Indian heronries need conservation monitoring
Most agencies are reluctant to invest in such audits as they require a continuous supply of funds and commitment to science, says Abdul Jamil Urfi*.
doi:10.1038/nindia.2020.12 Published online 23 January 2020The Keoladeo National Park ‒ a UNESCO World Heritage site in India’s Rajasthan state ‒ looked enchanting once upon a time. In its heydays, this picturesque Ramsar site featured in the Hollywood film 'Siddhartha' (based on a Herman Hesse novel of the same name). Today it is a parched version of its former glory.
One of the park’s distinctive features was the presence of extensive heronries — nesting colonies of storks, ibises, spoonbills, herons and cormorants. Spread across many blocks of the 2,873-hectare mosaic of wetland, swamp, forest and scrub, this park also hosted thousands of migratory waterfowl, including the endangered Siberian crane Leucogeranus leucogeranus, during winter.
There were close to 2,500 nests of just one species, the painted stork (Mycteria leucocephala), in the middle of the 20th century1. Half a century later, only about a few hundred nests per year can be counted, and they are restricted to just a few blocks.
The curious case of Delhi's painted stork colony
Just a couple of hundred kilometres away, in India's capital Delhi, some painted storks began building a colony inside the National Zoological Park around 1960. The colony thrived on islands of mesquite trees in the zoo's open ponds. This nesting colony, strangely sandwiched between the historical monuments of Old Fort and Humayun’s Tomb, came up quite accidentally.
Sixty years later, Delhi has seen unprecedented growth, its feeder river Yamuna murky with pollution and the river's floodplains encroached with human settlements. Surprisingly, these adverse conditions have done nothing to the zoo colony, to which the painted storks continue to add almost 200 nests every year.
These two sites present a picture in contrast. While in a natural site such as the Keoladeo bird sanctuary, the colonies of painted stork have worn out; their populations have remained stable in urban Delhi despite environmental degradation and loss of foraging habitats near the zoo premises.
What could possibly be the reason behind these contrasting trends? In the Keoladeo sanctuary, alterations in water regulation policies by the Rajasthan state government have decreased the quantity and quality of water supply needed in the park for rejuvenation of the aquatic food webs. In Delhi zoo, however, the security of the park premises explains why painted stork and other species of heronry birds continue to prefer it as a nesting site despite loss of foraging habitats outside the premises.
Lack of long-term data
The more significant issue here is of lack of long-term records of populations or nesting parameters to be able to understand the effects of environmental change on biodiversity. In both cases cited above1, I had to cull nesting records from old books, sporadic reports in journals and even student dissertations.
In other words, there is a strong need for conservation monitoring programmes that can be sustained over long periods, with mechanisms in place to ensure regular data gathering by trained personnel.
The monitoring of birds with a long-term, conservation perspective, often supported by citizen science, has paid rich dividends in basic and applied ecological research. For instance, among the initial studies to demonstrate the effect of global climate change on bird nesting patterns in Europe, the investigators relied upon long-term population records maintained by various agencies2, 3.
The heronry census in the United Kingdom, which gathered nesting records of the grey heron (Ardea cinerea) for over 100 years, is often used as a textbook example of how abiotic factors (winter temperatures in this case) regulate bird population trends over the long term.
Despite the known benefits of long-term population monitoring, most agencies are reluctant to invest given that it requires a continuous supply of funds, commitment to science, strict adherence to a protocol and coordination activities. India has had a mixed record of monitoring biodiversity, with some of its wildlife monitoring schemes also coming under a cloud. For instance, the tiger census has been challenged over methodological issues since its inception in the 1970s.
With respect to birds, a significant start was made with the Asian Waterfowl Census (AWC) in 1982 by international agencies such as the Waterfowl Trust and Wetlands International (and later taken over by Indian NGOs such as the Bombay Natural History Society). The AWC4 has yielded many positive dividends over the years. But it has also faced challenges that come with crowd-sourced biodiversity data-gathering programmes, such as misidentification of bird species by poorly trained amateur volunteers, deviations from protocol and data gathering concentrated around urban and semi-urban regions.
Showcasing the nesting phase ‒ a significant chapter in the life cycle of birds ‒ heronries offer a great educational opportunity. Therefore, a monitoring programme involving students and researchers can be beneficial for both.
Focus on nests
However, unlike bird-counting programmes, heronry programmes place emphasis on nests. Fortunately, nests are stationary structures that can't fly off, unlike their makers. The focus in nest-monitoring programmes is on the contents of the nest — eggs and nestlings — besides information on parent birds in attendance. By repeated visits to the same nest, one obtains estimates of nest success ‒ an important parameter in conservation biology that helps accurately understand how birds respond to change in their habitat. Now, with specialised software, some agencies have started programmes to monitor nest success with volunteer efforts. The Nest watch programme of the Cornell Lab of Ornithology is a case in point.
Having a monitoring programme for heronry birds, which include species of storks, ibises, spoonbills, herons and cormorants, is the need of the hour in India because of its relevance for conservation5. Several species in this group, listed as threatened taxa, are also colonial nesters.
Many of the fish eating heronry birds are apex predators in the aquatic food chains. Therefore, any fluctuation in their principal food source fish (for instance, due to climate change) is likely to be picked up in monitoring exercises, alongside changes in their foraging habitat due to urbanisation6 and pollution (especially pesticides).
Heronries can be monitored relatively easily. Many of them are located in approachable urban areas. Besides the painted stork colony at the Delhi zoo, many large nesting colonies or heronries have become permanent fixtures in other Indian cities such as Mysuru and Bhavnagar.
(*The author is an Associate Professor at the Department of Environmental Studies, University of Delhi.)
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3. Both, C. et al. Climate change and population declines in a long-distance migratory bird. Nature 441, 81-83 (2006)
4. Urfi A. J. et al. Counting birds in India: methodologies and trends. Curr. Sci. 89, 1997–2003 (2005)
5. Rahmani, A. R. Threatened birds of India: Their conservation requirements. BNHS & OUP (2012)
6. Urfi, A. J. Using heronry birds to monitor urbanization impacts: A case study of Painted Stork Mycteria leucocephala nesting in the Delhi Zoo, India. Ambio 39, 190-193 (2010)