Migrations Of North American Birds Essay, Research Paper
1.Introduction:Population has been increased dramatically for last two decades, and at the same time, the area of wilderness area has been decreased (Geography 210 2001 and The Wilderness Society 1999). Human population, at the same time, distributed broader, which affected the number and size of the fragmented area in the wilderness area (Peter et al. 2000). Migrant birds tend to need large breeding habitat area (RRBO 1997). In this paper, I will discuss how the bird population affected by fragmentation and reduction of the wilderness area caused by human interactions. 2. Assumption:Fragmented area will affect the structure and quality of the corridor thus the number of the wildlife, especially I focus on migrant birds, that use corridor will be effected. 3. Description of general characteristics of migrant birds:4. How actually correlated to fragmentation and birds: Many researchers think many Neotropical migrant bird species are declining at local or regional level because of habitat loss or fragmentation (Friesen et al. 1995 and Donovan et al. 1995). They researched the relationship of avian population and its diversity related to forest size and its structure. Friesen et al. (1995) found out that development close to the edge decrease the population of avian, no matter what forest size is. Donovan et al. (1995) did the similar approach to their study. They researched the relationship of the population of Neotropical migrant birds and degree of fragmentation in source habitat. The authors recognize that fragmentation of the source habitat lead to declination of the total population of the species. They perceived under two scenarios: having weak sources and having strong sources. When the fragmented area was weak and which has low productivity to support the population, connectivity to the available natural habitat is important to maintain both population size and its structure. As another circumstance, when the fragmented area was strong and which has large productivity to support the population, little connection to the natural habitat does not affect to the total population to maintain its population size and its structure.Bolger et al. (1997) studied coastal area of the San Diego County, California that covers 260 km2 and includes continuous from chunk of undeveloped shrub habitat area into internally fragmented area and into discrete pattern of habitat area in an urban matrix. They found out that the population of the edge sensitive migrant birds declined between 200 to 500 meters of an edge, whereas the population of the edge/fragmentation enhanced species increased up to 1000 meter from an edge. 5. Suggestions:There are a few considerations that I will point out in managing wilderness area that is habitat area for migrant birds. As Bolger et al. (1997) pointed out, most of the study based on GIS analysis tends to fix the relationship between species abundance and habitat structure. This may underestimate the risk of sensitive species on heterogeneous landscape because there is a possibility that the abundance of the edge sensitive species could differ corresponding with landscape location. Considering ecological features in the forest and recognizing threshold for housing development which could influence forest function is another consideration to manage wilderness area, especially when planning and practicing development on forest edges. Friesen et al. (1995) did survey and found discovered that the abundance of the Neotropical migrant bird communities was richer in 4-ha woodlots without any nearby house than 25-ha urban woodlots .
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