Bird Assemblage and Diversity along Different Habitat Types in a Karst Forest Area in Bulacan, Luzon Island, Philippines

Little is known on the effects of degradation and disturbance on bird assemblage in lowland karst forests in the Philippines. In this study, we determined diversity patterns and distribution of birds along the vertical strata in two karst forest fragments adjacent to and one reforestation area within an active limestone quarry area in Bulacan province, Luzon island. Surveys were conducted using mist nets set in the understory (0–3 m) and sub-canopy (4–10 m) from November 2013 to October 2016. A total of 617 individuals belonging to 63 species and 13 feeding guilds were recorded from a mist-netting effort of 654,264.8 mist-net hours (m2∙h); of these, 32 are Philippine endemics and six are threatened species. We recorded the highest number of species in the reforestation area, most of which are generalist and disturbance-tolerant species. Results from permutational multivariate analysis of variance (PERMANOVA) and non-metric multidimensional scaling (NMDS) indicate differences in bird assemblage between the three habitat types and between the two vertical strata within habitat types. Meanwhile, similarity percentage analyses and Mann-Whitney U tests showed that species and guilds that contributed to the observed dissimilarity in the two strata have higher capture rates in the understory. These observations provide insights into the effect of disturbance and habitat alteration in the vertical movement of birds, as evidenced by the shift of some arboreal species to the understory layer in more disturbed habitats. Understanding the behavior and habitat use of birds will, thus, help in identifying appropriate conservation measures to ensure proper resource partitioning among the different bird assemblages in fragmented habitats.