Occupancy and co-occurrence patterns of bulbuls (family: Pycnonotidae) across various environmental gradients in Eastern Ghats, Tamil Nadu, India

Land use and land cover change are the direct causes of the loss of biodiversity, causing species to be threatened in the form of habitat loss and increased chance of extinction from competition between closely related species for limited resources. We used multispecies occupancy modeling to determine the influence of environmental and habitat features on Bulbuls occupancy and interactions between closely related Bulbul species and their occupancy in the presence or absence of other species. During the study, five species of bulbuls were recorded; four belong to the Pycnonotus genus, and the single species belongs to the genus Hypsipetes. Due to the low detection of Square-tailed Bulbul Hypsipetes ganeesa and Yellow-throated Bulbul Pycnonotus xantholaemus, they were not selected for occupancy modeling. Marginal occupancy was estimated for the following three species: Red-vented Bulbul Pycnonotus cafer (Ψ = 0.7229 ± 0.06194 CI: 0.5805–0.8144), Red-whiskered Bulbul Pycnonotus jocosus (Ψ = 0.8023 ± 0.05884 95% CI: 0.6669–0.8844), and White-browed Bulbul Pycnonotus luteolus (Ψ = 0.6602 ± 0.04742 CI: 0.567–0.7458). Conditional occupancy was estimated in the presence or absence of closely related species, and there is no negative interaction between closely related species. We identified environmental variables that affect species presence and absence in the Eastern Ghats. NDVI, canopy cover, agricultural land and plantations are the variables that significantly affect Red-vented Bulbul occupancy probability. The presence of Red-whiskered Bulbul was significantly influenced by dense forest and plantations. Elevation, NDVI, tree height, agricultural land, moderate forest, shrub and plantation are the environmental variables that affect the species occupancy of White-browed Bulbul.