Four bat species missing from Delhi amid rapid urbanisation

Bats perform three vital roles in an ecosystem — pest control, pollination, and the dispersal of seeds —and naturalists have recorded the sightings of 14 species of the mammals in Delhi. However, ongoing research by two experts says that over the past decade, at least four species have gone missing from the Capital and have likely become locally extinct.

The experts — Guru Gobind Singh Indraprastha University (GGSIPU) assistant professor Sumit Dookia and his PhD student Rajlakshmi Mishra — have blamed the disappearance of the bat species to a loss of habitat due to urbanisation, a decline in green cover, and most importantly, the improper renovation of monuments which housed these animals.

While Dookia has been analysing bat hotspots and their habitat in the Capital since 2012, Mishra began conducting her research from 2015, and they have found that four species — the Indian false vampire bat (Megaderma lyra), the black bearded tomb bat (Taphozous melanopogon), the Egyptian free tailed bat (Tadarida aegyptiaca), and the Indian pipistrelle (Pipistrellus coromandra) — are no longer seen in Delhi.

Dookia said all four species that have gone missing were earlier spotted at monuments across the city.

“Broadly, we have observed a decline in the number of the specialist bat species, whereas generalist bat species are still thriving. The diversity in species, particularly specialist species over generalist species is one of the key indicators of a healthy ecosystem and at present, it appears that none of these four species exist in Delhi anymore. This is largely linked to renovation practices that are not bat friendly, coupled with declining green areas,” said Dookia.

Generalist bat species can feed on multiple food sources and are able to thrive in a wide variety of habitats and environmental conditions, while specialist bat species survive only in a narrow range of environmental conditions and have a limited diet.

Giving an example of a loss of habitat leading to the disappearance of a bat species, Dookia said the Indian false vampire bat used to be found only at Humayun’s Tomb, as it prefers a jagged rock surface to roost, but after the renovation programme at the monument, can no longer be found in the city.

Another recent monument undergoing restoration is the Malcha Mahal — a 14th century Tughlaq era hunting lodge, located within the Central Ridge forest. The monument, which too has bats roosting inside, is being renovated by Delhi’s department of archaeology, which will see grilles and lighting installed in the complex. Already, 38 trees growing within the monument structure have been felled. The Delhi government has also launched ‘haunted walks’ at the monument, which are held every Saturday and Sunday from 5.30pm to 7pm. Experts feel if correct practices for renovation are not followed, the bats in this case are also likely to abandon the monument.

Manu Bhatnagar, principal director of the Natural Heritage Division at INTACH said Delhi’s numerous monuments and heritage sites have their own unique flora and fauna. However, conservation practices so far had failed to incorporate them in conservation plans.

“If we talk about renovation or protecting these heritage sites, it is important to protect the microhabitats that form there, both in terms of the flora and fauna. A good example of that is Tughlaqabad fort, which has a number of wild plants and diverse fauna, the largest of which are bats. When we talk about renovating monuments, we need to look at co-existing, particularly since bats are nocturnal creatures and will not disturb visitors during the day. Removal of bat droppings is also not a major problem,” said Bhatnagar, stating for rare species, certain sections of monuments can also be kept separate.

There is another reason for the decline in bat numbers — a drop in green cover. Dookia said a fifth bat species may soon disappear from Delhi — the Blyth’s horseshoe bat (Rhinolophus lepidus), which has only one habitat in the Capital: the Aravalli Biodiversity Park in Vasant Vihar. “This is another sensitive species, found away from human habitation and requires a moist and well-wooded area. If there is any disturbance to this current habitat, they too may be under threat,” he said.

Delhi still has several prominent bat hotspots, spread across south, central and southeast Delhi — all fairly green areas. “One of Delhi’s biggest roosting sites for bats is at Janpath, where the Indian flying fox can be seen in large numbers. We have seen good bat diversity in the southern ridge too,” Dookia said.

On the flipside, highly concretised areas in northeast, west, southwest and south Delhi — all devoid of significant tree cover — have little to no bat diversity.

A third reason for a drop in bat numbers is light pollution. According to Dookia, a single insectivore bat is capable of consuming up to 1,000 mosquitoes in a single night. This type of bat, he said, can be broadly divided into two groups: a wide wing span and a short body, or a short wing span with a large body.

Dookia said it is this second group that has been unable to adapt to the large congregations of insects drawn to fixed light sources. “Due to light pollution and high-mast lights, we have created a fixed food source for the Vespertilionidae family bats, which do not have a very specific roosting habitat choice. They are found in almost all residential areas of Delhi. The other category meanwhile has not been able to adapt to such artificial feeding spots that are created by lights.”

Faiyaz Khudsar, scientist in-charge of the Delhi Development Authority’s biodiversity parks programme, said there is a deeper problem that Delhi’s bats face. “A number of fruit bats require large trees to roost and a lot of these older, very large trees in Delhi are gradually vanishing. It could be that they fall during a storm, or are simply not being planted at the same rate as they were earlier. Bats pollinate a number of fruit trees, which includes the chikoo and wild bananas. Frugivore bats are also needed as their droppings allow trees to emerge,” he said, adding that a decline in any bat variety can be damaging to the ecosystem.

“If bats vanish from an area, the insect count there could also spike, as they naturally control pests.”