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).
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].
Image credit: Seagulls in flight: online available at: http://www.google.com/imgres?hl=en&client=firefox-a&hs=EnZ&sa=X&rls=org.mozilla:en-US:official&biw=1280&bih=895&tbm=isch&prmd=imvns&tbnid=vCSaWLAxdubhqM:&imgrefurl=http://journalweek.com/interesting-facts-about-birds/&docid=P1-vMglTqqwykM&imgurl=http://journalweek.com/wp-content/uploads/2012/07/migratorybirds-uttarpradesh.jpg&w=640&h=429&ei=OK1gUM-QF4qm8ASEpYA4&zoom=1&iact=hc&vpx=183&vpy=198&dur=3320&hovh=184&hovw=274&tx=133&ty=128&sig=103675402944677925378&page=1&tbnh=149&tbnw=199&start=0&ndsp=20&ved=1t:429,r:0,s:0,i:87
Original version of this post was produced for a class at Edinburgh University and is property of the university and the author.