Context: Recently, the Rajasthan government has decided to build temporary shelters for migratory birds near the Sambhar Lake (near Jaipur) before 2020’s winter season.

Issue

• Every year, a large number of birds from the cold northern regions of Central Asia come to Sambhar Lake.
• In 2019, more than 20,000 migratory birds died due to avian botulism in the lake.
• Rajasthan High Court took suo motu cognisance of the mass death and asked the expert committee to carry out an investigation and make recommendations.
• The Court has constituted a seven-member expert committee to study the impact of salt-forming and identify any illegal salt mining in the lake.
• It has suggested the state government seek the centre’s support for more funds for creating an infrastructure for the safety and security of birds.

About Avian Botulism

• Botulinum is a natural toxin produced by bacteria known as Clostridium botulinum.
• It produces the toxin when it starts reproducing.
• The bacteria are commonly found in the soil, river, and sea water.
• There are around eight types of botulinum toxins – A, B, C1, C2, D, E, F, and G.
• All types of toxins attack the neurons, which leads to muscle paralysis.
• It reproduces through spores and these spores remain dormant for years.
• They are resistant to temperature changes and drying.
• Under favorable conditions, the spores are activated.
• Botulinum affects both humans and animals but botulinum C affects birds and A, B and E affects humans.

Case in Sambhar Lake:

• The avian botulism that caused the mass die-off at Sambhar was caused by the climate.
• Due to a good monsoon, the water level reached the lake bed after a gap of 20 years which provided a favorable environment for the bacteria to spread.
• The temperature of the water was about 25 degree Celsius and its pH ranged between 7.4- 9.84, thus providing anaerobic conditions for bacteria to grow.
• The monsoon brought with it a large population of crustaceans (like shrimps, crabs, and prawns), invertebrates (snails) and plankton (like algae) which are capable of hosting the bacteria for a long period of time.
• After the monsoon, when the water levels receded, due to increase in salinity levels these living organisms would have died and the spores could have been activated.
• According to another theory, ‘a bird-to-bird cycle’ has led to the tragedy. In this case, maggots feeding on dead birds can concentrate the toxin. Birds feeding on dead birds can get affected. This was observed in Sambhar too as researchers found only insectivorous and omnivorous birds affected and not herbivores.
• However external factors like water pollution and eutrophication have been rejected.

Other instances of botulism

• Sambhar lake is not the first instance where deaths due to botulism have been recorded. According to reports 7,000 water birds died in Lake Michigan in 2007 and 2008, followed by another 4,000 in 2012. In Hawaii, the toxin killed around 183 Laysan Ducks in 2008.

About Sambhar lake

• Also known as Shakambari Jheel, is India’s largest inland Salt Lake, which is bowl shaped.
• It is not part of the Ganga river basin area and is geographically a separate landlocked river basin.
• It is surrounded on all sides by the Aravalli hills.
• It is a Ramsar site because the wetland is a key wintering area for tens of thousands of flamingos and other birds that migrate from northern Asia.
• The specialized algae and bacteria growing in the lake provide striking water colors and support the lake ecology that, in turn, sustains the migrating waterfowl.
• The other wildlife in the nearby forests includes Nilgai move freely along with deer and foxes.