In a study conducted in several locations in the state, including Pune, the Deccan Plateau, and in and around Alibaug and Chiplun, researchers from the city-based Ela Foundation and the Indian Institute of Science Education and Research (IISER) has found that the Indian Eagle Owl (IEO) Bubo bengalensis plays a positive role in the biological control of crop pests.
The team studied the habitat preference, diet and reproductive behaviour of IEO, and found that its diet is dominated by agricultural pests, which contribute 88% of the total prey biomass. Out of the 13 rodent prey species, which comprise a major part of the diet, seven have been identified as major agricultural pests. Since the owl species is still hunted due to superstitious beliefs, scientific evidence elucidating the importance of the IEO in agricultural pest control can be an important motivation for its conservation.
Satish Pande, ornithologist and founder-president, Ela Foundation, an NGO devoted to nature education and conservation, said, “Despite developments in the infrastructure for production and storage of agricultural produce, it is estimated that rodents damage between 2-15% of the crops annually in the country. Therefore, agricultural pest control is a major concern. In India, we have the concept called IPM – Integrated Pest Management, under which the biological control of pest is included. Not much work has been done on the subject of birds as controllers of pest. Hence, this research is important.”
Pande said chemical control using pesticides and biological control through predators and pathogens have been suggested for pest control. “However, chemical pesticides and control of pests using pathogens often affect the environment and human health. Hence, utilisation of natural predators is an environment-friendly solution. If the importance of wildlife in pest control can be backed up with convincing data, predation by wildlife can be promoted as an environment-friendly pest control method,” Pande added.
This is particularly true for predators like owls, which are often killed as they are considered bad omens, and also for their use in black magic.
During the breeding season between October and March, in 2004-05 and 2005-06, researchers identified 44 occupied nest sites. They selected an area of 1,000 m radius centred on the nests to analyse the landscape features in the nest territories. “We categorised each circular plot into six habitat categories: agriculture, scrub, grassland, water body (perennial or seasonal), hills, and rural habitat, using ‘look down’ visual surveys conducted from high vantage points and estimated the percentage occurrences of each category,” said Pande.
Neelesh Dahanukar, an IISER fellow, added: “At least five visits were made to each of the nest sites each year during the breeding seasons. Owl pellets and prey remains were collected from all nest sites and were separately analyzed for each nest for every breeding season.”
Analysis revealed that IEO’s preference for different habitats was significantly different, with a preference for agriculture dominated habitats than the second most dominant, grassland habitat. “Even though our analysis of the diet suggests that the IEO is a dietary generalist, the abundance and total biomass of different groups of prey in the diet showed that rodents were the most important prey followed by birds and bats. Of all prey items, 73% of relative abundance and 81% of prey biomass was of pests of agricultural significance,” said Dahanukar.
Pande added the study, which was recently published in the Journal of Threatened Taxa, also found that owls have a high productivity in the agriculture habitat, which could be attributed to the increased access to rodents. “As a result, owls are not just the predators of rodents, but are in turn dependent on them to increases their productivity. Therefore, there appears to be a delicate interdependence between owls and rodent populations.”