Quantifying market prevalence, abundance, and suitable habitats of bulbuls in Java, Indonesia

Abstract

The prevalence of bulbuls in the Indonesian cage bird trade raises concerns about its impact on their distributions and, consequently, the ecological balance. This study delves into the trade dynamics of bulbuls, examining their market prevalence and its correlation with their abundance in the wild and their suitable habitats. We conducted bird market surveys across Java, supplemented by online trade surveys to ascertain market prevalence. Concurrently, we collected bulbul's presence data from three databases and field surveys from 2018 to 2023. We used a Random Forest algorithm to predict the suitable habitats for bulbuls. The findings revealed that 20 bulbul species, comprising 11 native and 9 non-native to Java, were encountered in 20 bird markets, totalling 35,715 individuals. Sooty-headed (Pycnonotus aurigaster) and yellow-vented (P. goiavier) bulbuls, both Least Concern, dominated the field-RAI (Relative Abundance Index) and trade-RAI. Notably, rare species such as the straw-headed bulbul (P. zeylanicus, Critically Endangered) and extirpated from Java, were present in markets. We found no relationship between the field-RAI and the trade-RAI, suggesting that all species were sought after regardless of their abundance. However, we found that threatened species face over-harvesting based on the ratio between trade-RAI and field-RAI. A significant portion of predicted suitable habitats for resident species fell outside bird-friendly areas. Urgent intervention measures, targeting small-scale agroforestry landowners and key sites for population protection, are imperative to mitigate the potential ecological consequences of the bulbul trade and ensure their continued contribution to tropical ecosystem health.