Long-term changes in avian relative abundances in relation to human disturbance in a tropical dry forest in central Myanmar

Tropical dry forests, including dry dipterocarp forests of Asia, are in jeopardy from increasing human pressures, especially agricultural encroachment, hunting, and probably climate change. Quantifying the impacts of these pressures and implementing effective management solutions have been hampered by a scarcity of regional long-term wildlife monitoring data. Our study examined long-term (22-year, 1999–2020) changes in the relative abundances of six avian guilds at a small-scale (30 survey points) in Chatthin Wildlife Sanctuary in Myanmar’s Central Dry Zone. We focused on common feeding guilds that have significant effects on ecosystem processes, including seed dispersal (frugivores), insect abundance regulation (bark-gleaning insectivores [woodpeckers], foliage-gleaning insectivores, sallying insectivores, and terrestrial insectivores), and seed predation (granivores). We also used data from five focal species within these guilds to further assess long-term trends. Trends in relative abundances were analysed in relation to time (survey year) and forest disturbance. Although the forest within a 300-m radius of the survey points appeared to be only moderately disturbed, relative abundances of frugivores, granivores, and terrestrial insectivores declined over the study period. Woodpeckers declined in response to specific forest disturbance incidents, but did not show long-term declines. Foliage-gleaning and sallying insectivore abundances did not change significantly. Among individual focal species, blossom-headed parakeet (Psittacula roseata) and white-browed fantail (Rhipidura aureola) abundances declined. The parakeet and fantail declines are particularly salient because these two species are typically associated with dry forest, although the parakeet was probably highly impacted by poaching. In contrast, relative abundances of the more generalist common woodshrike (Tephrodornis pondicerianus) increased over time, golden-fronted leafbird (Chloropsis aurifrons) likely also increased, while rufous treepie (Denmdrocitta vagabunda) did not show a clear trend. Although our monitoring data on human disturbance was limited, most declines were probably a consequence of increased human use inside the sanctuary rather than climate change, indicating significant cumulative effects of extensive local human use of the forest during the 22-year period.