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Breeding of migratory bird River Tern in Bhigwan sanctuary under threat due to increasing human interference: Study

Located about 100 km from Pune city along the Pune-Solapur Highway, this reservoir sanctuary, adjacent to the Ujjani reservoir, offers a perfect summer habitat for these birds for breeding and nesting purposes.

Written by Anjali Marar | Pune |
January 11, 2021 10:49:57 pm
Pune Bhigwan Reservoir bird sanctuary, Pune River Tern, Migratory Birds, Migratory Birds breeding, River Tern Breeding season, Indian ExpressA majority of eggs are lost as they are crushed by vehicles and trucks ferrying sand from the breeding sites. (Express photo)

Growing human activities, unchecked cultivation, cattle grazing and mindless tourism activities have together increased the stress on the breeding and nesting of River Tern, a local migratory bird that visits Bhigwan Reservoir sanctuary annually during the summer months.

Located about 100 km from Pune city along the Pune-Solapur Highway, this reservoir sanctuary, adjacent to the Ujjani reservoir, offers a perfect summer habitat for these birds for breeding and nesting purposes.

A four-year-long joint study, undertaken by zoologists Shivaji Chavan of Swami Ramanand Teerth Marathwada University and Arvind Kumbhar from Shankarrao Mohite Mahavidyalaya, Akluj, found that a majority of the River Tern eggs (47 per cent) were destroyed after coming under trucks and similar vehicles ferrying sand from the site.

Another 26 per cent and 21 per cent eggs were lost due to dog predation and cattle trampling, respectively, the recent study highlighted.

“The sand dredging activities are happening on the breeding site, where River Tern commonly breed. The sight of crushed eggs on these breeding spots is very common,” Chavan, lead author from the Marathwada university, told The Indian Express.

Along with Bhigwan in Maharashtra, the River Tern are commonly spotted in Chilika lake in Odisha and in some areas of Tamil Nadu. Bhigwan area is an important transit location for numerous migratory birds including egrets, raptors, several species of cranes and flamingos, storks and others, which set out to travel between Mongolia and its neighbourhood all the way to Indonesia, Malaysia and even upto Australia, in the southern hemisphere.

But most local tourists throng Bhigwan to catch a glimpse of flamingos, leading to a spike in tourism in the locality in recent years.

Now under the ‘Near Threatened’ category, River Tern choose inland areas, preferably near water bodies, for their breeding, mainly during April and May. Hot temperatures, ranging between 38 to 40 degrees Celsius, are considered most ideal for incubation and breeding.

With summer at its peak, water — both in the reservoir and nearby water bodies — hit low levels. “As such, small islands or plateaus develop, which are preferred for breeding,” explained Chavan.

This researcher-duo visited 50 villages and scouted 14 nesting grounds in the locality with an aim to understand the numerous criteria for the River Tern’s site selection for laying its offsprings, in addition to documenting the clutch and egg population in each nest. The researchers managed to spot 870 nesting sites which together had 3,206 eggs, an average of four eggs present in every nest.

River Tern, experts say, thrives on fishes and mollusks in the reservoir. The maximum number of nests, about 322, were spotted at Kedgaon village and 257 nests at Shah village, the study noted.

Other identified causes affecting the breeding include trampling by grazing cattle, motorbike racing, predation by stray dogs and other domesticated animals.

“With most heat-exposed sites in Bhigwan seeing growing human interference, it has turned them into unprotected sites for breeding for River Tern. Joint efforts are needed to conserve such sites, which play a crucial role for migratory birds,” said Chavan.

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