The Last Migration

Vijaylakshmi Suman

Cities are considered to be concentrated centres of production, consumption, and waste disposal that drive land change. They have also been spaces of several global environmental problems. Most of the cities have historically been established along rivers and deltas in order to have easy access to water. These waterbodies have been modified and used for domestic as well as industrial processes, and in many cases have led to their degradation. Severe discharge of pollutants from industries and sewage contamination of the water channels are known to change the chemical environment of water bodies, coupled with problems such as low biotic diversity, high nutrient concentration and reduced nutrient retention efficiency (Grimm et al., 2008).

Urban water bodies that exist in the form of lakes and rivers are not only used by people who reside in cities, but also act as a resource and provide habitat for a lot of fauna and water birds. Despite being recipients of pollutants from wastewater treatment plants, they continue to provide habitat to a lot of local and migratory waterbirds. However, the use of these polluted water bodies by birds entails a lot of risks and may prove to be fatal.

Image Source: The Indian Express, 22.1.2019

A recent incident at Sambhar Lake (80 km Southwest of Jaipur City) in Rajasthan saw the death of thousands of migratory birds. Sambhar Lake is India’s largest saltwater lake (230 sq. km), which is spread across three cities – Jaipur, Nagpur and a portion of Ajmer. It is also one of the designated Ramsar Sites as every year, thousands of migratory birds fly to the lake. Around 83 species of water birds have been recorded at the lake so far. From reports, around 25-30 species of birds were found dead, including species such as Northern Shoveller (Anas clypeata), Brahminy Duck (Tadorna ferruginea), Kentish Plover (Charadrius alexandrines), and Tufted Duck (Aythya fuligula). According to investigations and evidence collected at the lake, ‘avian botulism’ – a serious neuro-muscular illness caused by a toxin produced by the bacterium Clostridium botulinum – has been suspected to cause the deaths.1

Botulism among waterbirds is commonly known to be a serious and destructive epizootic disease caused due to ingestion of the toxin produced by Clostridium botulinum type C. Most birds may have contracted the infection from the shores of lakes and ponds where oxygen has been depleted by layers of algae and rotten vegetation. Waterbirds are often attracted to such water bodies where they ingest fatal quantities of the toxin that has formed during growth and metabolism of the toxic anaerobe (Crisley et. al., 1968).  

Image source: The Indian Express 12.11.2019

While cities are centres of massive amounts of production and waste disposal, they are also hosts to several global environmental problems. As urban land use and its footprint expand worldwide, the need to maintain diversity and function of biological communities becomes an important course of action. Cities could be considered as real-world laboratories, where ecologists who understand fundamental patterns and processes, can work with city planners, engineers, and architects to implement policies that maximize and sustain biodiversity and ecosystem function. It is likely that the fairly nascent urban ecology discourse will play an important role in finding solutions and direct us to a more sustainable urban future.

References:

  • Grimm, N. B., Faeth, S. H., Golubiewski, N. E., Redman, C. L., Wu, J., Bai, X., & Briggs, J. M. (2008). Global change and the ecology of cities. science319(5864), 756-760.
  • Crisley, F. D., Dowell, V. R., & Angelotti, R. (1968). Avian botulism in a mixed population of resident ducks in an urban river setting. Bulletin of the Wildlife Disease Association4(3), 70-77.

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