Changes in the composition of montane mixed species bird flocks in primary and logged forest in response to climate-driven elevational range shifts

Bhat, Akshiti (2023) Changes in the composition of montane mixed species bird flocks in primary and logged forest in response to climate-driven elevational range shifts. Masters thesis, Indian Institute of Science Education and Research Kolkata.

Text (MS dissertation of Akshiti Bhat (18MS104)) Thesis_18MS104.pdf - Submitted Version Restricted to Repository staff only Download (2MB)

Abstract

One of the most remarkable instances of group behaviour in the animal realm is that of mixed-species bird flocks (MSFs). MSFs provide individuals with decreased predation risk and/or increased foraging efficiency. According to recent research, participation in MSF gives long-term survival benefits in the face of anthropogenic change. Understanding how the species composition changes over time and geography can help identify areas more vulnerable to climate change's effects. In this study, I analysed how the size, structure, and composition of MSF networks changed with time (effect of climate change) and space (effect of logging) between 2015-16 and 2022-23 (8 years). It suggests that logging considerably impacts the composition of MSFs, and climate change may further worsen the impacts of forestry. I conducted this study in the montane wet temperate forest at 2000m asl in the Eastern Himalayas in the Eaglenest Wildlife Sanctuary, West Kameng district, Arunachal Pradesh, India (27.07°N; 92.40°E). I used network analysis to investigate how various species interact in MSFs in primary forests and how these networks changed between the winters of 2015-2016 and 2022-2023 (i.e., over time). I compared species participation and composition of MSFs in primary and logged forests in the Eastern Himalayas over time due to elevational range shifts caused by climate change. Climate change affects species composition in mixed-species flocks, with lower-elevation species increasing in abundance and higher-elevation species declining in abundance. The study compared species participation and composition between the winters of 2015-2016 and 2022- 2023. Climate change was found to influence species composition, with lower-elevation species increasing while higher-elevation species declining in abundance within MSFs. Comparing the two time periods, significant changes were observed in the association networks of understory MSFs. There was a decrease in the number of nodes, edges, edge strength, and density, indicating dispersal and loss of cohesiveness. Modularity increased, suggesting a higher degree of clustering or partitioning, while degree centrality decreased. Furthermore, betweenness centrality increased, signifying certain species' increased importance in facilitating connections between other nodes. The study's findings imply a transitioning primary and logged forest environment, with changes in flock structure and increased resource competition among surviving bird species. The decrease in edge strength in logged forests indicates reduced species interactions due to disturbance or other causes. These alterations in network structure reflect the shifting nature of the forests over time, influenced by climate and elevation shifts, logging activities, and habitat fragmentation. It concludes that a better understanding of MSFs' responses to changes in environmental conditions, including logging, can inform practical conservation approaches to protect the diversity and functioning of forest ecosystems.

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