The coffee plantations of Chikmagalur in Karnataka have a healthy mix of crops and trees, a practice known as agroforestry. These plantations are inhabited by several species of insectivorous bats, which act as a natural pest-control system. A new study investigates the present diversity of such bat species under changing habitat conditions.
Traditional farming practices where crops are grown along with trees and shrubs have been shown to be useful for maintaining biodiversity. This practice, also known as agroforestry, provides sufficient tree-cover to harbour many animal species. One major agroforestry hub in India is the shade-coffee plantations of the Western Ghats, which have coffee crops mixed with trees and are home to diverse species of wildlife.
Particularly of interest to Ongole were insectivorous bat species. Insectivorous bats feed on insects and use echolocation to navigate through their habitats and hunt prey. According to Ongole, these bats are important pest control agents in agricultural landscapes.
“Historically, insectivorous bats in agricultural landscapes have been less studied in Paleotropical regions (Africa, Asia and Oceania) when compared to the Neotropics (Central and South America),” says Ongole, “This study addresses this significant bias.”
Ongole surveyed 30 shade-coffee plantation sites during the dry season (Nov-April) over a period of two years (2015−2017) and collected data on prevalent bat species as well as the landscape features of each site. To do this, the researchers installed acoustic detectors across the study sites that could record ultrasonic signals from free-flying bats. They then compared these calls with existing databases of bat echolocation call patterns to identify the species.
Insectivorous bats are classified on their ability to differentiate between prey and the background landscape. Open-space foragers hunt while in flight and thrive in spaces that do not have dense tree cover. Edge-space foragers hunt airborne insects and are found near the edges of vegetation, buildings or slightly above the ground or water. Clutter-space foragers, on the other hand, hunt by plucking insects from the ground, leaves or branches of shrubs or trees. They require dense tree-cover and shrubs to hunt insects.
The researchers identified nine species of insectivorous bats in these farm-sites. Four were clutter-space foragers (of Rhinolophus sp and Hipposideros sp). The other five were edge-space foragers of the Family Vespertilionidae. The study found no correlations between landscape features (e.g. built-up area, proximity to a forest etc.) and diversity of bat species. But, interestingly, the researchers found that the edge-space foragers, for whom a shade-coffee plantation would usually be considered too dense a landscape for effective hunting, appeared to be more active than clutter-space foragers.
This indicated that these edge-space species adapted well to the cluttered environment by developing clever ways to hunt in a non-native landscape, for e.g. hunting in tracks or clearings in the farm-site. This observation agrees with previous studies on edge-space foragers, which show that these species are more flexible in adapting to different habitats compared to cluttered-space foragers. It also explains why some cluttered-space forager species are threatened more by habitat loss. An example of this is the Beddome’s horseshoe bat (Rhinolphus beddomei), which was detected in very few numbers in this study.