How diminishing
wetlands are harming migratory birds
What exactly are wetlands anyhow?
The U.S. Fish and Wildlife Service defines a wetland as land
that transitions between aquatic and dry where the water table is near the
surface of the land. Shallow water may cover all the land and supports aquatic
plants, hydric soil is predominate and the land is covered seasonally by water
(USDA, 2012).
Why are wetlands in
trouble?
According to the United States Environmental Protection
Agency, approximately 58,500 acres of wetlands were lost each year in the
United States between the years of 1986 and 1997 (EPA, 2012). Most wetland destruction was caused by human activity. Many
wetlands were drained, dredged and made into canal systems to support
agriculture. Logging and mining also played a role in wetland degradation. Declining water quality and loss of wetland habitat can be
caused by several factors. Runoff from farms or golf courses coupled with air
pollution, can add extra minerals and toxins into the already fragile ecosystem
of a wetland, causing decreased water quality.
Encroaching housing
developments, expanded agriculture and the introduction of non-native species
all contribute in part to the problems wetlands are facing throughout the
United States. There are also increasing natural threats to wetland areas from
hurricanes, rising sea levels and erosion. Fortunately, wetland protection
measures have helped slow down the loss of wetlands. Strict governmental
guidelines, public education and huge restoration projects continue to protect remaining wetland areas in the
United States (EPA, 2012).
Migratory Birds and
their relationship to wetlands.
One third of all bird species in North America utilize
wetlands for food, shelter breeding and social interaction. (Kroodsma, 1979).
There are 836 species of birds protected in the United States under the Migratory
Bird Treaty Act. One quarter of those are known to be declining in population
(USFWS, 2002). Several factors affect the relationships of birds and wetlands.
The quality and depth of the water in a wetland, varies food availability and
shelter; as well as promotes changes in behavioral patterns of the migratory
birds (USFWS, 2002).
The relationship between wetlands and migratory birds is
mutual. Wetlands themselves are dependent on the birds for maintaining overall
stable conditions. Wading birds play an important role in the ecological
fitness of wetland ecosystems. They redistribute nutrients and affect the
demographics of fish and invertebrate populations through predation (Frederick,
et al., 2008, cited in Arrieta, 2012, p.1).
Difficulties
migratory birds face from depleting wetlands.
One of the most detrimental consequences of wetland
reduction to breeding migratory birds is population loss. Even though the birds
will move to other habitats, the conditions may be less suitable and
recruitment (birth) rates will start to decline, while mortality rates will
rise. Over the years these populations will no longer be sustainable (Bressler
& Paul, 2012).
Habitat loss forces larger numbers of migratory birds to
inhabit smaller spaces. This adds considerable stress and forces competition
for limited resources. Large numbers of birds promote valuable vegetation loss
and diminish water quality. This leads to a higher risk of disease transmission
among the birds, as well as interspecies transfer (Post, et. al, 1998).
The emergence of infectious diseases is increasing. Wild
birds are widely recognized as natural hosts (reservoirs) of several diseases,
such as bird flu (Avian Influenza). Aquatic environments play a key role in the
transmission of this disease through an indirect fecal-oral route (Zhang, et.
al., 2011). Since these migratory birds travel long distances, they may
possibly shed the virus along their flight routes. The virus can persist in the
environment, posing the risk of exposure to other birds or animals using the
same habitat (Zhang, et. al., 2011).
With shrinking habitat, migratory birds have a greater
chance of coming in contact with domestic farm raised poultry and livestock.
The virus associated with Avian Influenza can be transferred through fecal and
nasal discharge. Insects and rodents can also potentially carry the virus to
domestic flocks. Avian influenza persists for long periods, leaving opportunity
for a high risk of transmission of the virus (Jacob, et al., 2011).
References:
Arrieta, Diane, 2012. Impact of humans on biodiversity.
Class paper. University of Edinburgh. Unpublished.
Bressler, D.W. and Paul, M., Effects on Eutrophication on
Wetland Ecosystems.TetraTech.com Online.
Available at :
http://n-steps.tetratech-ffx.com/PDF&otherFiles/literature_review/Eutrophication%20effects%20on%20wetlands.pdf
[Accessed on 26/09/2012].
CERP (Comprehensive Everglades Restoration Project), 20112.
Online. Available at: http://www.evergladesplan.org/facts_info/faqs_cerp.aspx#1
[Accessed on 25/09/2012].
EPA (Environmental Protection Agency), 2012. Wetlands. Online.
Available at: http://water.epa.gov/type/wetlands/types_index.cfm [Accessed on
24/09/2012].
EPA (Environmental Protection Agency), 2012. Wetlands,
Status and Trends. Online. Available
at:http://water.epa.gov/type/wetlands/vital_status.cfm
Jacob, J.P., Butcher, G.D., Mather, F.B, and R.D. Miles.,
2011. Avian Influenza in Poultry. University of Florida. Online. Available at:
http://edis.ifas.ufl.edu/ps032 [Accessed on 27/09/2012].
Kroodsma, D. E., 1979, Habitat values for nongame wetland
birds, in Greeson, P.E., Clark, J.R., and Clark, J.E. eds., 1979, Wetland
functions and values--The state of our understanding: Minneapolis, Minn.,
American Water Resources Association, p. 320-34
USDA (United States Department of Agriculture), 2012. Hydric
Soils – Introduction. Online. Available at:
http://soils.usda.gov/use/hydric/intro.html [Accessed on 24/09/2012].
USGS (United States Geological Survey), 2012. Wild Birds and Emerging Diseases: Avian
Influenza Transmission Risk and Movements of Wild Birds from Kazakhstan.
Online. Available at: http://www.werc.usgs.gov/Project.aspx?ProjectID=39
USFWS (United States Fish and Wildlife), 2002. Migratory
Bird Mortality Fact Sheet. Online. Available at:
http://www.fws.gov/birds/mortality-fact-sheet.pdf [Accessed on 28/09/2012].
Wetlands : Characteristics and Boundaries 1995, n.d.:
National Academy Press, eBook Collection (EBSCOhost), EBSCOhost, Available
at:
http://www.nap.edu/catalog.php?record_id=4766#toc [Accessed 25/09/2012].
Zhang, Hongbo, Xu,
Bing, Chen, Quanjiao, Chen, Jianjun, Chen, Ze, 2011. Characterization of
an H10N8 influenza virus. Virology Journal V.8:42. Online. Available at:
http://www.virologyj.com/content/8/1/42 [Accessed on 27/09/2012].
Original version of this post was produced for a class at Edinburgh University and is property of the university and the author.
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