Garima Prasher
31 Oct 2022
'Nests removed’ from Sankey, where 38 cormorants, 23 nests were recorded
The presence of humans in and around lakes of Bengaluru is altering bird behaviour, research has found.
A study conducted by a researcher at Jain University has discovered that proximity to humans is impacting the nest-building behaviour of the Great Cormorant, a bird seen at lakes across Bengaluru. The study wasrecently published in the Indian BIRDS journal. The study examined in detail the behaviour patterns of the Great Cormorants that were nesting on the eucalyptus trees at Sankey and Kaikondrahalli lakes. The researcher found that cormorants at Sankey Lake were more vigilant at the nest sites and constructed nests at a higher level compared to Kaikondrahalli.
The nest height on the trees varied from 8.4 m to 12.6 m from the ground level at Sankey Lake, whereas it was recorded from 4.2 to 12.2 m above the ground level at Kaikondrahalli.
“Anthropogenic pressures could be a major factor affecting nest-building behaviour in these birds. All through the study period, the cormorants at Sankey, with a higher level of human movements at the waterbody, weresensitive to human disturbance in comparison to Kaikondrahalli Lake. Thus, the nests were constructed much higher at Sankey than at Kaikondrahalli where the trees were away from human movement and were partlysubmerged in the lake,” said Dr KS Chetan Nag , author of the study and associate professor at Jain University.
Interestingly, the distance between the nesting trees and the walking path was 0-1 m at Sankey Lake and around 40 m at Kaikondrahalli. Moreover, human density at Sankey Lake varied from 530–1,127 people in themorning, and 584–2,004 people in the evening. At Kaikondrahalli, there were 320–440 people in the mornings and 427–674 people in the evening.
“These birds are generally known to leave the nest anytime between 6:00 am and 9:00 am to forage. We spotted 23 nests with 38 birds at Sankey Lake and observed that not even a single bird left the nest while therewere humans in the area.
They were very vigilant and took off to the lake for foraging once the human density at the walking path decreased around 8:00 am. That is when the walkers leave the lake after their morning walks,” added Dr Nag.
Bursting the myth:
Cormorants preferred eucalyptus to native tree species for nesting. The birds selected seven live eucalyptus trees at Sankey Lake, close to the walking paths, for nesting and breeding. At Kaikondrahalli Lake, 56 birdswith 12 nests occupied 13 dead eucalyptus trees partially submerged in the water.
Eucalyptus trees were the cormorants’ first choice at both sites despite the presence of native trees.
Cormorants took off for foraging… once human density decreased around 8:00 am… when people leftthe lake after morning walks…
— Dr KS Chetan Nag, author of study
“This might be due to the closeness of these trees to the water source. Also, nesting in eucalyptus, and other exotic trees, have been found to have greater breeding success owing to better stability and protectionoffered by those trees compared to native species. Birds are also known to nest in trees that were used by their predecessors for breeding,” explained Dr Nag.
Birds removed from lake:
While the study had recorded 38 cormorants with 23 nests at Sankey Lake, the researcher alleged that all the nests have been removed now by the Sankey Lake walkers’ association.
“I visited the lake a few months ago and was shocked to see that despite my repeated requests, all the nests had been removed. The birds were evicted from their habitat as ‘they were defecating on the walking path’,which reportedly was ‘inconvenient to the walkers at the lake’. It is high time we changed our attitudes towards other species and nature,” lamented Dr Nag.