23-May-2019: Extinct bird reappears
The white-throated rail is the only flightless bird known in the Indian Ocean area. New research has found that it had once gone extinct, but rose from the dead thanks to a rare process called “iterative evolution”. It means the repeated evolution of similar or parallel structures from the same ancestor but at different times.
The study, from the University of Portsmouth and the UK’s Natural History Museum, is published in the Zoological Journal of the Linnean Society. It found that on two occasions, separated by tens of thousands of years, a rail species was able to colonise an island called Aldabra and subsequently became flightless on both occasions. The last surviving colony is still found on the island.
The white-throated rail is a chicken-sized bird, indigenous to Madagascar. Migrating to Aldabra, the rails evolved so that they lost the ability to fly. However, Aldabra disappeared under the sea during an inundation event around 136,000 years ago. The researchers studied fossil evidence from 100,000 years ago when the island was recolonised by flightless rails, and compared with fossils from before the inundation event. They concluded that one species from Madagascar gave rise to two different species of flightless rail on Aldabra in the space of a few thousand years.
3-May-2019: Man-made earthquakes triggered by fracking and dams are not localized
Seismic activity triggered by human actions like construction of large reservoirs or injection of wastewater into the ground for oil and gas production can have far greater implications than previously thought.
While it is well known that injection of fluid into subsurface of the earth (one kilometer deep) can cause events like earthquakes, it was believed till now that such disturbances are limited to an area near the site of injection. The new study has found that subsurface disturbances due to fluid injection can result in earthquakes spread over larger regions, going far beyond the area invaded by the injected fluids. This means, earthquake-triggering stresses can travel far.
In India, the most famous fluid-induced earthquake had occurred in 1967 at Koyna in Maharashtra and was attributed to seismic activity generated due to the impoundment of the Koyna dam there. Earthquakes occurring in tectonically quiet region of Oklahoma have also been linked to oil and gas exploration activity there. It is believed that such regions of man-made earthquake activity surpass the level of seismic activity in hotspots like southern California.
In the new study published in the journal Science, researchers from India and America used data from earlier experiments and a hydro-mechanical model developed by them to explain the full dimensions of fluid-induced earthquakes. The field data came from experiments done in France by the University of Aix-Marseille and the University of Nice Sophia-Antipolis.
Our study shows that fluid-injection has the potential to cause significant, rapidly spreading earthquake activity beyond the fluid diffusion zone.
Oil and gas extraction using fluid injection, as well as wastewater disposal, is known to increase seismicity rate in surrounding regions. Tremblors attributed to these activities have been thought to occur as higher fluid pressures in surrounding rocks trigger instabilities in pre-existing networks of faults. However, injection may also cause aseismic slip—deformation caused along a fault line without any accompanying seismic waves—that may in turn trigger earthquakes.
The field experiments by the French scientists had demonstrated that when fluid injection occurs near existing faults, their primary response could be slow, quiet, aseismic slip rather than violent earthquakes. We used this data to show that aseismic slip could rapidly outpace the region of fluid-diffusion and transmit potentially earthquake-inducing stress perturbations to regions remote from the location of injection.
Understanding the science behind fluid-induced earthquakes could help in unraveling reservoir-induced earthquakes in Koyna. The ‘Deep Drilling at Koyna’ initiative led by Noida-based National Centre for Seismology and CSIR-National Geophysical Research Institute in Hyderabad is studying detailed behaviour of fluid-induced earthquakes in the region. These efforts are expected to yield data about fault behaviour at greater depths in the earth’s crust. Our study is a proof-of-concept of how such data can be used in practice to produce more reliable models of earthquake hazard.
14-May-2019: Herbivore census in Gujarat’s Gir forest
Every summer, the Forest Department of Gujarat conducts a Herbivore Census in Gir forest. This year’s exercise is of particular significance because it is the last Herbivore Census ahead of next year’s Lion Census, which is a once-in-five-years exercise.
The Herbivore Census covers ungulates such as spotted deer, blue bulls (nilgais), sambars, Indian gazelles (chinkaras), four-horned antelopes (choshinga) and wild boars, as well as Indian langurs and peafowl.
Wild ungulates and langurs are the main prey of Asiatic lions, the endangered species whose only wild population in the world is surviving in the 22,000 sq km Greater Gir area. A count provides a sense of the available of the prey base for lions as well as other predators like leopards, hyenas and wolves. A strong prey base can reduce depredation of livestock by lions and can reduce man-animal conflict. In 2013-14, the last Herbivore Census before the previous Lion Census, the total count of all herbivores was 1.32 lakh, higher than the about 1.25 lakh counted in 2012-13.
During summer, foliage is reduced to a minimum in dry and deciduous tropical forests, which affords the best visibility for conducting a census. Also, wild animals concentrate around water points, which in Gir include 450 artificial ones filled by the Forest Department. The forest is divided into 19 routes and forest divisions for the census, with teams transacting routes thrice — morning, afternoon and evening — and depending on direct sighting.