Estimating density of secretive terrestrial birds (Siamese Fireback) in pristine and degraded forest using camera traps and distance sampling

Abstract

Tropical Asian Galliformes are secretive and difficult to survey. Many of these species are considered “at risk” due to habitat degradation although reliable density estimates are lacking. Using camera trapping and distance sampling data collected on the Siamese Fireback (Lophura diardi) in northeastern Thailand, we compared density estimates for pristine and degraded lowland forest. Density was poorly estimated using distance sampling, likely due to small sample size arising from poor visibility in dense vegetation and bird’s sensitivity to observers. We analysed camera trap data using both count-based and presence/absence-based methods. Those density estimates had narrower confidence intervals than those obtained using distance sampling. Estimated density was higher in dry evergreen forest (5.6 birds km−2), than in old forest plantations (0.2 birds km−2), perhaps because dense forest habitats provide Firebacks with more resources and refuge from predation. Our results suggest that camera trap data can be used for estimating density of cryptic terrestrial bird species inhabiting tropical forest that lack unique identification markings. However, this technique requires that the effective sampling area is known and thus requires knowledge of the animal home range size.