- A research study focusing on the endemic brown-capped babbler (Pellorneum fuscocapillus) and Tickell’s blue flycatcher (Cyornis tickelliae) shows that forest specialist birds fail to return to disturbed lands, and even forest generalists tend to avoid these areas, causing delays in their return.
- Researchers employed a method called “experimental translocation” to understand how species interact with new environments by releasing the birds at various distances in different habitats, monitoring whether the birds returned to their original locations.
- A global review by the same researchers identifies 32 instances in which the experimental translocation method was used to study birds worldwide. The Sri Lankan experiment is the first of its kind in South Asia.
- The research highlights that even highly mobile creatures like birds are affected by forest fragmentation, underscoring that the impact can be even worse for less mobile creatures.
COLOMBO — Forest fragmentation is considered one of the main threats to biodiversity. Many believe this primarily affects small creatures like amphibians and small mammals, while mobile creatures such as birds are less impacted due to their ability to fly.
However, new research coming out of Sri Lanka shows how forest fragmentation can restrict even the movement of birds, especially forest specialists that inhabit the understory of the forest, leaving serious impacts on the feathered kind.
To study this phenomenon, Sri Lankan scientist Salindra Kasun Dayananda of Tsinghua Shenzhen International Graduate School Institute of Environment and Ecology selected two species: the brown-capped babbler and Tickell’s blue flycatcher. The brown-capped babbler (Pellorneum fuscocapillus), an endemic bird that inhabits the understory of forests, is called a forest specialist because it heavily relies on forest habitats for survival. In contrast, the Tickell’s blue flycatcher (Cyornis tickelliae) is considered a forest generalist, capable of thriving in a variety of habitats, including disturbed or fragmented ecosystems.
The research team used a technique called “experimental translocations,” in which they caught birds from forest habitats, tagged them with radio transmitters and released them in nearby rubber or tea plantations at a distance of half a kilometer (0.3 miles). As a control, other birds of the same species were released within the forest patch at the same distance to monitor their homing behavior in comparison with the rubber plantations. The team then tracked the birds using radio transmitter signals to monitor their movements.

“We captured 19 birds: nine brown-capped babblers and 10 Tickell’s blue flycatchers and received results that three of the brown-capped babblers released on rubber plantations couldn’t find their way back to the original forest patch. However, all the brown-capped babblers that were released within the same distance inside the forest patch returned to their original location,” Dayananda told Mongabay.
Using experimental translocation method
In contrast, all the Tickell’s blue flycatchers released in both forested and fragmented habitats returned home, but those released in the rubber plantations took a longer time to reach the original destination. Significantly, the flycatchers mostly used the edges of the plantations, avoiding crossing the rubber plantation to reach their home, Dayananda added.
“This finding indicates that for forest specialists, the barriers created by fragmentation are too much even though they can fly,” Dayananda said. “These birds have typically adapted to the unique conditions found within forest environments and may depend on specific types of trees, microclimates, or forest structures,” he added.
The research is part of Dayananda’s Ph.D. thesis, which faced delays due to COVID-19 lockdowns and a lengthy approval process for using electronic transmitters. “We initially wanted to release the birds 1 km [0.6 mi] away but received permission for only half that distance. Since the birds were out of their home range, that was, however, enough for our research,” Dayananda told Mongabay.

As the research team used radio transmitters, they had to physically follow the birds capturing signals aiming at least two antennae to find the birds’ locations. It was tedious than more modern GPS tags used at present, however GPS tags are bigger, so not suitable for small birds, Dayananda said.
Experimental translocations are ideal to study species’ adaptability and survival in different environments, as it is hard to know how some species react to a kind of land use like rubber plantations, since they may not be living in it, says Eben Goodale of Xi’an Jiaotong-Liverpool University’s Department of Health and Environmental Science. “Through this technique, we move birds across different kinds of land uses and see how they react,” says Goodale, Dayananda’s supervisor.
Tedious research process
A global review by a team consisting of Dayananda and Goodale found 28 instances of experimental translocation methods being used for birds elsewhere. The researchers found a total of 25 studies conducted in the Western Hemisphere, and pasturelands were the dominant land use in 17 locations, Goodale said. The technique has been mostly used with males of small, forest-preferring passerine species, Goodale noted.
However, the recent research in Sri Lanka is the first time the experimental translocation method was used to study birds in South Asia, Goodale told Mongabay.

Birds are naturally highly mobile creatures because of their flight ability. If the birds are also affected by fragmentation, as this study reveals, what about the less mobile creatures such as amphibians, land snails and so on, questioned Sri Lankan ornithologist Sarath Kotagama. Fragmented habitats often cannot support the same diversity of life as contiguous ones. Species with large home ranges, specialized habitat requirements or low population males of densities are particularly vulnerable to extinction, Kotagama said.
Unfortunately, the highest level of fragmentation is reported in highly diverse wet zones where most of Sri Lanka’s forest-dependent species are found.
According to Kotagama, addressing these challenges requires a comprehensive approach that combines conservation, sustainable development and community engagement to preserve and restore the integrity of such forest ecosystems.
Establishing corridors and linkages between fragmented habitats can reduce the impacts of the fragmentation to some extent, he suggested. The research also indicated that even Tickell’s blue flycatchers prefer using the edge of the rubber plantations and avoid having to cross them in order to reach their home range.
Dayananda has specific interests in how urbanization and fragmentation impacts wild species. Further research by Dayananda and team conducted in China looked at the effects of forest fragmentation on nocturnal Asian birds.
Citations:
Seidler, R. (2017). Patterns of biodiversity change in Anthropogenically altered forests ☆. Reference Module in Life Sciences. doi:10.1016/b978-0-12-809633-8.02186-5
Dayananda, S. K., Athukorala, H. F., Peabotuwage, I., Kumara, C., Ranasinghe, T., Samarasinghe, D., … Goodale, E. (2024). Rubber plantations are impermeable to an avian understory specialist in Sri Lanka. Movement Ecology, 12(1). doi:10.1186/s40462-024-00484-8
Dayananda, S. K., Mammides, C., Liang, D., Kotagama, S. W., & Goodale, E. (2021). A review of avian experimental translocations that measure movement through human-modified landscapes. Global Ecology and Conservation, 31, e01876. doi:10.1016/j.gecco.2021.e01876
Dayananda, S. K., Goodale, E., Lee, M., & Liu, J. (2016). Effects of forest fragmentation on nocturnal Asian birds: A case study from Xishuangbanna, China. Zoological Research. Retrieved from https://www.researchgate.net/publication/303753892_Effects_of_forest_fragmentation_on_nocturnal_Asian_birds_A_case_study_from_Xishuangbanna_China
Banner image of a transmitter-fitted Tickell’s blue flycatcher (Cyornis tickelliae), a small passerine bird, also considered a forest generalist with the ability to thrive in a wide range of environmental conditions. Image courtesy of Kasun Dayananda.