Bird Songs Change With The Landscape. Retrieved November 3, 2009, from http://www.sciencedaily.com­ /releases/2009/05/090520114710.htm
  • Author unknown. Deforestation. Retrieved November 3, 2009, from www.experiencefestival.com
  • Boncoraglio, G. and Saino, N. 2007. Habitat Structure and the Evolution of Bird Song: A Meta-Analysis of Evidence for the Acoustic Adaptation Hypothesis. Functional Ecology, 21, 134-142 Retrieved November 3, 2009, from www.ingentaconnect.com
  • NICOLAS MATHEVON, THIERRY AUBIN, TORBEN DABELSTEEN2 and JACQUES M.E. VIELLIARD. Are communication activities shaped by environmental constraints in reverberating and absorbing forest habitats? Retrieved November 3, 2009, from :www.scielo.br/pdf/aabc/v76n2/a11v76n2.pdf
  • Amanda Jobbins. Effect of Habitat on Bird Song. Retrieved November 3, 2009, from www.ingentaconnect.com

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